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Annual Review of Plant Biology - Volume 70, 2019
Volume 70, 2019
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From Bacteriophage to Plant Genetics
Vol. 70 (2019), pp. 1–22More LessWhen first asked to write a review of my life as a scientist, I doubted anyone would be interested in reading it. In addition, I did not really want to compose my own memorial. However, after discussing the idea with other scientists who have written autobiographies, I realized that it might be fun to dig into my past and to reflect on what has been important for me, my life, my family, my friends and colleagues, and my career. My life and research has taken me from bacteriophage to Agrobacterium tumefaciens–mediated DNA transfer to plants to the plant genome and its environmentally induced changes. I went from being a naïve, young student to a postdoc and married mother of two to the leader of an ever-changing group of fantastic coworkers—a journey made rich by many interesting scientific milestones, fascinating exploration of all corners of the world, and marvelous friendships.
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Assembly of the Complexes of the Oxidative Phosphorylation System in Land Plant Mitochondria
Vol. 70 (2019), pp. 23–50More LessPlant mitochondria play a major role during respiration by producing the ATP required for metabolism and growth. ATP is produced during oxidative phosphorylation (OXPHOS), a metabolic pathway coupling electron transfer with ADP phosphorylation via the formation and release of a proton gradient across the inner mitochondrial membrane. The OXPHOS system is composed of large, multiprotein complexes coordinating metal-containing cofactors for the transfer of electrons. In this review, we summarize the current state of knowledge about assembly of the OXPHOS complexes in land plants. We present the different steps involved in the formation of functional complexes and the regulatory mechanisms controlling the assembly pathways. Because several assembly steps have been found to be ancestral in plants—compared with those described in fungal and animal models—we discuss the evolutionary dynamics that lead to the conservation of ancestral pathways in land plant mitochondria.
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Chloroplast Lipids and Their Biosynthesis
Georg Hölzl, and Peter DörmannVol. 70 (2019), pp. 51–81More LessChloroplasts contain high amounts of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) and low levels of the anionic lipids sulfoquinovosyldiacylglycerol (SQDG), phosphatidylglycerol (PG), and glucuronosyldiacylglycerol (GlcADG). The mostly extraplastidial lipid phosphatidylcholine is found only in the outer envelope. Chloroplasts are the major site for fatty acid synthesis. In Arabidopsis, a certain proportion of glycerolipids is entirely synthesized in the chloroplast (prokaryotic lipids). Fatty acids are also exported to the endoplasmic reticulum and incorporated into lipids that are redistributed to the chloroplast (eukaryotic lipids). MGDG, DGDG, SQDG, and PG establish the thylakoid membranes and are integral constituents of the photosynthetic complexes. Phosphate deprivation induces phospholipid degradation accompanied by the increase in DGDG, SQDG, and GlcADG. During freezing and drought stress, envelope membranes are stabilized by the conversion of MGDG into oligogalactolipids. Senescence and chlorotic stress lead to lipid and chlorophyll degradation and the deposition of acyl and phytyl moieties as fatty acid phytyl esters.
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Conditional Protein Function via N-Degron Pathway–Mediated Proteostasis in Stress Physiology
Vol. 70 (2019), pp. 83–117More LessThe N-degron pathway, formerly the N-end rule pathway, regulates functions of regulatory proteins. It impacts protein half-life and therefore directs the actual presence of target proteins in the cell. The current concept holds that the N-degron pathway depends on the identity of the amino (N)-terminal amino acid and many other factors, such as the follow-up sequence at the N terminus, conformation, flexibility, and protein localization. It is evolutionarily conserved throughout the kingdoms. One possible entry point for substrates of the N-degron pathway is oxidation of N-terminal Cys residues. Oxidation of N-terminal Cys is decisive for further enzymatic modification of various neo–N termini by arginylation that generates potentially neofunctionalized or instable proteoforms. Here, I focus on the posttranslational modifications that are encompassed by protein degradation via the Cys/Arg branch of the N-degron pathway—part of the PROTEOLYSIS 6 (PRT6)/N-degron pathway—as well as the underlying physiological principles of this branch and its biological significance in stress response.
