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The objective of this study was to characterize the reproductive compatibility among cultivars and selections of Japanese plum through controlled pollination, both in vivo and in situ, to obtain a profile of reproductively compatible cultivars. In situ and in vivo self-pollinations were carried out in an F1 population of Japanese plum, and in vivo pollinations were conducted on the pollen-grain receptor cultivars: Laetitia, Zafira and Fortune, and the pollen-grain donor cultivars: Piamontesa, Selection Plum 86-13, Harry Pickstone, Black Amber, Bruce, SC-17, Laetitia, SC-15, SC 7, Zafira, Amarelinha, América, Reubennel and Fortune, to verify the percentage of germination of pollen grains and growth of pollen tubes in the pistils of the recipient plants. The in situ and in vivo assays for the F1 population confirm the self-compatibility of genotypes 13 and 35. The Laetitia cultivar is self-incompatible; however, it is compatible with the Selection 'Plum 86-13'. 'Zafira' is self-incompatible. 'Fortune' is compatible with 'Amarelinha', 'SC-7', 'America', 'Harry Pickstone' and 'Reubennel', but it is self-incompatible. [ABSTRACT FROM AUTHOR]

In nature, the ability to avoid self-fertilization has evolved to prevent the deleterious effects of inbreeding. However, under cultivation conditions, self-incompatibility can reduce the pollination efficiency of Coffea canephora. The objective of this study was to characterize the self-incompatibility expression of the most cultivated genotypes in Western Amazonia, to improve the management of this coffee plant. In vitro pollinations were conducted among 45 genotypes, and the development of pollen tubes was evaluated using fluorescence microscopy. Pollination efficiency was evaluated considering the allelic variability within a breeding population from an ideal condition of maximum genetic variability. Based on the compatibility response, the genotypes were organized into six groups: group I (24.4%), group II (31.1%), group III (24.4%), group IV (2.2%), group V (2.2%), and group VI (15.6%). The lower frequencies of groups IV, V, and VI were associated with the lower frequency of the rarest allelic forms in this breeding population (p = 0.36, q = 0.26, r = 0.29, and s = 0.10). The correspondence between allelic and genotypic frequencies indicates that this population is in Hardy–Weinberg equilibrium (HWE) for this trait. Considering the cultivation of 2 to 10 clones, the population studied showed intermediate pollination efficiency between an ideal HWE population with p = q = r = s = 0.25 and a population with the rarest allelic forms (p = 0.48, q = 0.32, r = 0.19, s = 0.01). Efficiency estimates were stabilized from the cultivation of five clones, indicating that cultivating a minimum number of clones should be considered. Theoretically, maximum pollination efficiency is achieved by representing all alleles in equal proportions, whereas in practice, farmers should ensure the cultivation of plants from different compatibility groups, without significant imbalances. [ABSTRACT FROM AUTHOR]

Trendy high-density olive fields are often monovarietal orchards, mostly using the cultivar Arbequina. However, Arbequina shows a strong self-incompatibility response, and its yields depend on wind cross-pollination, which is not always available. With the aim of finding suitable self-compatible cultivars that can replace Arbequina, we evaluated pollen–pistil interaction, fruit set and seed paternity in Arbosana under different pollination treatments: self-pollination, open-pollination and three cross-pollination treatments: × Arbequina, × Sikitita and × Koroneiki. All these cultivars are low-vigor cultivars suitable for high-density orchards, making them potential pollinizers for Arbosana. The results show that Arbosana is also self-incompatible with a strong reduction in fruit set due to a lower fertilization level caused by a strong inhibition of pollen tube growth in self-pollinated flowers. Seed-paternity analyses confirmed the self-incompatibility response of Arbosana and suggest that some fruit obtained in bagged shoots under self-pollination were, in fact, a product of cross-fertilization. In conclusion, we recommend against the use of Arbosana in large monovarietal orchards. On the contrary, good results were obtained under cross-pollination with Sikitita, Arbequina and Koroneiki pollen, allowing us to recommend them as pollinizers for Arbosana in appropriate pollination designs. This is the first time Arbosana self-incompatibility has been reported. [ABSTRACT FROM AUTHOR]

