Evolution of development of pollen performance

Genetic diversity in male and female landraces of teasel gourd in north-eastern India and strategies for crop improvement through induced monocliny

BACKGROUND

Teasel gourd is an important, indigenous, vegetatively propagated, high-value, underutilized cucurbit vegetable crop grown in South and Southeast Asia. Due to its wider adaptability, it is grown from plains to mid-hills. The crop is lacking in research, primarily related to the extent of genetic diversity in the region and crop improvement, which is further constrained by dioecism. To assess the genetic diversity in male and female populations of teasel gourd based on morphological traits and microsatellite makers and the response of AgNO3 to induce monocliny, seventy genotypes, including eight males, were collected from different regions of the Northeastern states of India.

RESULTS

Under evaluation trials, wider variability was observed for leaf, flower, and fruit characteristics. Traits: ovary length ranged from 0.58 to 1.23 cm, fruit length 4.76 to 11.23 cm, fruit diameter 3.0 to 3.13 cm, fruit weight 22.8 to 129.3 g, and 100 seed weights 12.60 to 36.3 g, reducing sugar 2.99 to 7.39%, and vitamin-C content from 44.80 to 79.68 mg/100 g. The fruits and quality attributes have also shown high heritability (> 60%) and genetic advance (> 20%). Under molecular analysis, out of 43 microsatellite markers, 40 were polymorphic, and the polymorphism information content (PIC) ranged from 0.08 (Sed-09) to 0.68 (McSSR-5). A moderate genetic diversity was observed in the male and female genotypes based on gene diversity, PIC, and Nei's genetic distance. The additive main effects and multiplicative interaction (AMMI) analysis of variance for fruit traits has shown a significantly higher contribution of the genotype, followed by the genotype × environment interaction. Based on multi-trait stability index analysis for fruit traits, genotypes MNTGC-2, MNTGC-1, MNTGC-4, MZTGC-1, and ASTGC-3 were the most stable. Foliar application of AgNO3 at 500 mg l- 1 was best for inducing hermaphroditism in female genotypes. The pollen germination can be enhanced to 82.3% over the control (23.1%) by the application of nutrient media comprised of sucrose (15%), boric acid (25 mg l- 1), and calcium nitrate (25 mg l- 1).

CONCLUSIONS

The available diverse genetic resources in teasel gourd can be effectively utilized by selecting stable superior genotypes, crop multiplication by selfing in superior induced hermaphrodite genotypes and exploiting heterosis by mating among diverse genotypes using silver nitrate.

Phylogeny does not predict the outcome of heterospecific pollen-pistil interactions in a species-rich alpine plant community

PREMISE

Co-occurring plant species that share generalist pollinators often exchange pollen. This heterospecific pollen transfer (HPT) impacts male and female reproductive success through pollen loss and reductions in seed set, respectively. The resulting fitness cost of HPT imposes selection on reproductive traits (e.g., floral color and shape), yet we currently lack strong predictors for the post-pollination fate of heterospecific pollen, especially within community and phylogenetic contexts.

METHODS

We investigated the fate of heterospecific pollen at three distinct stages of plant reproduction: (1) pollen germination on the stigma, (2) pollen tube growth in the style, and (3) fertilization of ovules. We experimentally crossed 11 naturally co-flowering species in the subalpine meadows of the Colorado Rocky Mountains, across a spectrum of phylogenetic relatedness. Using generalized linear mixed models and generalized linear models, we evaluated the effect of parental species identity and phylogenetic relatedness on pollen tube growth at each reproductive stage.

RESULTS

We found that heterospecific pollen tubes can germinate and grow within pistils at each reproductive stage, even when parental species are >100 My divergent. There was no significant effect of phylogenetic distance on heterospecific pollen success, and no evidence for a mechanism that suspends heterospecific pollen germination or pollen tube growth within heterospecific stigmas or styles.

CONCLUSIONS

Our results show that even in communities where HPT is common, pre-zygotic post-pollination mechanisms do not provide strong barriers to interspecific fertilization. HPT can result in the loss of ovules even between highly diverged plant species.