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The Scope, Functions, and Dynamics of Posttranslational Protein Modifications
Vol. 70 (2019), pp. 119–151More LessAssessing posttranslational modification (PTM) patterns within protein molecules and reading their functional implications present grand challenges for plant biology. We combine four perspectives on PTMs and their roles by considering five classes of PTMs as examples of the broader context of PTMs. These include modifications of the N terminus, glycosylation, phosphorylation, oxidation, and N-terminal and protein modifiers linked to protein degradation. We consider the spatial distribution of PTMs, the subcellular distribution of modifying enzymes, and their targets throughout the cell, and we outline the complexity of compartmentation in understanding of PTM function. We also consider PTMs temporally in the context of the lifetime of a protein molecule and the need for different PTMs for assembly, localization, function, and degradation. Finally, we consider the combined action of PTMs on the same proteins, their interactions, and the challenge ahead of integrating PTMs into an understanding of protein function in plants.
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Look Closely, the Beautiful May Be Small: Precursor-Derived Peptides in Plants
Vol. 70 (2019), pp. 153–186More LessDuring the past decade, a flurry of research focusing on the role of peptides as short- and long-distance signaling molecules in plant cell communication has been undertaken. Here, we focus on peptides derived from nonfunctional precursors, and we address several key questions regarding peptide signaling. We provide an overview of the regulatory steps involved in producing a biologically active peptide ligand that can bind its corresponding receptor(s) and discuss how this binding and subsequent activation lead to specific cellular outputs. We discuss different experimental approaches that can be used to match peptide ligands with their receptors. Lastly, we explore how peptides evolved from basic signaling units regulating essential processes in plants to more complex signaling systems as new adaptive traits developed and how nonplant organisms exploit this signaling machinery by producing peptide mimics.
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Next-Gen Approaches to Flavor-Related Metabolism
Vol. 70 (2019), pp. 187–212More LessAlthough flavor is an essential element for consumer acceptance of food, breeding programs have focused primarily on yield, leading to significant declines in flavor for many vegetables. The deterioration of flavor quality has concerned breeders; however, the complexity of this trait has hindered efforts to improve or even maintain it. Recently, the integration of flavor-associated metabolic profiling with other omics methodologies derived from big data has become a prominent trend in this research field. Here, we provide an overview of known metabolites contributing to flavor in the major vegetables as well as genetic analyses of the relevant metabolic pathways based on different approaches, especially multi-omics. We present examples demonstrating how omics analyses can help us to understand the accomplishments of historical flavor breeding practices and implement further improvements. The integration of genetics, cultivation, and postharvest practices with genome-scale data analyses will create enormous potential for further flavor quality improvements.
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Heterotrimeric G-Protein Signaling in Plants: Conserved and Novel Mechanisms
Vol. 70 (2019), pp. 213–238More LessHeterotrimeric GTP-binding proteins are key regulators of a multitude of signaling pathways in all eukaryotes. Although the core G-protein components and their basic biochemistries are broadly conserved throughout evolution, the regulatory mechanisms of G proteins seem to have been rewired in plants to meet specific needs. These proteins are currently the focus of intense research in plants due to their involvement in many agronomically important traits, such as seed yield, organ size regulation, biotic and abiotic stress responses, symbiosis, and nitrogen use efficiency. The availability of massive sequence information from a variety of plant species, extensive biochemical data generated over decades, and impressive genetic resources for plant G proteins have made it possible to examine their role, unique properties, and novel regulation. This review focuses on some recent advances in our understanding of the mechanistic details of this critical signaling pathway to enable the precise manipulation and generation of plants to meet future needs.
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Division Plane Establishment and Cytokinesis
Vol. 70 (2019), pp. 239–267More LessPlant cells divide their cytoplasmic content by forming a new membrane compartment, the cell plate, via a rerouting of the secretory pathway toward the division plane aided by a dynamic cytoskeletal apparatus known as the phragmoplast. The phragmoplast expands centrifugally and directs the cell plate to the preselected division site at the plasma membrane to fuse with the parental wall. The division site is transiently decorated by the cytoskeletal preprophase band in preprophase and prophase, whereas a number of proteins discovered over the last decade reside continuously at the division site and provide a lasting spatial reference for phragmoplast guidance. Recent studies of membrane fusion at the cell plate have revealed the contribution of functionally conserved eukaryotic proteins to distinct stages of cell plate biogenesis and emphasize the coupling of cell plate formation with phragmoplast expansion. Together with novel findings concerning preprophase band function and the setup of the division site, cytokinesis and its spatial control remain an open-ended field with outstanding and challenging questions to resolve.