This document provides a summary of a special issue on the ornamental industry, which covers a wide range of topics related to plant propagation, defense mechanisms, tissue culture, genetics in urban planning, and emerging trends in the ornamental plant market. The research was conducted by authors from various countries, highlighting the global relevance of the industry. The authors hope that readers will find inspiration for further research in this field. The ornamental industry is a diverse and segmented industry that focuses on growing and marketing plants and cut flowers for decorative purposes. The global flower and ornamental plants market was valued at $27 billion in 2021 and is expected to increase in value by 2029. The industry faces challenges such as limited resources, climate change, sustainable pest and disease management, diversification of supply, and optimization of marketing and distribution. Breeding plays a crucial role in developing new cultivars, and advancements in genomics and gene editing have shown promise. Efficient systems for propagation, cultivation, and marketing are also important for the industry's success. [Extracted from the article]

The European hazelnut (Corylus avellana L.) is a self-incompatible, wind-pollinated species of significant economic-productive interest, mainly cultivated between the Mediterranean basin and the Black Sea. Hazelnut breeding programs and high cropping in commercial orchards are necessarily linked to the availability of fertile pollen with wide germinability and high viability. The objective was to develop an improved method to determine the germinability of pollen, comparing the results with those found in the literature. Pollen germinability was firstly evaluated on a wild-type accession using boric acid (H3BO3), calcium nitrate (Ca(NO3)2), magnesium sulfate (MgSO4), potassium nitrate (KNO3), casein hydrolysate and different concentrations of sugars, including sucrose (10, 15 and 25%) and two monosaccharides, glucose (15%) and fructose (15%). The optimal composition included 15% sucrose in a semi-solid medium composed of 1% animal gelatin, containing collagen. This formulation was then tested on three cultivars of commercial interest, evaluating the effect of different concentrations of sucrose. The comparison between different in vitro germination methods showed that the hanging drop technique in a semi-solid medium provides a statistically higher germination index compared to the liquid and solid/agarized techniques. This study proposes an easy-to-use medium for the in vitro germination of Corylus avellana L. pollen. [ABSTRACT FROM AUTHOR]

Within flowers, the style channel receives pollen and transmits male gametes inside elongating pollen tubes to ovules. The styles of maize/corn are called silks. Fertilization-stage silks possess complex microbiomes, which may partially derive from pollen. These microbiomes lack functional analysis. We hypothesize that fertilization-stage silk microbiomes promote host fertilization to ensure their own vertical transmission. We further hypothesize that these microbes encode traits to survive stresses within the silk (water/nitrogen limitation) and pollen (dehydration/aluminum) habitats. Here, bacteria cultured from fertilization-stage silks of 14 North American maize genotypes underwent genome mining and functional testing, which revealed osmoprotection, nitrogen-fixation, and aluminum-tolerance traits. Bacteria contained auxin biosynthesis genes, and testing confirmed indole compound secretion, which is relevant, since pollen delivers auxin to silks to stimulate egg cell maturation. Some isolates encoded biosynthetic/transport compounds known to regulate pollen tube guidance/growth. The isolates encoded ACC deaminase, which degrades the precursor for ethylene that otherwise accelerates silk senescence. The findings suggest that members of the microbiome of fertilization-stage silks encode adaptations to survive the stress conditions of silk/pollen and have the potential to express signaling compounds known to impact reproduction. Overall, whereas these microbial traits have traditionally been assumed to primarily promote vegetative plant growth, this study proposes they may also play selfish roles during host reproduction. [ABSTRACT FROM AUTHOR]

n the Neotropics, the focus of apomictic studies predominantly centres on trees within the Brazilian savanna, characterized, mostly as sporophytic and facultative, associated with polyploidy and polyembryony. To enhance our understanding of the mechanisms governing apomixis and sexual reproduction in tropical herbaceous plants, we clarify the relationship between apomixis, chromosome counts, and polyembryony in the epiphytic orchid Zygopetalum mackayi , which forms a polyploid complex within rocky outcrops in both the Brazilian savanna and the Atlantic forest. To define embryo origins and describe megasporogenesis and megagametogenesis, we performed manual self-pollinations in first-day flowers of cultivated plants, considering all three cytotypes (2 x , 3 x , 4 x) of this species. Flowers and fruits at different stages were collected to describe the development and morphology of ovules and seeds considering sexual and apomictic processes. As self-pollination treatments resulted in high fruit abortion in diploids, we also examined pollen tube development in aborted flowers and fruits to search for putative anomalies. Megasporogenesis and megagametogenesis occur regularly in all cytotypes. Apomixis is facultative and sporophytic, and associated with polyploid cytotypes, while diploid individuals exclusively engage in sexual reproduction. Polyembryony is caused mainly by the production of adventitious embryos from nucellar cells of triploids and tetraploids, but also by the development of multiple archesporia in all cytotypes. Like other apomictic angiosperms within the Brazilian savanna, our findings demonstrate that apomixis in Z. mackayi relies on pollinators for seed production. We also consider the ecological implications of these apomictic patterns in Z. mackayi within the context of habitat loss and its dependence on pollinators. [ABSTRACT FROM AUTHOR]