Male secreted short glycoproteins link sperm competition to the reproductive isolation of species

Sperm competition is found across multicellular organisms1,2,3,4 using both external and internal fertilization.5,6 Sperm competition and post-copulatory cryptic female choice can promote incompatibility between species due to the antagonistic coevolution of the sexes within a species.7,8,9,10,11 This between-species incompatibility is accelerated and markedly asymmetrical when sexual mode differs, producing the "weak inbreeder, strong outcrosser" (WISO) pattern.12 Here, we show that male secreted short (MSS) sperm glycoproteins of nematodes constitute a gametic effector of WISO. In obligately outcrossing Caenorhabditis, MSS is dispensable for baseline fertility but required for intraspecific sperm competitiveness.13 MSS is lost in self-fertile lineages, likely as a response to selection for a hermaphrodite-biased sex ratio.14 Selfing hermaphrodites that mate with males of closely related outcrossing species are rapidly sterilized due to ovarian sperm invasion.11 The simplification of the male proteome in selfing species suggests that many factors could contribute to invasivity.13,15,16 However, restoration of just MSS to the self-fertile C. briggsae is sufficient to induce mild invasivity. Further, MSS+ sperm appear to derive their competitive advantage from this behavior, directly linking interspecies incompatibility with intraspecific competition. MSS-related proteins (MSRPs) remaining in the C. briggsae genome are similar in structure, expression, and localization to MSS but are not necessary for normal sperm competitiveness. Further, overexpression of the MSRP most similar to MSS, Cbr-MSRP-3, is insufficient to enhance competitiveness. We conclude that outcrossing species retain sperm competition factors that contribute to their reproductive isolation from selfing relatives that lost them.

Exploring the influences of resource limitation and plant aging on pollen development in Azorella nivalis Phil. (Apiaceae), a long-lived high-Andean cushion plant

Angiosperm pollen, the male gametophyte, plays a crucial role in facilitating fertilization by protecting and transporting male sperm cells to the female pistil. Despite their seemingly simple structure, pollen grains undergo intricate development to produce viable sperm cells capable of fertilizing the egg cell. Factors such as resource limitation and plant aging can disrupt normal pollen development and affect pollen performance. We investigated the influence of plant resources and aging on pollen developmental failure in Azorella nivalis Phil., an exceptionally long-lived high-Andean species that grows in a stressful alpine environment. Leveraging the modular nature of plants, we aimed to identify intra-individual sources of variation in pollen developmental failure. By using pollen viability and variation in viable pollen grain size as indicators of pollen developmental performance, we assessed whether proxies of plant resource availability and aging influenced these pollen traits at the inter-individual, inter-flower and intra-flower levels. Our findings revealed decreased pollen viability in putative resource-depleted flowers and in shoots that experienced higher levels of meristematic divisions from the zygote (i.e., greater cell depth). Additionally, we observed increased variability in the size of viable pollen grains in resource-depleted anthers. Our study suggests that resource availability and shoot aging are critical determinants shaping pollen development in long-lived plants at the intra-individual level. These findings contribute to our understanding of how differences in male fitness can arise in plants, with implications for their evolutionary trajectory.

Cryopreservation of two-celled pollen: a model system for studying the cellular mechanisms of cryoinjury and recovery

Cryopreservation serves as an invaluable technique for safeguarding the genetic diversity of plants and various organisms, while also facilitating fundamental biological research. Despite notable advancements in this field, the cryopreservation of certain cell types and tissues remains challenging, particularly those that exhibit sensitivity to low temperatures. Two-celled pollen is a promising model system for the study of cryopreservation. By exploring the cryopreservation of two-celled pollen, deeper insights can be gained into the cellular and molecular mechanisms of cryoinjury and recovery. This knowledge can be used to develop new and improved cryopreservation protocols for a wider range of cell types and tissues. It is relatively simple, consisting of only two cells, and it is relatively easy to cryopreserve and culture. In addition to its potential for improving cryopreservation technologies, the study of two-celled pollen cryopreservation can also shed light on fundamental biological processes such as cell division, development, and stress tolerance. By unlocking the mysteries of two-celled pollen cryopreservation, we can gain a deeper understanding of nature's inner workings. This article reviews examples of studies that have successfully used two-celled pollen cryopreservation, highlighting key findings and discoveries enabled by this technique as case studies.