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Control of Meristem Size
Vol. 70 (2019), pp. 269–291More LessA fascinating feature of plant growth and development is that plants initiate organs continually throughout their lifespan. The ability to do this relies on specialized groups of pluripotent stem cells termed meristems, which allow for the elaboration of the shoot, root, and vascular systems. We now have a deep understanding of the genetic networks that control meristem initiation and stem cell maintenance, including the roles of receptors and their ligands, transcription factors, and integrated hormonal and chromatin control. This review describes these networks and discusses how this knowledge is being applied to improve crop productivity by increasing fruit size and seed number.
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The Dynamics of Cambial Stem Cell Activity
Vol. 70 (2019), pp. 293–319More LessStem cell populations in meristematic tissues at distinct locations in the plant body provide the potency of continuous plant growth. Primary meristems, at the apices of the plant body, contribute mainly to the elongation of the main plant axes, whereas secondary meristems in lateral positions are responsible for the thickening of these axes. The stem cells of the vascular cambium—a secondary lateral meristem—produce the secondary phloem (bast) and secondary xylem (wood). The sites of primary and secondary growth are spatially separated, and mobile signals are expected to coordinate growth rates between apical and lateral stem cell populations. Although the underlying mechanisms have not yet been uncovered, it seems likely that hormones, peptides, and mechanical cues orchestrate primary and secondary growth. In this review, we highlight the current knowledge and recent discoveries of how cambial stem cell activity is regulated, with a focus on mobile signals and the response of cambial activity to environmental and stress factors.
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Thermomorphogenesis
Vol. 70 (2019), pp. 321–346More LessWhen exposed to warmer, nonstressful average temperatures, some plant organs grow and develop at a faster rate without affecting their final dimensions. Other plant organs show specific changes in morphology or development in a response termed thermomorphogenesis. Selected coding and noncoding RNA, chromatin features, alternative splicing variants, and signaling proteins change their abundance, localization, and/or intrinsic activity to mediate thermomorphogenesis. Temperature, light, and circadian clock cues are integrated to impinge on the level or signaling of hormones such as auxin, brassinosteroids, and gibberellins. The light receptor phytochrome B (phyB) is a temperature sensor, and the phyB–PHYTOCHROME-INTERACTING FACTOR 4 (PIF4)–auxin module is only one thread in a complex network that governs temperature sensitivity. Thermomorphogenesis offers an avenue to search for climate-smart plants to sustain crop and pasture productivity in the context of global climate change.
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Leaf Senescence: Systems and Dynamics Aspects
Vol. 70 (2019), pp. 347–376More LessLeaf senescence is an important developmental process involving orderly disassembly of macromolecules for relocating nutrients from leaves to other organs and is critical for plants’ fitness. Leaf senescence is the response of an intricate integration of various environmental signals and leaf age information and involves a complex and highly regulated process with the coordinated actions of multiple pathways. Impressive progress has been made in understanding how senescence signals are perceived and processed, how the orderly degeneration process is regulated, how the senescence program interacts with environmental signals, and how senescence regulatory genes contribute to plant productivity and fitness. Employment of systems approaches using omics-based technologies and characterization of key regulators have been fruitful in providing newly emerging regulatory mechanisms. This review mainly discusses recent advances in systems understanding of leaf senescence from a molecular network dynamics perspective. Genetic strategies for improving the productivity and quality of crops are also described.