In Brassicaceae self‐incompatibility (SI), self‐pollen rejection is initiated by the S‐haplotype specific interactions between the pollen S cysteine‐rich/S‐locus protein 11 (SCR/SP11) ligands and the stigma S receptor kinases (SRK). In Brassica SI, a member of the Plant U‐Box (PUB) E3 ubiquitin ligases, ARM‐repeat containing 1 (ARC1), is then activated by SRK in this stigma and cellular events downstream of this cause SI pollen rejection by inhibiting pollen hydration and pollen tube growth. During the transition to selfing, Arabidopsis thaliana lost the SI components, SCR, SRK, and ARC1. However, this trait can be reintroduced into A. thaliana by adding back functional copies of these genes from closely related SI species. Both SCR and SRK are required for this, though the degree of SI pollen rejection varies between A. thaliana accessions, and ARC1 is not always needed to produce a strong SI response. For the A. thaliana C24 accession, only transforming with Arabidopsis lyrataSCR and SRK confers a strong SI trait (SI‐C24), and so here, we investigated if ARC1‐related PUBs were involved in the SI pathway in the transgenic A. thaliana SI‐C24 line. Two close ARC1 homologs, PUB17 and PUB16, were selected, and (Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR‐associated protein 9 (Cas9) technology was used to generate pub17 and pub16 mutations in the C24 accession. These mutants were then crossed into the transgenic A. thaliana SI‐C24 line and their potential impact on SI pollen rejection was investigated. Overall, we did not observe any significant differences in SI responses to implicate PUB17 and PUB16 functioning in the transgenic A. thaliana SI‐C24 stigma to reject SI pollen. [ABSTRACT FROM AUTHOR]

Flowering plants rely on the polarized growth of pollen tubes to deliver sperm cells (SCs) to the embryo sac for double fertilization. In pollen, the vegetative nucleus (VN) and two SCs form the male germ unit (MGU). However, the mechanism underlying directional transportation of MGU is not well understood. In this study, we provide the first full picture of the dynamic interplay among microtubules, actin filaments, and MGU during pollen germination and tube growth. Depolymerization of microtubules and inhibition of kinesin activity result in an increased velocity and magnified amplitude of VN's forward and backward movement. Pharmacological washout experiments further suggest that microtubules participate in coordinating the directional movement of MGU. In contrast, suppression of the actomyosin system leads to a reduced velocity of VN mobility but without a moving pattern change. Moreover, detailed observation shows that the direction and velocity of VN's movement are in close correlations with those of the actomyosin-driven cytoplasmic streaming surrounding VN. Therefore, we propose that while actomyosin-based cytoplasmic streaming influences on the oscillational movement of MGU, microtubules and kinesins avoid MGU drifting with the cytoplasmic streaming and act as the major regulator for fine-tuning the proper positioning and directional migration of MGU in pollen. Male germ unit (MGU) transportation in pollen tubes is critical for double fertilization in flowering plants. Wang et al. reveal distinct functions of microtubule-kinesin and actomyosin system in the directional migration of MGU. [ABSTRACT FROM AUTHOR]

Lespedeza davurica (Laxm.) is a leguminous plant with significant ecological benefits, but its embryonic development mechanism remains unclear. We investigated the flower bud differentiation, megaspore and microspore formation, gametophyte development, and embryo and endosperm development in L. davurica. Our aim was to elucidate the relationship between the external morphology and internal development processes of male and female floral organs during growth, as well as the reproductive factors influencing fruiting. The results indicated that although the pistil develops later than the stamen during flower bud differentiation, both organs mature synchronously before flowering. L. davurica pollen exhibits three germination grooves, a reticulate outer wall, and papillary structures on the anther surface. In vivo pollination experiments revealed abnormal spiral growth of L. davurica pollen tubes within the style and the occurrence of callus plugs, which may reduce the seed setting rate. The anther wall development follows the dicotyledonous type, with tetrads formed through microspore meiosis exhibiting both left–right symmetry and tetrahedral arrangements. L. davurica has a single ovule, and the embryo sac develops in the monosporic polygonum type. After dormancy, the zygote undergoes multiple divisions, progressing through spherical, heart-shaped, and torpedo-shaped embryo stages, culminating in a mature embryo. A mature seed comprises cotyledons, hypocotyl, embryo, radicle, and seed coat. Phylogenetic tree analysis reveals a close genetic relationship between L. davurica and other leguminous plants from the genera Lespedeza and Medicago. This study provides valuable insights into the regulation of flowering and hybrid breeding in leguminous plants and offers a new perspective on the development of floral organs and seed setting rates. [ABSTRACT FROM AUTHOR]

