AP1G mediates vacuolar acidification during synergid-controlled pollen tube reception

Arabidopsis class A S-acyl transferases modify the pollen receptors LIP1 and PRK1 to regulate pollen tube guidance

Protein S-acylation catalyzed by protein S-acyl transferases (PATs) is a reversible lipid modification regulating protein targeting, stability, and interaction profiles. PATs are encoded by large gene families in plants, and many proteins including receptor-like cytoplasmic kinases (RLCKs) and receptor-like kinases (RLKs) are subject to S-acylation. However, few PATs have been assigned substrates, and few S-acylated proteins have known upstream enzymes. We report that Arabidopsis (Arabidopsis thaliana) class A PATs redundantly mediate pollen tube guidance and participate in the S-acylation of POLLEN RECEPTOR KINASE1 (PRK1) and LOST IN POLLEN TUBE GUIDANCE1 (LIP1), a critical RLK or RLCK for pollen tube guidance, respectively. PAT1, PAT2, PAT3, PAT4, and PAT8, collectively named PENTAPAT for simplicity, are enriched in pollen and show similar subcellular distribution. Functional loss of PENTAPAT reduces seed set due to male gametophytic defects. Specifically, pentapat pollen tubes are compromised in directional growth. We determine that PRK1 and LIP1 interact with PENTAPAT, and their S-acylation is reduced in pentapat pollen. The plasma membrane (PM) association of LIP1 is reduced in pentapat pollen, whereas point mutations reducing PRK1 S-acylation affect its affinity with its interacting proteins. Our results suggest a key role of S-acylation in pollen tube guidance through modulating PM receptor complexes.

Arabidopsis HAPLESS13/AP-1µ is critical for pollen sac formation and tapetal function

The production of excess and viable pollen grains is critical for reproductive success of flowering plants. Pollen grains are produced within anthers, the male reproductive organ whose development involves precisely controlled cell differentiation, division, and intercellular communication. In Arabidopsis thaliana, specification of an archesporial cell (AC) at four corners of a developing anther, followed by programmed cell divisions, generates four pollen sacs, walled by four cell layers among which the tapetum is in close contact with developing microspores. Tapetum secretes callose-dissolving enzymes to release microspores at early stages and undergoes programmed cell death (PCD) to deliver nutrients and signals for microspore development at later stages. Except for transcription factors, plasma membrane (PM)-associated and secretory peptides have also been demonstrated to mediate anther development. Adaptor protein complexes (AP) recruit both cargos and coat proteins during vesicle trafficking. Arabidopsis AP-1µ/HAPLESS13 (HAP13) is a core component of AP-1 for protein sorting at the trans-Golgi network/early endosomes (TGN/EE). We report here that Arabidopsis HAP13 is critical for pollen sac formation and for sporophytic control of pollen production. Functional loss of HAP13 causes a reduction in pollen sac number. It also results in the dysfunction of tapetum such that secretory function of tapetum at early stages and PCD of tapetum at later stages are both compromised. We further show that the expression of SPL, the polar distribution of auxin maximum, as well as the asymmetric distribution of PIN1 are interfered in hap13 anthers, which in combination may lead to male sterility in hap13.

Killing me softly - Programmed cell death in plant reproduction from sporogenesis to fertilization

Regulated or programmed cell death (RCD or PCD) is a fundamental biological principle integral to a considerable variety of functions in multicellular organisms. In plants, different PCD processes are part of biotic and abiotic stress responses, but also occur as an essential aspect of unperturbed plant development. PCD is particularly abundant during plant reproduction, eliminating unwanted or no longer needed cells, tissues, or organs in a precisely controlled manner. Failure in reproductive PCD can have detrimental consequences for plant reproduction. Here we shed a light on the latest research into PCD mechanisms in plant reproduction from sex determination over sporogenesis to pollination and fertilization.