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Molecular Mechanisms of Plant Regeneration
Vol. 70 (2019), pp. 377–406More LessPlants reprogram somatic cells following injury and regenerate new tissues and organs. Upon perception of inductive cues, somatic cells often dedifferentiate, proliferate, and acquire new fates to repair damaged tissues or develop new organs from wound sites. Wound stress activates transcriptional cascades to promote cell fate reprogramming and initiate new developmental programs. Wounding also modulates endogenous hormonal responses by triggering their biosynthesis and/or directional transport. Auxin and cytokinin play pivotal roles in determining cell fates in regenerating tissues and organs. Exogenous application of these plant hormones enhances regenerative responses in vitro by facilitating the activation of specific developmental programs. Many reprogramming regulators are epigenetically silenced during normal development but are activated by wound stress and/or hormonal cues.
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Functional Status of Xylem Through Time
Vol. 70 (2019), pp. 407–433More LessWater transport in vascular plants represents a critical component of terrestrial water cycles and supplies the water needed for the exchange of CO2 in the atmosphere for photosynthesis. Yet, many fundamental principles of water transport are difficult to assess given the scale and location of plant xylem. Here we review the mechanistic principles that underpin long-distance water transport in vascular plants, with a focus on woody species. We also discuss the recent development of noninvasive tools to study the functional status of xylem networks in planta. Limitations of current methods to detect drought-induced xylem blockages (e.g., embolisms) and quantify corresponding declines in sap flow, and the coordination of hydraulic dysfunction with other physiological processes are assessed. Future avenues of research focused on cross-validation of plant hydraulics methods are discussed, as well as a proposed fundamental shift in the theory and methodology used to characterize and measure plant water use.
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Molecular Networks of Seed Size Control in Plants
Vol. 70 (2019), pp. 435–463More LessThe size of seeds affects not only evolutionary fitness but also grain yield of crops. Understanding the mechanisms controlling seed size has become an important research field in plant science. Seed size is determined by the integrated signals of maternal and zygotic tissues, which control the coordinated growth of the embryo, endosperm, and seed coat. Recent advances have identified several signaling pathways that control seed size through maternal tissues, including or involving the ubiquitin-proteasome pathway, G-protein signaling, mitogen-activated protein kinase (MAPK) signaling, phytohormone perception and homeostasis, and some transcriptional regulators. Meanwhile, growth of the zygotic tissues is regulated in part by the HAIKU (IKU) pathway and phytohormones. This review provides a general overview of current findings in seed size control and discusses the emerging molecular mechanisms and regulatory networks found to be involved.
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Molecular and Environmental Regulation of Root Development
Vol. 70 (2019), pp. 465–488More LessIn order to optimally establish their root systems, plants are endowed with several mechanisms to use at distinct steps during their development. In this review, we zoom in on the major processes involved in root development and detail important new insights that have been generated in recent studies, mainly using the Arabidopsis root as a model. First, we discuss new insights in primary root development with the characterization of tissue-specific transcription factor complexes and the identification of non-cell-autonomous control mechanisms in the root apical meristem. Next, root branching is discussed by focusing on the earliest steps in the development of a new lateral root and control of its postemergence growth. Finally, we discuss the impact of phosphate, nitrogen, and water availability on root development and summarize current knowledge about the major molecular mechanisms involved.
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MicroRNAs and Their Regulatory Roles in Plant–Environment Interactions
Xianwei Song, Yan Li, Xiaofeng Cao, and Yijun QiVol. 70 (2019), pp. 489–525More LessMicroRNAs (miRNAs) are 20–24 nucleotide noncoding RNAs abundant in plants and animals. The biogenesis of plant miRNAs involves transcription of miRNA genes, processing of primary miRNA transcripts by DICER-LIKE proteins into mature miRNAs, and loading of mature miRNAs into ARGONAUTE proteins to form miRNA-induced silencing complex (miRISC). By targeting complementary sequences, miRISC negatively regulates gene expression, thereby coordinating plant development and plant–environment interactions. In this review, we present and discuss recent updates on the mechanisms and regulation of miRNA biogenesis, miRISC assembly and actions as well as the regulatory roles of miRNAs in plant developmental plasticity, abiotic/biotic responses, and symbiotic/parasitic interactions. Finally, we suggest future directions for plant miRNA research.