The continuously refined genome assembly of the Chinese cabbage accession Chiifu is widely recognized as the reference for Brassica rapa. However, the high self-incompatibility of Chiifu limits its broader utilization. In this study, we report the development of self-compatible Chiifu lines through a meticulous markerassisted selection (MAS) strategy, involving the substitution of the Chiifu allele of MLPK (M-locus protein kinase) with that from the self-compatible Yellow Sarson (YS). A YS-based marker (SC-MLPK) was employed to screen 841 B. rapa accessions, confirming that all eight accessions with the mlpk/mlpk (mm) genotype exhibited self-compatibility. Additionally, we designed 131 High-Resolution Melting (HRM) markers evenly distributed across the B. rapa genome as genomic background selection (GBS) markers to facilitate the introgression of self-compatibility from YS into Chiifu along with SC-MLPK. Genome background screening revealed that the BC3S1 population had a proportion of the recurrent parent genome (PR) ranging from 93.9% to 98.5%. From this population, we identified self-compatible individuals exhibiting a high number of pollen tubes penetrating stigmas (NPT) (>25) and a maximum compatibility index (CI) value of 7.5. Furthermore, we selected two individuals demonstrating significant similarity to Chiifu in both genetic background and morphological appearance, alongside self-compatibility. These selected individuals were self-pollinated to generate two novel lines designated as SCChiifu Lines. The development of these self-compatible Chiifu lines, together with the SC-MLPK marker and the set of HRM markers, represents valuable tools for B. rapa genetics and breeding. [ABSTRACT FROM AUTHOR]

In the pistil of flowering plants, each ovule usually associates with a single pollen tube for fertilization. This one-to-one pollen tube guidance, which contributes to polyspermy blocking and efficient seed production, is largely different from animal chemotaxis of many sperms to one egg. However, the functional mechanisms underlying the directional cues and polytubey blocks in the depths of the pistil remain unknown. Here, we develop a two-photon live imaging method to directly observe pollen tube guidance in the pistil of Arabidopsis thaliana, clarifying signaling and cellular behaviors in the one-to-one guidance. Ovules are suggested to emit multiple signals for pollen tubes, including an integument-dependent directional signal that reaches the inner surface of the septum and adhesion signals for emerged pollen tubes on the septum. Not only FERONIA in the septum but ovular gametophytic FERONIA and LORELEI, as well as FERONIA- and LORELEI-independent repulsion signal, are involved in polytubey blocks on the ovular funiculus. However, these funicular blocks are not strictly maintained in the first 45 min, explaining previous reports of polyspermy in flowering plants. Synopsis: Two-photon imaging reveals the spatiotemporal regulation of pollen tube guidance based on multistep blocking systems to prevent polyspermy. Development of a two-photon live imaging method for direct observation of pollen tube guidance. Outer integument dependent long-range directional signal acts as pollen tube adhesion and emergence signal. FERONIA and LORELEI-dependent/-independent polytubey blocks on the funiculus are not strictly maintained during the first 45 min. Two-photon imaging reveals the spatiotemporal regulation of pollen tube guidance based on multistep blocking systems to prevent polyspermy. [ABSTRACT FROM AUTHOR]

Most Aristolochiaceae species studied so far are from temperate regions, bearing self‐compatible protogynous trap flowers. Although self‐incompatibility has been suggested for tropical species, the causes of self‐sterility in this family remain unknown. To fill this gap, we studied the pollination of the tropical Aristolochia esperanzae, including the physical and physiological anti‐selfing mechanisms.Floral visitors trapped inside flowers were collected to determine the pollinators. Protogyny was characterized by observing the temporal expression of sexual phases and stigmatic receptivity tests. The breeding system was investigated using hand‐pollination treatments. Pollen tube growth was observed using epifluorescence to identify the self‐incompatibility mechanism.Flies were the most frequent visitors found inside A. esperanzae trap flowers, with individuals from the family Ulidiidae being potential pollinators since they carried pollen. The characteristic flower odour and presence of larvae indicate that A. esperanzae deceives flies through oviposition‐site mimicry. Although this species showed incomplete protogyny, stigmatic receptivity decreased during the male phase, avoiding self‐pollination. Fruits developed only after cross‐ and open pollination, indicating that the population is non‐autonomous, non‐apomictic, and self‐sterile. This occurred through a delay in the growth of geitonogamous pollen tubes to the ovary and lower ovule penetration, indicating a late‐acting self‐incompatibility mechanism.Our findings expand the number of families in which late‐acting self‐incompatibility has been reported, demonstrating that it is more widespread than previously thought, especially when considering less‐studied tropical species among the basal angiosperms. [ABSTRACT FROM AUTHOR]