Heat stress: Pollen tubes ROSted by heat stress

Male gametophyte development is highly sensitive to elevated temperatures. A new study identifies potential drivers of reproductive thermoresilience during pollen tube growth by comparing a set of thermotolerant and thermosensitive tomato cultivars.

Positive selection and relaxed purifying selection contribute to rapid evolution of male-biased genes in a dioecious flowering plant

Sex-biased genes offer insights into the evolution of sexual dimorphism. Sex-biased genes, especially those with male bias, show elevated evolutionary rates of protein sequences driven by positive selection and relaxed purifying selection in animals. Although rapid sequence evolution of sex-biased genes and evolutionary forces have been investigated in animals and brown algae, less is known about evolutionary forces in dioecious angiosperms. In this study, we separately compared the expression of sex-biased genes between female and male floral buds and between female and male flowers at anthesis in dioecious Trichosanthes pilosa (Cucurbitaceae). In floral buds, sex-biased gene expression was pervasive, and had significantly different roles in sexual dimorphism such as physiology. We observed higher rates of sequence evolution for male-biased genes in floral buds compared to female-biased and unbiased genes. Male-biased genes under positive selection were mainly associated with functions to abiotic stress and immune responses, suggesting that high evolutionary rates are driven by adaptive evolution. Additionally, relaxed purifying selection may contribute to accelerated evolution in male-biased genes generated by gene duplication. Our findings, for the first time in angiosperms, suggest evident rapid evolution of male-biased genes, advance our understanding of the patterns and forces driving the evolution of sexual dimorphism in dioecious plants.

The sporophyte-to-gametophyte transition: The haploid generation comes of age

Flowering plants alternate between two multicellular generations: the diploid sporophyte and haploid gametophyte. Despite its small size, the gametophyte has significant impacts on plant genetics, evolution, and breeding. Each male pollen grain and female embryo sac is a multicellular organism with independent gene expression, a functioning metabolism, and specialized cell types. In this review, we describe recent progress in understanding the process in which the haploid genome takes over expression from its diploid parent - the sporophyte-to-gametophyte transition. The focus is on pollen, but similar concepts may also apply to the female gametophyte. Technological advances in single-cell genomics offer the opportunity to characterize haploid gene expression in unprecedented detail, positioning the field to make rapid progress.

Nectar bacteria stimulate pollen germination and bursting to enhance microbial fitness

Many organisms consume pollen, yet mechanisms of its digestion remain a fundamental enigma in pollination biology,^1-3 as pollen is protected by a recalcitrant outer shell.^4-8 Pollen is commonly found in floral nectar,^9,10 as are nectar microbes, which are nearly ubiquitous among flowers.^11-13 Nectar specialist bacteria, like Acinetobacter, can reach high densities (up to 10⁹ cells/mL), despite the fact that floral nectar is nitrogen poor.^14-17 Here, we show evidence that the genus Acinetobacter, prevalent nectar- and bee-associated bacteria,^12,18-20 can induce pollen germination and bursting, gain access to protoplasm nutrients, and thereby grow to higher densities. Although induced germination had been suggested as a potential method in macroscopic pollen consumers,^2,21-23 and fungal inhibition of pollen germination has been shown,^24-27 direct biological induction of germination has not been empirically documented outside of plants.^28-32Acinetobacter pollinis SCC477¹⁹ induced over 5× greater pollen germination and 20× greater pollen bursting than that of uninoculated pollen by 45 min. When provided with germinable pollen, A. pollinis stimulates protein release and grows to nearly twice the density compared to growth with ungerminable pollen, indicating that stimulation of germination benefits bacterial fitness. In contrast, a common nectar-inhabiting yeast (Metschnikowia)³³ neither induced nor benefited from pollen germination. We conclude that Acinetobacter both specifically causes and benefits from inducing pollen germination and bursting. Further study of microbe-pollen interactions may inform many aspects of pollination ecology, including floral microbial ecology,^34,35 pollinator nutrient acquisition from pollen,^2,3,21,36 and cues of pollen germination for plant reproduction.^37-39.