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Molecular Interactions Between Plants and Insect Herbivores
Vol. 70 (2019), pp. 527–557More LessDiverse molecular processes regulate the interactions between plants and insect herbivores. Here, we review genes and proteins that are involved in plant–herbivore interactions and discuss how their discovery has structured the current standard model of plant–herbivore interactions. Plants perceive damage-associated and, possibly, herbivore-associated molecular patterns via receptors that activate early signaling components such as Ca2+, reactive oxygen species, and MAP kinases. Specific defense reprogramming proceeds via signaling networks that include phytohormones, secondary metabolites, and transcription factors. Local and systemic regulation of toxins, defense proteins, physical barriers, and tolerance traits protect plants against herbivores. Herbivores counteract plant defenses through biochemical defense deactivation, effector-mediated suppression of defense signaling, and chemically controlled behavioral changes. The molecular basis of plant–herbivore interactions is now well established for model systems. Expanding molecular approaches to unexplored dimensions of plant–insect interactions should be a future priority.
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A Molecular View of Plant Local Adaptation: Incorporating Stress-Response Networks
Vol. 70 (2019), pp. 559–583More LessEcological specialization in plants occurs primarily through local adaptation to different environments. Local adaptation is widely thought to result in costly fitness trade-offs that result in maladaptation to alternative environments. However, recent studies suggest that such trade-offs are not universal. Further, there is currently a limited understanding of the molecular mechanisms responsible for fitness trade-offs associated with adaptation. Here, we review the literature on stress responses in plants to identify potential mechanisms underlying local adaptation and ecological specialization. We focus on drought, high and low temperature, flooding, herbivore, and pathogen stresses. We then synthesize our findings with recent advances in the local adaptation and plant molecular biology literature. In the process, we identify mechanisms that could cause fitness trade-offs and outline scenarios where trade-offs are not a necessary consequence of adaptation. Future studies should aim to explicitly integrate molecular mechanisms into studies of local adaptation.
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Evolution of Glucosinolate Diversity via Whole-Genome Duplications, Gene Rearrangements, and Substrate Promiscuity
Vol. 70 (2019), pp. 585–604More LessOver several decades, glucosinolates have become a model system for the study of specialized metabolic diversity in plants. The near-complete identification of biosynthetic enzymes, regulators, and transporters has provided support for the role of gene duplication and subsequent changes in gene expression, protein function, and substrate specificity as the evolutionary bases of glucosinolate diversity. Here, we provide examples of how whole-genome duplications, gene rearrangements, and substrate promiscuity potentiated the evolution of glucosinolate biosynthetic enzymes, regulators, and transporters by natural selection. This in turn may have led to the repeated evolution of glucosinolate metabolism and diversity in higher plants.
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Comparative and Functional Algal Genomics
Vol. 70 (2019), pp. 605–638More LessOver 100 whole-genome sequences from algae are published or soon to be published. The rapidly increasing availability of these fundamental resources is changing how we understand one of the most diverse, complex, and understudied groups of photosynthetic eukaryotes. Genome sequences provide a window into the functional potential of individual algae, with phylogenomics and functional genomics as tools for contextualizing and transferring knowledge from reference organisms into less well-characterized systems. Remarkably, over half of the proteins encoded by algal genomes are of unknown function, highlighting the volume of functional capabilities yet to be discovered. In this review, we provide an overview of publicly available algal genomes, their associated protein inventories, and their quality, with a summary of the statuses of protein function understanding and predictions.
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The Genomics of Oryza Species Provides Insights into Rice Domestication and Heterosis
Vol. 70 (2019), pp. 639–665More LessHere, we review recent progress in genetic and genomic studies of the diversity of Oryza species. In recent years, unlocking the genetic diversity of Oryza species has provided insights into the genomics of rice domestication, heterosis, and complex traits. Genome sequencing and analysis of numerous wild rice (Oryza rufipogon) and Asian cultivated rice (Oryza sativa) accessions have enabled the identification of genome-wide signatures of rice domestication and the unlocking of the origin of Asian cultivated rice. Moreover, similar studies on genome variations of African rice (Oryza glaberrima) cultivars and their closely related wild progenitor Oryza barthii accessions have provided strong evidence to support a theory of independent domestication in African rice. Integrated genomic approaches have efficiently investigated many heterotic loci in hybrid rice underlying yield heterosis advantages and revealed the genomic architecture of rice heterosis. We conclude that in-depth unlocking of genetic variations among Oryza species will further enhance rice breeding.