The honeybee, Apis mellifera, stands out for its positive image due to its contribution to crop pollination and honey production, which facilitated its widespread distribution. However, large apiaries resulting in high honeybee densities could increase pollination frequency while increasing competition for floral resources, ultimately affecting native plant fitness.We studied the impact of managed honeybee hives on pollination and reproductive success of native plants in Villavicencio Nature Reserve, Mendoza, Argentina. During the flowering peak, we studied pollination and reproduction of three native plant species (Larrea divaricata, L. cuneifolia and Zuccagnia punctata) near and far from the hives. We estimated pollen deposition on flower stigmas, pollen tubes developed in flower pistils, fruit set, seed set and seed viability.We found that the honeybee hives had a positive effect on the reproduction of the self‐compatible species, L. divaricata. For the self‐incompatible species, results differed among species: Hives had positive effects on the pollination and negative effects on the reproduction of L. cuneifolia, while they had negative effects on the reproduction of Z. punctata.Synthesis and applications. Beekeeping is increasingly turning to natural areas in search of better quality honey; however, increased honeybee abundance in the field could influence the reproduction of native plants. Our results show that the introduction of managed hives negatively affected the reproduction of self‐incompatible native plants. This result allows us to make several recommendations for conservation and management actions concerning beekeeping in natural areas, regarding the among‐year rotation of the location of hives, the number of hives per site, and the need to monitor the reproduction of self‐incompatible species. [ABSTRACT FROM AUTHOR]

SUMMARY: Capturing images of the nuclear dynamics within live cells is an essential technique for comprehending the intricate biological processes inherent to plant cell nuclei. While various methods exist for imaging nuclei, including combining fluorescent proteins and dyes with microscopy, there is a dearth of commercially available dyes for live‐cell imaging. In Arabidopsis thaliana, we discovered that nuclei emit autofluorescence in the near‐infrared (NIR) range of the spectrum and devised a non‐invasive technique for the visualization of live cell nuclei using this inherent NIR autofluorescence. Our studies demonstrated the capability of the NIR imaging technique to visualize the dynamic behavior of nuclei within primary roots, root hairs, and pollen tubes, which are tissues that harbor a limited number of other organelles displaying autofluorescence. We further demonstrated the applicability of NIR autofluorescence imaging in various other tissues by incorporating fluorescence lifetime imaging techniques. Nuclear autofluorescence was also detected across a wide range of plant species, enabling analyses without the need for transformation. The nuclear autofluorescence in the NIR wavelength range was not observed in animal or yeast cells. Genetic analysis revealed that this autofluorescence was caused by the phytochrome protein. Our studies demonstrated that nuclear autofluorescence imaging can be effectively employed not only in model plants but also for studying nuclei in non‐model plant species. [ABSTRACT FROM AUTHOR]

An initial cross of V. darrowii 'Johnblue' (Darrow's blueberry) × V. vitis-idaea 'Red Sunset' (lingonberry) produced more than 30 true intersectional diploid hybrids as confirmed by molecular markers. The most vigorous of these hybrids was extensively evaluated. This hybrid, US 2535-A, was floriferous and morphologically intermediate to the respective parents. Examination of pollen suggested low male fertility. Numerous crosses using the hybrid as a female reflected similarly low fertility and potential crossing barriers. Stylar examination suggested blockage of pollen tube growth in self-pollinations and significantly retarded growth in backcross pollinations. Nonetheless, two confirmed hybrid offspring were produced using the F1 hybrid as a female in crosses with V. vitis-idaea and V. darrowii, respectively. In a second set of crosses utilizing additional V. darrowii and V. vitis-idaea genotypes, another 23 verified hybrids in seven parental combinations were produced. Hybrids such as the ones presented offer the potential for generating de novo interspecific fruit types in blueberry and/or broadening the adaptation of lingonberry. [ABSTRACT FROM AUTHOR]