A Compendium of in vitro Germination Media for Pollen Research

The correct choice of in vitro pollen germination media (PGM) is crucial in basic and applied pollen research. However, the methodological gaps (e.g., strong focus of current research on model species and cultivated plants along with the lack of general rules for developing a PGM) makes experimenting with pollen difficult. We closed these gaps by compiling a compendium of optimized in vitro PGM recipes from more than 1800 articles published in English, German, and Russian from 1926 to 2019. The compendium includes 1572 PGM recipes successfully used to germinate pollen grains or produce pollen tubes in 816 species representing 412 genera and 114 families (both monocots and dicots). Among the 110 components recorded from the different PGM recipes, sucrose (89% of species), H₃BO₃ (77%), Ca²⁺ (59%), Mg²⁺ (44%), and K⁺ (39%) were the most commonly used PGM components. PGM pH was reported in 35% of all studies reviewed. Also, we identified some general rules for creating PGM for various groups of species differing in area of research (wild and cultivated species), phylogenetic relatedness (angiosperms vs. gymnosperms, dicots vs. monocots), pollen physiology (bi- and tri-cellular), biochemistry (starchy vs. starchless pollen grains), and stigma properties (dry vs. wet), and compared the component requirements. Sucrose, calcium, and magnesium concentrations were significantly different across most categories indicating that pollen sensitivity to sugar and mineral requirements in PGM is highly group-specific and should be accounted for when composing new PGM. This compendium is an important data resource on PGM and can facilitate future pollen research.

Reproduction Multitasking: The Male Gametophyte

The gametophyte represents the sexual phase in the alternation of generations in plants; the other, nonsexual phase is the sporophyte. Here, we review the evolutionary origins of the male gametophyte among land plants and, in particular, its ontogenesis in flowering plants. The highly reduced male gametophyte of angiosperm plants is a two- or three-celled pollen grain. Its task is the production of two male gametes and their transport to the female gametophyte, the embryo sac, where double fertilization takes place. We describe two phases of pollen ontogenesis-a developmental phase leading to the differentiation of the male germline and the formation of a mature pollen grain and a functional phase representing the pollen tube growth, beginning with the landing of the pollen grain on the stigma and ending with double fertilization. We highlight recent advances in the complex regulatory mechanisms involved, including posttranscriptional regulation and transcript storage, intracellular metabolic signaling, pollen cell wall structure and synthesis, protein secretion, and phased cell-cell communication within the reproductive tissues.

For things to stay the same, things must change: polyploidy and pollen tube growth rates

BACKGROUND AND AIMS

Pollen tube growth rate (PTGR) is an important single-cell performance trait that may evolve rapidly under haploid selection. Angiosperms have experienced repeated cycles of polyploidy (whole genome duplication), and polyploidy has cell-level phenotypic consequences arising from increased bulk DNA amount and numbers of genes and their interactions. We sought to understand potential effects of polyploidy on several underlying determinants of PTGR - pollen tube dimensions and construction rates - by comparing diploid-polyploid near-relatives in Betula (Betulaceae) and Handroanthus (Bignoniaceae).

METHODS

We performed intraspecific, outcrossed hand-pollinations on pairs of flowers. In one flower, PTGR was calculated from the longest pollen tube per time of tube elongation. In the other, styles were embedded in glycol methacrylate, serial-sectioned in transverse orientation, stained and viewed at 1000× to measure tube wall thicknesses (W) and circumferences (C). Volumetric growth rate (VGR) and wall production rate (WPR) were then calculated for each tube by multiplying cross-sectional tube area (πr2) or wall area (W × C), by the mean PTGR of each maternal replicate respectively.