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CRISPR/Cas Genome Editing and Precision Plant Breeding in Agriculture
Vol. 70 (2019), pp. 667–697More LessEnhanced agricultural production through innovative breeding technology is urgently needed to increase access to nutritious foods worldwide. Recent advances in CRISPR/Cas genome editing enable efficient targeted modification in most crops, thus promising to accelerate crop improvement. Here, we review advances in CRISPR/Cas9 and its variants and examine their applications in plant genome editing and related manipulations. We highlight base-editing tools that enable targeted nucleotide substitutions and describe the various delivery systems, particularly DNA-free methods, that have linked genome editing with crop breeding. We summarize the applications of genome editing for trait improvement, development of techniques for fine-tuning gene regulation, strategies for breeding virus resistance, and the use of high-throughput mutant libraries. We outline future perspectives for genome editing in plant synthetic biology and domestication, advances in delivery systems, editing specificity, homology-directed repair, and gene drives. Finally, we discuss the challenges and opportunities for precision plant breeding and its bright future in agriculture.
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Risk Assessment and Regulation of Plants Modified by Modern Biotechniques: Current Status and Future Challenges
Vol. 70 (2019), pp. 699–726More LessThis review describes the current status and future challenges of risk assessment and regulation of plants modified by modern biotechniques, namely genetic engineering and genome editing. It provides a general overview of the biosafety and regulation of genetically modified plants and details different regulatory frameworks with a focus on the European situation. The environmental risk and safety assessment of genetically modified plants is explained, and aspects of toxicological assessments are discussed, especially the controversial debate in Europe on the added scientific value of untargeted animal feeding studies. Because RNA interference (RNAi) is increasingly explored for commercial applications, the risk and safety assessment of RNAi-based genetically modified plants is also elucidated. The production, detection, and identification of genome-edited plants are described. Recent applications of modern biotechniques, namely synthetic biology and gene drives, are discussed, and a short outlook on the future follows.
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Crop Biodiversity: An Unfinished Magnum Opus of Nature
Vol. 70 (2019), pp. 727–751More LessCrop biodiversity is one of the major inventions of humanity through the process of domestication. It is also an essential resource for crop improvement to adapt agriculture to ever-changing conditions like global climate change and consumer preferences. Domestication and the subsequent evolution under cultivation have profoundly shaped the genetic architecture of this biodiversity. In this review, we highlight recent advances in our understanding of crop biodiversity. Topics include the reduction of genetic diversity during domestication and counteracting factors, a discussion of the relationship between parallel phenotypic and genotypic evolution, the role of plasticity in genotype × environment interactions, and the important role subsistence farmers play in actively maintaining crop biodiversity and in participatory breeding. Linking genotype and phenotype remains the holy grail of crop biodiversity studies.
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Crop Improvement Through Temperature Resilience
Vol. 70 (2019), pp. 753–780More LessAbnormal environmental temperature affects plant growth and threatens crop production. Understanding temperature signal sensing and the balance between defense and development in plants lays the foundation for improvement of temperature resilience. Here, we summarize the current understanding of cold signal perception/transduction as well as heat stress response. Dissection of plant responses to different levels of cold stresses (chilling and freezing) illustrates their common and distinct signaling pathways. Axillary bud differentiation in response to chilling is presented as an example of the trade-off between defense and development. Vernalization is a cold-dependent development adjustment mediated by O-GlcNAcylation and phosphorylation to sense long-term cold. Recent progress on major quantitative trait loci genes for heat tolerance has been summarized. Molecular mechanisms in utilizing temperature-sensitive sterility in super hybrid breeding in China are revealed. The way to improve crop temperature resilience using integrative knowledge of omics as well as systemic and synthetic biology, especially the molecular module program, is summarized.