The actin (ACT) family genes are essential for plant growth and development. However, the evolution and function of the ACT family within the Rosaceae species, particularly in pear, remain poorly understood. Here, we identified 41 ACT genes across five Rosaceae species based on phylogenetic and structural features that can be categorized into two primary groups: subfamily I (reproductive) and II (vegetative). Evolutionary analysis suggests that purifying selection played a crucial role in the evolution of the ACT family in Rosaceae, and whole genome duplication (WGD) and dispersed duplication led to the expansion of ACT genes. The pear genome contains twelve ACT genes, which can be classified into two groups based on their phylogeny and expression patterns: reproductive (PbrACT1-5) and vegetative (PbrACT6-12), further validating the reliability of the ACT family classification in Rosaceae. Expression analysis of twelve PbrACT genes across various pear tissues indicated that five genes from subfamily I (PbrACT1-5) were predominantly expressed in pollen tubes, with PbrACT1 exhibiting the highest level of expression. Knockdown of PbrACT1 expression in pear pollen tubes significantly diminished F-actin levels, triggered F-actin depolymerization, and resulted in pollen tube growth inhibition, indicating that PbrACT1 is essential for the formation of the microfilament skeleton during pear pollen tube growth. Overall, this study offers significant insights into the evolution and function of ACT genes in Rosaceae and enhances our understanding of PbrACT in microfilament formation in pear pollen tubes. [ABSTRACT FROM AUTHOR]

Rice straw lignin was extracted via alkaline hydrolysis and structurally characterized using FT-IR and 1H NMR spectra. Ethyl acetate extract of acid solubilized lignin was found to contain p-coumaric acid, ferulic acid and caffeic acid as major phenolic acids which were isolated and characterized using spectral data. Amides of isolated phenolic acids were synthesized by their reaction with propyl and butyl amines using microwave irradiation and analysed using spectral studies. Phenolic acids and amides were evaluated for their effect on pollen germination and tube growth in pumpkin. Pollen tube length was significantly increased with N-butyl-3-(3, 4-dihydroxyphenyl) acrylamide and N-butyl-3-(4-hydroxyphenyl) acrylamide at 5 ppm concentration than the control. These results could be utilised in increasing pollen tube length of Cucurbita pepo while making interspecific cross between C. moschata and C. pepo in order to transfer hull-less character of C. pepo to virus resistant C. moschata genotypes. [ABSTRACT FROM AUTHOR]

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

Pollen tube tip growth requires intricate Ca2+ signaling. Recent studies have also identified rapid alkalization factor (RALF)-family peptides and their receptors as critical components for pollen tube tip growth and integrity. The functional relationship of RALF and calcium signaling modules remains largely unclear. Here we report that disruption of RALF signaling pathway abolished the cytosolic Ca2+ gradient in the pollen tube, indicating that Ca2+ signaling is downstream of the RALF signaling pathway. We identified MILDEW RESISTANCE LOCUS O (MLO) family proteins MLO1, 5, 9, 15, as Ca2+ channels required for Ca2+ influx and pollen tube integrity. We further reconstituted the biochemical pathway in which signaling via RALF and RALF receptors activated MLO1/5/9/15 calcium channels. Together, we conclude that RALF peptides derived from pollen tube bind to their receptors to establish pollen tube Ca2+ gradient through activation of the MLO channels. Our finding has thus provided a mechanistic link between the RALF signaling pathway and Ca2+ signaling in controlling pollen tube integrity and growth.

In higher plants, mature male gametophytes have distinct apertures. After pollination, pollen grains germinate, and a pollen tube grows from the aperture to deliver sperm cells to the embryo sac, completing fertilization. In rice, the pollen aperture has a single-pore structure with a collar-like annulus and a plug-like operculum. A crucial step in aperture development is the formation of aperture plasma membrane protrusion (APMP) at the distal polar region of the microspore during the late tetrad stage. Previous studies identified OsINP1 and OsDAF1 as essential regulators of APMP and pollen aperture formation in rice, but their precise molecular mechanisms remain unclear. We demonstrate that the Poaceae-specific OsSRF8 gene, encoding a STRUBBELIG-receptor family 8 protein, is essential for pollen aperture formation in Oryza sativa. Mutants lacking functional OsSRF8 exhibit defects in APMP and pollen aperture formation, like loss-of-function OsINP1 mutants. OsSRF8 is specifically expressed during early anther development and initially diffusely distributed in the microsporocytes. At the tetrad stage, OsSRF8 is recruited by OsINP1 to the pre-aperture region through direct protein-protein interaction, promoting APMP formation. The OsSRF8-OsINP1 complex then recruits OsDAF1 to the APMP site to co-regulate annulus formation. Our findings provide insights into the mechanisms controlling pollen aperture formation in cereal species. At the tetrad stage, OsSRF8 interacts with OsINP1 to promote the formation of aperture plasma membrane protrusion (APMP). Then, the OsINP1-OsSRF8 protein complex recruits OsDAF1 to the APMP site and co-regulate pollen aperture formation in rice. [ABSTRACT FROM AUTHOR]