KEY RESULTS

In Betula and Handroanthus, the hexaploid species had significantly wider pollen tubes (13 and 25 %, respectively) and significantly higher WPRs (22 and 18 %, respectively) than their diploid congeners. PTGRs were not significantly different in both pairs, even though wider polyploid tubes were predicted to decrease PTGRs by 16 and 20 %, respectively.

CONCLUSIONS

The larger tube sizes of polyploids imposed a substantial materials cost on PTGR, but polyploids also exhibited higher VGRs and WPRs, probably reflecting the evolution of increased metabolic activity. Recurrent cycles of polyploidy followed by genome reorganization may have been important for the evolution of fast PTGRs in angiosperms, involving a complex interplay between correlated changes in ploidy level, genome size, cell size and pollen tube energetics.

High expression in maize pollen correlates with genetic contributions to pollen fitness as well as with coordinated transcription from neighboring transposable elements

In flowering plants, gene expression in the haploid male gametophyte (pollen) is essential for sperm delivery and double fertilization. Pollen also undergoes dynamic epigenetic regulation of expression from transposable elements (TEs), but how this process interacts with gene expression is not clearly understood. To explore relationships among these processes, we quantified transcript levels in four male reproductive stages of maize (tassel primordia, microspores, mature pollen, and sperm cells) via RNA-seq. We found that, in contrast with vegetative cell-limited TE expression in Arabidopsis pollen, TE transcripts in maize accumulate as early as the microspore stage and are also present in sperm cells. Intriguingly, coordinate expression was observed between highly expressed protein-coding genes and their neighboring TEs, specifically in mature pollen and sperm cells. To investigate a potential relationship between elevated gene transcript level and pollen function, we measured the fitness cost (male-specific transmission defect) of GFP-tagged coding sequence insertion mutations in over 50 genes identified as highly expressed in the pollen vegetative cell, sperm cell, or seedling (as a sporophytic control). Insertions in seedling genes or sperm cell genes (with one exception) exhibited no difference from the expected 1:1 transmission ratio. In contrast, insertions in over 20% of vegetative cell genes were associated with significant reductions in fitness, showing a positive correlation of transcript level with non-Mendelian segregation when mutant. Insertions in maize gamete expressed2 (Zm gex2), the sole sperm cell gene with measured contributions to fitness, also triggered seed defects when crossed as a male, indicating a conserved role in double fertilization, given the similar phenotype previously demonstrated for the Arabidopsis ortholog GEX2. Overall, our study demonstrates a developmentally programmed and coordinated transcriptional activation of TEs and genes in pollen, and further identifies maize pollen as a model in which transcriptomic data have predictive value for quantitative phenotypes.

Reproductive ecology and postpollination development in the hydrophilous monocot Ruppia maritima

PREMISE

Water-pollination (hydrophily) is a rare but important pollination mechanism that has allowed angiosperms to colonize marine and aquatic habitats. Hydrophilous plants face unique reproductive challenges, and many have evolved characteristic pollen traits and pollination strategies that may have downstream consequences for pollen performance. However, little is known about reproductive development in the life history stage between pollination and fertilization (the progamic phase) in hydrophilous plants. The purpose of this study was to characterize reproductive ecology and postpollination development in water-pollinated Ruppia maritima L.

METHODS

Naturally pollinated inflorescences of R. maritima were collected from the field. Experimental pollinations using both putatively outcross and self pollen were conducted in the greenhouse and inflorescences were collected at appropriate intervals after pollination. Pollen reception, pollen germination, pollen tube growth, and carpel morphology were characterized.

RESULTS

Ruppia maritima exhibits incomplete protogyny, allowing for delayed selfing. Pollen germinated within 15 min after pollination. The average shortest possible pollen tube pathway was 425 μm and pollen tubes first reached the ovule at 45 min after pollination. The mean adjusted pollen tube growth rate was 551 μm/h.