Regulation of pollen tube growth by cellular pH and ions

Tip growth of the pollen tube is a model system for the study of cell polarity establishment in flowering plants. The tip growth of the pollen tube displays an oscillating pattern corresponding to cellular ion and pH dynamics. Therefore, cellular pH and ions play an important role in pollen growth and development. In this review, we summarized the current advances in understanding the function of cellular pH and ions in regulating pollen tube growth. We analyzed the physiological roles and underlying mechanisms of cellular pH and ions, including Ca²⁺, K⁺, and Cl^-, in regulating pollen tube growth. We further examined the function of Ca²⁺ in regulating cytoskeletons, small G proteins, and cell wall development in relation to pollen tube growth. We also examined the regulatory roles of cellular pH in pollen tube growth as well as pH regulation of ion flow, cell wall development, auxin signaling, and cytoskeleton function in pollen. In addition, we assessed the regulation of pollen tube growth by proton pumps and the maintenance of pH homeostasis in the trans-Golgi network by ion transporters. The interplay of ion homeostasis and pH dynamics was also assessed. We discussed the unanswered questions regarding pollen tube growth that need to be addressed in the future.

AP1/2β-mediated exocytosis of tapetum-specific transporters is required for pollen development in Arabidopsis thaliana

AP-1 and AP-2 adaptor protein (AP) complexes mediate clathrin-dependent trafficking at the trans-Golgi network (TGN) and the plasma membrane, respectively. Whereas AP-1 is required for trafficking to plasma membrane and vacuoles, AP-2 mediates endocytosis. These AP complexes consist of four subunits (adaptins): two large subunits (β1 and γ for AP-1 and β2 and α for AP-2), a medium subunit μ, and a small subunit σ. In general, adaptins are unique to each AP complex, with the exception of β subunits that are shared by AP-1 and AP-2 in some invertebrates. Here, we show that the two putative Arabidopsis thaliana AP1/2β adaptins co-assemble with both AP-1 and AP-2 subunits and regulate exocytosis and endocytosis in root cells, consistent with their dual localization at the TGN and plasma membrane. Deletion of both β adaptins is lethal in plants. We identified a critical role of β adaptins in pollen wall formation and reproduction, involving the regulation of membrane trafficking in the tapetum and pollen germination. In tapetal cells, β adaptins localize almost exclusively to the TGN and mediate exocytosis of the plasma membrane transporters such as ATP-binding cassette (ABC)G9 and ABCG16. This study highlights the essential role of AP1/2β adaptins in plants and their specialized roles in specific cell types.

AP1G2 Affects Mitotic Cycles of Female and Male Gametophytes in Arabidopsis

During sexual reproduction in flowering plants, haploid spores are formed from meiosis of spore mother cells. The spores then undergo mitosis, develop into female and male gametophytes, and give rise to seeds after fertilization. We identified a female sterile mutant ap1g2-4 from EMS mutagenesis, and analyses of two T-DNA insertion mutants, ap1g2-1 ^+/- and ap1g2-3 ^-/-, and detected a partial female and male sterility. The ap1g2 mutant gametophyte development was arrested at one nuclear stage. A complementation test using a genomic sequence of AP1G2 with its native promoter restored the function in the three ap1g2 mutant lines. Transcriptome profiling of ap1g2 ovules revealed that four genes encoding clathrin assembly proteins PICALM5A/B and PICALM9A/B, which were involved in endocytosis, were downregulated, which were confirmed to interact with AP1G2 through yeast two-hybrid assays and BIFC analysis. Our result also demonstrated that RALFL4-8-15-19-26 CML16 and several calcium-dependent protein kinases, including CPK14-16-17, were all downregulated in the ovules of ap1g2-1 ^+/-. Moreover, Ca²⁺ concentration was low in impaired gametophytes. Therefore, we proposed that through interaction with PICALM5A/B and PICALM9A/B, AP1G2 may mediate gametogenesis accompanied by Ca²⁺ signaling in Arabidopsis. Our findings revealed a crucial role of AP1G2 in female and male gametogenesis in Arabidopsis and enhanced our understanding of the molecular mechanisms underpinning sexual reproduction in flowering plants.

ADAPTOR PROTEIN-1 complex-mediated post-Golgi trafficking is critical for pollen wall development in Arabidopsis