Pollen, the male gametophyte of seed plants, is extremely sensitive to UV light, which may prevent fertilization. As a result, strategies to improve plant resistance to solar ultraviolet (UV) radiation are required. The tardigrade damage suppressor protein (Dsup) is a putative DNA-binding protein that enables tardigrades to tolerate harsh environmental conditions, including UV radiation, and was therefore considered as a candidate for reducing the effects of UV exposure on pollen. Tobacco pollen was genetically engineered to express Dsup and then exposed to UV-B radiation to determine the effectiveness of the protein in increasing pollen resistance. To establish the preventive role of Dsup against UV-B stress, we carried out extensive investigations into pollen viability, germination rate, pollen tube length, male germ unit position, callose plug development, marker protein content, and antioxidant capacity. The results indicated that UV-B stress has a significant negative impact on both pollen grain and pollen tube growth. However, Dsup expression increased the antioxidant levels and reversed some of the UV-B-induced changes to pollen, restoring the proper distance between the tip and the last callose plug formed, as well as pollen tube length, tubulin, and HSP70 levels. Therefore, the expression of heterologous Dsup in pollen may provide the plant male gametophyte with enhanced responses to UV-B stress and protection against harmful environmental radiation. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) can serve as signaling molecules that are essential for plant growth and development but abiotic stress can lead to ROS increases to supraoptimal levels resulting in cellular damage. To ensure efficient ROS signaling, cells have machinery to locally synthesize ROS to initiate cellular responses and to scavenge ROS to prevent it from reaching damaging levels. This review summarizes experimental evidence revealing the role of ROS during multiple stages of plant reproduction. Localized ROS synthesis controls the formation of pollen grains, pollen−stigma interactions, pollen tube growth, ovule development, and fertilization. Plants utilize ROS‐producing enzymes such as respiratory burst oxidase homologs and organelle metabolic pathways to generate ROS, while the presence of scavenging mechanisms, including synthesis of antioxidant proteins and small molecules, serves to prevent its escalation to harmful levels. In this review, we summarized the function of ROS and its synthesis and scavenging mechanisms in all reproductive stages from gametophyte development until completion of fertilization. Additionally, we further address the impact of elevated temperatures induced ROS on impairing these reproductive processes and of flavonol antioxidants in maintaining ROS homeostasis to minimize temperature stress to combat the impact of global climate change on agriculture. Summary statement: This review examines the role of reactive oxygen species (ROS) in the regulation of plant reproduction, summarizing the positive roles of localized ROS synthesis at multiple developmental stages of plant reproduction and the negative effects of stress‐induced ROS on reproductive fitness. [ABSTRACT FROM AUTHOR]

Self‐incompatibility (SI) is an intraspecific reproductive barrier widely present in angiosperms. The SI system with the broadest occurrence in angiosperms is based on an S‐RNase linked to a cluster of multiple S‐locus F‐box (SLF) genes found in the Solanaceae, Plantaginaceae, Rosaceae, and Rutaceae. Recent studies reveal that non‐self S‐RNase is degraded by the Skip Cullin F‐box (SCF)SLF‐mediated ubiquitin–proteasome system in a collaborative manner in Petunia, but how self‐RNase functions largely remains mysterious. Here, we show that S‐RNases form S‐RNase condensates (SRCs) in the self‐pollen tube cytoplasm through phase separation and the disruption of SRC formation breaks SI in self‐incompatible Petunia hybrida. We further find that the pistil SI factors of a small asparagine‐rich protein HT‐B and thioredoxin h together with a reduced state of the pollen tube all promote the expansion of SRCs, which then sequester several actin‐binding proteins, including the actin polymerization factor PhABRACL, the actin polymerization activity of which is reduced by S‐RNase in vitro. Meanwhile, we find that S‐RNase variants lacking condensation ability fail to recruit PhABRACL and are unable to induce actin foci formation required for pollen tube growth inhibition. Taken together, our results demonstrate that phase separation of S‐RNase promotes SI response in P. hybrida, revealing a new mode of S‐RNase action. [ABSTRACT FROM AUTHOR]