CONCLUSIONS

Ruppia pollen is adapted for rapid pollen germination, which is likely advantageous in an aquatic habitat. Small effective pollen loads suggest that pollen competition intensity is low. Selection for traits such as a long period of stigma receptivity, fast pollen germination, and carpel morphology likely played a larger role in shaping postpollination reproductive development in Ruppia than evolution in pollen tube growth rates.

Pollen competition is the mechanism underlying a variety of evolutionary phenomena in dioecious plants

It has long been known that more pollen grains often arrive on stigmas than there are ovules to fertilize, resulting in pollen competition. Moreover, this competition among pollen grains (gametophytes) depends, in part, on their extensive haploid gene expression. Here I review how this leads to a variety of phenomena in dioecious plants of interest to evolutionary biologists. For example, pollen competition can lead to extreme female-biased sex ratios. In addition, gene expression by individual pollen grains can slow mutation accumulation and degeneration of the Y chromosome. Lastly, I review work on how the haploid selection resulting from pollen competition has been proposed to influence which alleles are linked to the Y chromosome, and some recent empirical evidence in support of this theory.

How does genome size affect the evolution of pollen tube growth rate, a haploid performance trait?

PREMISE

Male gametophytes of most seed plants deliver sperm to eggs via a pollen tube. Pollen tube growth rates (PTGRs) of angiosperms are exceptionally rapid, a pattern attributed to more effective haploid selection under stronger pollen competition. Paradoxically, whole genome duplication (WGD) has been common in angiosperms but rare in gymnosperms. Pollen tube polyploidy should initially accelerate PTGR because increased heterozygosity and gene dosage should increase metabolic rates. However, polyploidy should also independently increase tube cell size, causing more work which should decelerate growth. We asked how genome size changes have affected the evolution of seed plant PTGRs.

METHODS

We assembled a phylogenetic tree of 451 species with known PTGRs. We then used comparative phylogenetic methods to detect effects of neo-polyploidy (within-genus origins), DNA content, and WGD history on PTGR, and correlated evolution of PTGR and DNA content.

RESULTS

Gymnosperms had significantly higher DNA content and slower PTGR optima than angiosperms, and their PTGR and DNA content were negatively correlated. For angiosperms, 89% of model weight favored Ornstein-Uhlenbeck models with a faster PTGR optimum for neo-polyploids, whereas PTGR and DNA content were not correlated. For within-genus and intraspecific-cytotype pairs, PTGRs of neo-polyploids < paleo-polyploids.

CONCLUSIONS

Genome size increases should negatively affect PTGR when genetic consequences of WGDs are minimized, as found in intra-specific autopolyploids (low heterosis) and gymnosperms (few WGDs). But in angiosperms, the higher PTGR optimum of neo-polyploids and non-negative PTGR-DNA content correlation suggest that recurrent WGDs have caused substantial PTGR evolution in a non-haploid state.

Pollen Developmental Arrest: Maintaining Pollen Fertility in a World With a Changing Climate

During evolution of land plants, the haploid gametophytic stage has been strongly reduced in size and the diploid sporophytic phase has become the dominant growth form. Both male and female gametophytes are parasitic to the sporophyte and reside in separate parts of the flower located either on the same plant or on different plants. For fertilization to occur, bi-cellular or tri-cellular male gametophytes (pollen grains) have to travel to the immobile female gametophyte in the ovary. To survive exposure to a hostile atmosphere, pollen grains are thought to enter a state of complete or partial developmental arrest (DA). DA in pollen is strongly associated with acquisition of desiccation tolerance (DT) to extend pollen viability during air travel, but occurrence of DA in pollen is both species-dependent and at the same time strongly dependent on the reigning environmental conditions at the time of dispersal. Several environmental stresses (heat, drought, cold, humidity) are known to affect pollen production and viability. Climate change is also posing a serious threat to plant reproductive behavior and crop productivity. It is therefore timely to gain a better understanding of how DA and pollen viability are controlled in plants and how pollen viability can be protected to secure crop yields in a changing environment. Here, we provide an overview of how DA and pollen viability are controlled and how the environment affects them. We make emphasis on what is known and areas where a deeper understanding is needed.