Primexine deposition is essential for the formation of pollen wall patterns and is precisely regulated by the tapetum and microspores. While tapetum- and/or microspore-localized proteins are required for primexine biosynthesis, how their trafficking is established and controlled is poorly understood. In Arabidopsis thaliana, AP1σ1 and AP1σ2, two genes encoding the σ subunit of the trans-Golgi network/early endosome (TGN/EE)-localized ADAPTOR PROTEIN-1 complex (AP-1), are partially redundant for plant viability, and the loss of AP1σ1 function reduces male fertility due to defective primexine formation. Here, we investigated the role of AP-1 in pollen wall formation. The deposition of Acyl-CoA SYNTHETASE5 (ACOS5) and type III LIPID TRANSFER PROTEINs (LTPs) secreted from the anther tapetum, which are involved in exine formation, were impaired in ap1σ1 mutants. In addition, the microspore plasma membrane (PM) protein RUPTURED POLLEN GRAIN1 (RPG1), which regulates primexine deposition, accumulated abnormally at the TGN/EE in ap1σ1 mutants. We show that AP-1μ recognizes the YXXΦ motif of RPG1, thereby regulating its PM abundance through endocytic trafficking, and that loss of AP1σ1 decreases the levels of other AP-1 subunits at the TGN/EE. Our observations show that AP-1-mediated post-Golgi trafficking plays a vital role in pollen wall development by regulating protein transport in tapetal cells and microspores.

Plant endosomes as protein sorting hubs

Endocytosis, secretion, and endosomal trafficking are key cellular processes that control the composition of the plasma membrane. Through the coordination of these trafficking pathways, cells can adjust the composition, localization, and turnover of proteins and lipids in response to developmental or environmental cues. Upon being incorporated into vesicles and internalized through endocytosis, plant plasma membrane proteins are delivered to the trans-Golgi network (TGN). At the TGN, plasma membrane proteins are recycled back to the plasma membrane or transferred to multivesicular endosomes (MVEs), where they are further sorted into intralumenal vesicles for degradation in the vacuole. Both types of plant endosomes, TGN and MVEs, act as sorting organelles for multiple endocytic, recycling, and secretory pathways. Molecular assemblies such as retromer, ESCRT (endosomal sorting complex required for transport) machinery, small GTPases, adaptor proteins, and SNAREs associate with specific domains of endosomal membranes to mediate different sorting and membrane-budding events. In this review, we discuss the mechanisms underlying the recognition and sorting of proteins at endosomes, membrane remodeling and budding, and their implications for cellular trafficking and physiological responses in plants.

Arabidopsis RAN GTPases are critical for mitosis during male and female gametogenesis

The development of male and female gametophytes is a prerequisite for successful propagation of angiosperms. The small GTPases RAN play fundamental roles in numerous cellular processes. Although RAN GTPases have been characterized in plants, their roles in cellular processes are far from understood. We report here that RAN GTPases in Arabidopsis are critical for gametophytic development. RAN1 loss-of-function showed no defects in gametophytic development likely due to redundancy. However, the expression of a dominant negative or constitutively active RAN1 resulted in gametophytic lethality. Genetic interference of RAN GTPases caused the arrest of pollen mitosis I and of mitosis of functional megaspores, implying a key role of properly regulated RAN activity in mitosis during gametophytic development.

Current progress in plant V-ATPase: From biochemical properties to physiological functions

Vacuolar-type adenosine triphosphatase (V-ATPase, VHA) is a highly conserved, ATP-driven multisubunit proton pump that is widely distributed in all eukaryotic cells. V-ATPase consists of two domains formed by at least 13 different subunits, the membrane peripheral V₁ domain responsible for ATP hydrolysis, and the membrane-integral V₀ domain responsible for proton translocation. V-ATPase plays an essential role in energizing secondary active transport and is indispensable to plants. In addition to multiple stress responses, plant V-ATPase is also implicated in physiological processes such as growth, development, and morphogenesis. Based on the identification of distinct V-ATPase mutants and advances in luminal pH measurements in vivo, it has been revealed that this holoenzyme complex plays a pivotal role in pH homeostasis of the plant endomembrane system and endocytic and secretory trafficking. Here, we review recent progress in comprehending the biochemical properties and physiological functions of plant V-ATPase and explore the topics that require further elucidation.

The canonical α-SNAP is essential for gametophytic development in Arabidopsis

The development of male and female gametophytes is a pre-requisite for successful reproduction of angiosperms. Factors mediating vesicular trafficking are among the key regulators controlling gametophytic development. Fusion between vesicles and target membranes requires the assembly of a fusogenic soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs) complex, whose disassembly in turn ensures the recycle of individual SNARE components. The disassembly of post-fusion SNARE complexes is controlled by the AAA+ ATPase N-ethylmaleimide-sensitive factor (Sec18/NSF) and soluble NSF attachment protein (Sec17/α-SNAP) in yeast and metazoans. Although non-canonical α-SNAPs have been functionally characterized in soybeans, the biological function of canonical α-SNAPs has yet to be demonstrated in plants. We report here that the canonical α-SNAP in Arabidopsis is essential for male and female gametophytic development. Functional loss of the canonical α-SNAP in Arabidopsis results in gametophytic lethality by arresting the first mitosis during gametogenesis. We further show that Arabidopsis α-SNAP encodes two isoforms due to alternative splicing. Both isoforms interact with the Arabidopsis homolog of NSF whereas have distinct subcellular localizations. The presence of similar alternative splicing of human α-SNAP indicates that functional distinction of two α-SNAP isoforms is evolutionarily conserved.