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Water Use Efficiency as a Constraint and Target for Improving the Resilience and Productivity of C3 and C4 Crops
Vol. 70 (2019), pp. 781–808More LessThe ratio of plant carbon gain to water use, known as water use efficiency (WUE), has long been recognized as a key constraint on crop production and an important target for crop improvement. WUE is a physiologically and genetically complex trait that can be defined at a range of scales. Many component traits directly influence WUE, including photosynthesis, stomatal and mesophyll conductances, and canopy structure. Interactions of carbon and water relations with diverse aspects of the environment and crop development also modulate WUE. As a consequence, enhancing WUE by breeding or biotechnology has proven challenging but not impossible. This review aims to synthesize new knowledge of WUE arising from advances in phenotyping, modeling, physiology, genetics, and molecular biology in the context of classical theoretical principles. In addition, we discuss how rising atmospheric CO2 concentration has created and will continue to create opportunities for enhancing WUE by modifying the trade-off between photosynthesis and transpiration.
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A Fruitful Journey: Pollen Tube Navigation from Germination to Fertilization
Vol. 70 (2019), pp. 809–837More LessIn flowering plants, pollen tubes undergo tip growth to deliver two nonmotile sperm to the ovule where they fuse with an egg and central cell to achieve double fertilization. This extended journey involves rapid growth and changes in gene activity that manage compatible interactions with at least seven different cell types. Nearly half of the genome is expressed in haploid pollen, which facilitates genetic analysis, even of essential genes. These unique attributes make pollen an ideal system with which to study plant cell–cell interactions, tip growth, cell migration, the modulation of cell wall integrity, and gene expression networks. We highlight the signaling systems required for pollen tube navigation and the potential roles of Ca2+ signals. The dynamics of pollen development make sexual reproduction highly sensitive to heat stress. Understanding this vulnerability may generate strategies to improve seed crop yields that are under threat from climate change.
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Previous Volumes
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Volume 75 (2024)
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Volume 74 (2023)
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Volume 73 (2022)
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Volume 72 (2021)
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Volume 71 (2020)
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Volume 70 (2019)
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Volume 69 (2018)
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Volume 68 (2017)
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Volume 67 (2016)
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Volume 66 (2015)
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Volume 65 (2014)
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Volume 64 (2013)
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Volume 63 (2012)
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Volume 62 (2011)
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Volume 61 (2010)
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Volume 60 (2009)
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Volume 59 (2008)
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Volume 58 (2007)
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Volume 57 (2006)
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Volume 56 (2005)
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Volume 55 (2004)
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Volume 54 (2003)
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Volume 53 (2002)
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Volume 52 (2001)
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Volume 51 (2000)
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Volume 50 (1999)
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Volume 49 (1998)
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Volume 48 (1997)
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Volume 47 (1996)
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Volume 46 (1995)
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Volume 45 (1994)
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Volume 44 (1993)
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Volume 43 (1992)
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Volume 42 (1991)
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Volume 41 (1990)
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Volume 40 (1989)
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Volume 39 (1988)
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Volume 38 (1987)
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Volume 37 (1986)
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Volume 36 (1985)
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Volume 35 (1984)
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Volume 34 (1983)
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Volume 33 (1982)
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Volume 32 (1981)
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Volume 31 (1980)
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Volume 30 (1979)
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Volume 29 (1978)
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Volume 28 (1977)
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Volume 27 (1976)
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Volume 26 (1975)
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Volume 25 (1974)
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Volume 24 (1973)
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Volume 23 (1972)
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Volume 22 (1971)
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Volume 21 (1970)
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Volume 20 (1969)
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Volume 19 (1968)
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Volume 18 (1967)
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Volume 17 (1966)
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Volume 16 (1965)
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Volume 15 (1964)
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Volume 14 (1963)
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Volume 13 (1962)
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Volume 12 (1961)
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Volume 11 (1960)
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Volume 10 (1959)
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Volume 9 (1958)
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Volume 8 (1957)
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Volume 7 (1956)
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Volume 6 (1955)
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Volume 5 (1954)
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Volume 4 (1953)
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Volume 3 (1952)
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Volume 2 (1951)
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Volume 1 (1950)
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Volume 0 (1932)