Functional identification of lncRNAs in sweet cherry (Prunus avium) pollen tubes via transcriptome analysis using single-molecule long-read sequencing

Sweet cherry (Prunus avium) is a popular fruit with high nutritional value and excellent flavor. Although pollen plays an important role in the double fertilization and subsequent fruit production of this species, little is known about its pollen tube transcriptome. In this study, we identified 16,409 transcripts using single-molecule sequencing. After filtering 292 transposable elements, we conducted further analyses including mRNA classification, gene function prediction, alternative splicing (AS) analysis, and long noncoding RNA (lncRNA) identification to gain insight into the pollen transcriptome. The filtered transcripts could be matched with 3,438 coding region sequences from the sweet cherry genome. GO and KEGG analyses revealed complex biological processes during pollen tube elongation. A total of 2043 AS events were predicted, 7 of which were identified in different organs, such as the leaf, pistil and pollen tube. Using BLASTnt and the Coding-Potential Assessment Tool (CPAT), we distinguished a total of 284 lncRNAs, among which 154 qualified as natural antisense transcripts (NATs). As the NATs could be the reverse complements of coding mRNA sequences, they might bind to coding sequences. Antisense transfection assays showed that the NATs could regulate the expression levels of their complementary sequences and even affect the growth conditions of pollen tubes. In summary, this research characterizes the transcripts of P. avium pollen and lays the foundation for elucidating the physiological and biochemical mechanisms underlying sexual reproduction in the male gametes of this species.

Evolution of Cell Wall Polymers in Tip-Growing Land Plant Gametophytes: Composition, Distribution, Functional Aspects and Their Remodeling

During evolution of land plants, the first colonizing species presented leafy-dominant gametophytes, found in non-vascular plants (bryophytes). Today, bryophytes include liverworts, mosses, and hornworts. In the first seedless vascular plants (lycophytes), the sporophytic stage of life started to be predominant. In the seed producing plants, gymnosperms and angiosperms , the gametophytic stage is restricted to reproduction. In mosses and ferns, the haploid spores germinate and form a protonema, which develops into a leafy gametophyte producing rhizoids for anchorage, water and nutrient uptakes. The basal gymnosperms (cycads and Ginkgo) reproduce by zooidogamy. Their pollen grains develop a multi-branched pollen tube that penetrates the nucellus and releases flagellated sperm cells that swim to the egg cell. The pollen grain of other gymnosperms (conifers and gnetophytes) as well as angiosperms germinates and produces a pollen tube that directly delivers the sperm cells to the ovule (siphonogamy). These different gametophytes, which are short or long-lived structures, share a common tip-growing mode of cell expansion. Tip-growth requires a massive cell wall deposition to promote cell elongation, but also a tight spatial and temporal control of the cell wall remodeling in order to modulate the mechanical properties of the cell wall. The growth rate of these cells is very variable depending on the structure and the species, ranging from very slow (protonemata, rhizoids, and some gymnosperm pollen tubes), to a slow to fast-growth in other gymnosperms and angiosperms. In addition, the structural diversity of the female counterparts in angiosperms (dry, semi-dry vs wet stigmas, short vs long, solid vs hollow styles) will impact the speed and efficiency of sperm delivery. As the evolution and diversity of the cell wall polysaccharides accompanied the diversification of cell wall structural proteins and remodeling enzymes, this review focuses on our current knowledge on the biochemistry, the distribution and remodeling of the main cell wall polymers (including cellulose, hemicelluloses, pectins, callose, arabinogalactan-proteins and extensins), during the tip-expansion of gametophytes from bryophytes, pteridophytes (lycophytes and monilophytes), gymnosperms and the monocot and eudicot angiosperms.