The Arabidopsis R-SNARE protein YKT61 is essential for gametophyte development

Gametophyte development is a pre-requisite for plant reproduction and seed yield; therefore, studies of gametophyte development help us understand fundamental biological questions and have potential applications in agriculture. The biogenesis and dynamics of endomembrane compartments are critical for cell survival, and their regulatory mechanisms are just beginning to be revealed. Here, we report that the Arabidopsis thaliana SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) protein YKT61 is essential for both male and female gametogenesis. By using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-based genome editing, we demonstrated that male and female gametophytes carrying YKT61 loss-of-function alleles do not survive. Specifically, loss of YKT61 function resulted in the arrest of male gametophytic development at pollen mitosis I and the degeneration of female gametophytes. A three-base-pair deletion in YKT61 in the ykt61-3 mutant resulted in a single-amino acid deletion in the longin domain of YKT61; the resulting mutant protein does not interact with multiple SNAREs and showed substantially reduced membrane association, suggesting that the N-terminal longin domain of YKT61 plays multiple roles in its function. This study demonstrates that Arabidopsis YKT61 is essential for male and female gametogenesis and sets an example for functional characterization of essential genes with the combination of Cas9-mediated editing and expression from a Cas9-resistant transgene.

Cargo sorting zones in the trans-Golgi network visualized by super-resolution confocal live imaging microscopy in plants

The trans-Golgi network (TGN) has been known as a key platform to sort and transport proteins to their final destinations in post-Golgi membrane trafficking. However, how the TGN sorts proteins with different destinies still remains elusive. Here, we examined 3D localization and 4D dynamics of TGN-localized proteins of Arabidopsis thaliana that are involved in either secretory or vacuolar trafficking from the TGN, by a multicolor high-speed and high-resolution spinning-disk confocal microscopy approach that we developed. We demonstrate that TGN-localized proteins exhibit spatially and temporally distinct distribution. VAMP721 (R-SNARE), AP (adaptor protein complex)-1, and clathrin which are involved in secretory trafficking compose an exclusive subregion, whereas VAMP727 (R-SNARE) and AP-4 involved in vacuolar trafficking compose another subregion on the same TGN. Based on these findings, we propose that the single TGN has at least two subregions, or "zones", responsible for distinct cargo sorting: the secretory-trafficking zone and the vacuolar-trafficking zone.

The regulatory framework of developmentally programmed cell death in floral organs: A review

Developmentally programmed cell death (dPCD) is a tightly controlled biological process. In recent years, vital roles of dPCD on regulating floral organ growth and development have been reported. It is well known that flower is an essential organ for reproduction and a turning point of plants' life cycle. Hence, uncovering the complex molecular networks which regulates dPCD processes in floral organs is utmost important. So far, our understanding of dPCD on floral organ growth and development is just starting. Herein, we summarize the important factors that involved in the tapetal degeneration, pollen tube rupture, receptive synergid cell death, nucellar degradation, and antipodal cell degradation. Meanwhile, the known factors that involved in transmitting tract formation and self-incompatibility-induced PCD were also introduced. Furthermore, the genes that associated with anther dehiscence and petal senescence and abscission were reviewed as well. The functions of various types of factors involved in floral dPCD processes are highlighted principally. The regulatory panorama described here can provide us some insights about flower-specific dPCD process.

Transcriptional Regulation of PLETHORA1 in the Root Meristem Through an Importin and Its Two Antagonistic Cargos

Plant roots are sustained through meristem activity at the root tip. Two transcriptional pathways, one mediated by PLETHORAs (PLTs) and the other by SHORTROOT and SCARECROW, play major roles in root meristem development. The role of PLTs during root meristem development requires a concentration gradient, which is not only contributed by posttranslational regulation such as growth dilution and intercellular movement but also likely by a largely unknown fine-tuned transcriptional regulatory mechanism. We report here that Arabidopsis (Arabidopsis thaliana) JANUS positively regulates PLT1 expression in the root meristem by recruiting RNA polymerase II (Pol II) to PLT1 and by interacting with PLT1. JANUS-dependent recruitment of Pol II is inhibited through the competitive binding of JANUS by GRF-INTERACTING FACTOR1 (GIF1)/ANGUSTIFOLIA3, a transcriptional cofactor that negatively regulates PLT1 expression. Finally, GIF1 and JANUS, the antagonistic regulators of PLT1, both depend on Arabidopsis IMPORTIN β4 for their nuclear accumulation. The combination of an importin and its two antagonistic cargos in PLT1 transcription may have logistic benefits in fine-tuning the transcription of PLT1 in root meristem.

Comparative transcriptome analysis provides insights into the molecular mechanism underlying double fertilization between self-crossed Solanum melongena and that hybridized with Solanum aethiopicum

Wild relatives represent a source of variation for many traits of interest for eggplant (Solanum melongena) breeding, as well as for broadening its genetic base. However, interspecific hybridization with wild relatives has been barely used in eggplant breeding programs, and reproductive barriers have resulted in reduced seed numbers in interspecific combinations. The mechanism underlying this phenomenon remains unclear. We hybridized females of cultivated eggplant 177 (Solanum melongena) with males of wild relatives 53 and Y11 (Solanum aethiopicum). Self-crossed 177 was the control. The seed number per control fruit was significantly higher than that of the hybrids. Paraffin sections showed no significant difference between control and 177×53 and 177×Y11. Double fertilization began 4 days post-pollination. Sperm cells were fused with egg cells 6 days post-pollination. To understand the differences in molecular mechanisms underlying this process, transcriptomes of ovaries at 0, 4, and 6 days after self-crossing and hybridization were analyzed. We screened 22,311 differentially expressed genes (DEGs) between the control and hybrids 4 and 6 days post-pollination. A total of 497 DEGs were shared among all pollination combinations. These DEGs were enriched in plant hormone transduction, cell senescence, metabolism, and biosynthesis pathways. DEG clustering analysis indicated distinct expression patterns between the control and hybrids but not between the hybrids. The DEGs in hybrids involved secondary metabolic process, phenylpropanoid metabolic process, and carboxypeptidase activity, while those in the control involved xyloglucan metabolic process, auxin-activated signaling pathway, cell wall polysaccharide metabolic process, and xyloglucosyl transferase activity. Additionally, 1683 transcription factors, including members of the AP2-ERF, MYB, bHLH, and B3 families may play important roles in self-crossing and hybridization. Our results provide insights into the regulatory mechanisms underlying variations between ovaries of self-crossed and hybrid eggplants and a basis for future studies on crossbreeding Solanum and genetic mechanisms underlying double fertilization.

Vacuole Biogenesis in Plants: How Many Vacuoles, How Many Models?

Vacuoles are the largest membrane-bounded organelles and have essential roles in plant growth and development, but several important questions on the biogenesis and dynamics of lytic vacuoles (LVs) remain. Here, we summarize and discuss recent research and models of vacuole formation, and propose, with testable hypotheses, that besides inherited vacuoles, plant cells can also synthesize LVs de novo from multiple organelles and routes in response to growth and development or external factors. Therefore, LVs may be further classified into different subgroups and/or populations with different pH, cargos, and functions, among which multivesicular body (MVB)-derived small vacuoles are the main source for central vacuole formation in arabidopsis root cortical cells.

Arabidopsis KETCH1 Is Critical for the Nuclear Accumulation of Ribosomal Proteins and Gametogenesis

Male and female gametophytes are generated from micro- or megaspore mother cells through consecutive meiotic and mitotic cell divisions. Defects in these divisions often result in gametophytic lethality. Gametophytic lethality was also reported when genes encoding ribosome-related proteins were mutated. Although numerous ribosomal proteins (RPs) have been identified in plants based on homology with their yeast and metazoan counterparts, how RPs are regulated, e.g., through dynamic subcellular targeting, is unknown. We report here that an Arabidopsis (Arabidopsis thaliana) importin β, KETCH1 (karyopherin enabling the transport of the cytoplasmic HYL1), is critical for gametogenesis. Karyopherins are molecular chaperones mediating nucleocytoplasmic protein transport. However, the role of KETCH1 during gametogenesis is independent of HYPONASTIC LEAVES 1 (HYL1), a previously reported KETCH1 cargo. Instead, KETCH1 interacts with several RPs and is critical for the nuclear accumulation of RPL27a, whose mutations caused similar gametophytic defects. We further showed that knocking down KETCH1 caused reduced ribosome biogenesis and translational capacity, which may trigger the arrest of mitotic cell cycle progression and lead to gametophytic lethality.

Insights into secrets along the pollen tube pathway in need to be discovered

The process of plant fertilization provides an outstanding example of refined control of gene expression. During this elegant process, subtle communication occurs between neighboring cells, based on chemical signals, that induces cellular mechanisms of patterning and growth. Having faced an immediate issue of self-incompatibility responses, the pathway to fertilization starts once the stigmatic cells recognize a compatible pollen grain, and it continues with numerous players interacting to affect pollen tube growth and the puzzling process of navigation along the transmitting tract. The pollen tube goes through a guidance process that begins with a preovular stage (i.e. prior to the influence of the target ovule), with interactions with factors from the transmitting tissue. In the subsequent ovular-guidance stage a specific relationship develops between the pollen tube and its target ovule. This stage is divided into the funicular and micropylar guidance steps, with numerous receptors working in signalling cascades. Finally, just after the pollen tube has passed beyond the synergids, fusion of the gametes occurs and the developing seed-the ultimate aim of the process-will start to mature. In this paper, we review the existing knowledge of the crucial biological processes involved in pollen-pistil interactions that give rise to the new seed.

Friend or foe: Signaling mechanisms during double fertilization in flowering seed plants

Since the first description of double fertilization 120 years ago, the processes of pollen tube growth and guidance, sperm cell release inside the receptive synergid cell, as well as fusion of two sperm cells to the female gametes (egg and central cell) have been well documented in many flowering plants. Especially microscopic techniques, including live cell imaging, were used to visualize these processes. Molecular as well as genetic methods were applied to identify key players involved. However, compared to the first 11 decades since its discovery, the past decade has seen a tremendous advancement in our understanding of the molecular mechanisms regulating angiosperm fertilization. Whole signaling networks were elucidated including secreted ligands, corresponding receptors, intracellular interaction partners, and further downstream signaling events involved in the cross-talk between pollen tubes and their cargo with female reproductive cells. Biochemical and structural biological approaches are now increasingly contributing to our understanding of the different signaling processes required to distinguish between compatible and incompatible interaction partners. Here, we review the current knowledge about signaling mechanisms during above processes with a focus on the model plants Arabidopsis thaliana and Zea mays (maize). The analogy that many of the identified "reproductive signaling mechanisms" also act partly or fully in defense responses and/or cell death is also discussed.

Multilayered signaling pathways for pollen tube growth and guidance

Sexual reproductive success is essential for the survival of all higher organisms. As the most prosperous and diverse group of land plants on earth, flowering plants evolved highly sophisticated fertilization mechanisms. To adapt to the terrestrial environment, a tubular structure pollen tube has been evolved to deliver the immobile sperm cells to the egg and central cell enclosed within the ovule. The pollen tube is generated from the vegetative cell of the pollen (male gametophyte), where two sperm cells are hosted. Pollen tube elongation in the maternal tissue and navigation to the ovule require intimate cell-cell interactions between the tube and female tissues. Questions on how the single-celled pollen tube accomplishes such task and how the female tissues accommodate the tube have attracted many plant biologists. Here, we review recent progresses and concepts in understanding the molecular mechanisms governing pollen tube growth and its interactions with the female tissues. We will also discuss the future perspective in this field.

Chemical signaling for pollen tube guidance at a glance

Pollen tube guidance is a unique navigating system that is required for the successful sexual reproduction of plants. As plant sperm cells are non-motile and egg cells are embedded deep inside the female tissues, a pollen tube delivers the two sperm cells that it contains by growing towards the ovule, in which the egg cell resides. Pollen tube growth towards the ovule is precisely controlled and divided into two stages, preovular and ovular guidance. In this Cell Science at a Glance article and accompanying poster, we provide a comprehensive overview of pollen tube guidance and highlight some of the attractant peptides used during ovular guidance. We further discuss the precise one-to-one guidance system that exists in multi-ovular plants. The pollen tube-blocking system, which is mediated by male–female crosstalk communication, to avoid attraction of multiple pollen tubes, is also reviewed.