Autocrine signaling pathways regulated by RAPID ALKALINIZATION FACTORs (RALFs) control cell wall integrity during pollen tube germination and growth in Arabidopsis (Arabidopsis thaliana). To investigate the role of pollen-specific RALFs in another plant species, we combined gene expression data with phylogenetic and biochemical studies to identify candidate orthologs in maize (Zea mays). We show that Clade IB ZmRALF2/3 mutations, but not Clade III ZmRALF1/5 mutations, cause cell wall instability in the sub-apical region of the growing pollen tube. ZmRALF2/3 are mainly located in the cell wall and are partially able to complement the pollen germination defect of their Arabidopsis orthologs AtRALF4/19. Mutations in ZmRALF2/3 compromise pectin distribution patterns leading to altered cell wall organization and thickness culminating in pollen tube burst. Clade IB, but not Clade III ZmRALFs, strongly interact as ligands with the pollen-specific Catharanthus roseus RLK1-like (CrRLK1L) receptor kinases Z. mays FERONIA-like (ZmFERL) 4/7/9, LORELEI-like glycosylphosphatidylinositol-anchor (LLG) proteins Z. mays LLG 1 and 2 (ZmLLG1/2), and Z. mays pollen extension-like (PEX) cell wall proteins ZmPEX2/4. Notably, ZmFERL4 outcompetes ZmLLG2 and ZmPEX2 outcompetes ZmFERL4 for ZmRALF2 binding. Based on these data, we suggest that Clade IB RALFs act in a dual role as cell wall components and extracellular sensors to regulate cell wall integrity and thickness during pollen tube growth in maize and probably other plants. Pollen-specific RAPID ALKALINIZATION FACTORs interact with receptor kinases, GPI-anchored proteins, and cell wall proteins to regulate cell wall integrity during pollen tube growth in maize. [ABSTRACT FROM AUTHOR]

This article, titled "Letter to the Editor: Blue Light Irradiation Induces Pollen Tube Rupture in Various Flowering Plants," discusses the phenomenon of pollen tube (PT) rupture in flowering plants when exposed to blue light (BL) irradiation. The study found that PTs in Arabidopsis, torenia, and tobacco experienced PT rupture and an influx of calcium ions after BL irradiation. The researchers also observed that PT rupture frequency increased with the intensity of the BL irradiation. The study suggests that BL-induced PT rupture and calcium influx could be a novel method to control PT bursts and offers insights into the interplay between PT integrity and calcium influx. [Extracted from the article]

The genus Dyckia (Bromeliaceae) is endemic to South America, and its species show important ecological roles in xeric environments. The flowering phenology as well as floral and reproductive biology were monitored monthly in Dyckia dissitiflora at two sites (Bela Vista: 11°42′03.4″ S 39°05′21.7″ W and Barra do Vento: 11°37′58.1″ S 39°03′33.7″ W) in the municipality of Serrinha, Bahia, Brazil. Flowering occurs in the early austral summer with a peculiar time of beginning of anthesis (10:00–11:00), offering resources 18 h after the first petal movements. Pollen viability was 98%, with a high production of pollen grains. Stigma receptivity is continuous from flower opening to senescence, and nectar production initiates at 04:00 and extends until 18:00. The species is self‐compatible and autogamous, but not agamospermic. Pollen tubes developed and reached the micropyle within 24 h in all of the reproductive tests. The hummingbird Chlorostilbon lucidus was the only floral visitor and pollinator (frequency = 0.82 ± 0.02). Fruiting occurs 3 days after anthesis, and the seeds are wind‐dispersed. Self‐compatibility and autogamy are essential strategies for the reproductive success of D. dissitiflora in light of the low number and visit frequency of its pollinators, and it is favored by slow floral movements and the position of the stigmas in relation to stamens. [ABSTRACT FROM AUTHOR]

The S-RNase gene plays an essential role in the gametophytic self-incompatibility (GSI) system of Pyrus. It codes for the stylar-expressed S-RNase protein which inhibits the growth of incompatible pollen tubes through cytotoxicity and the induction of programmed cell death in the pollen tube. While research on the Pyrus GSI system has primarily focused on the S-RNase gene, there is still a lack of insight into its spatiotemporal expression profile and the factors that regulate it. Previous studies have suggested that S-RNase expression in the style is influenced by pollination and is dependent on the compatibility type. We here continue on this basic hypothesis by analyzing the spatiotemporal expression of the S-RNase alleles in Pyrus communis "Conference" styles in response to different types of pollination; namely, upon full- and semi-compatible pollination and upon incompatible selfing. The results revealed that temporal dynamics of S-RNase expression are influenced by the pollen's compatibility type, indicating the presence of a signaling mechanism between pollen and style to control S-RNase production during pollen tube growth. In our experiment, S-RNase expression continuously decreased after cross-pollination and in the unpollinated control. However, after a fully incompatible pollination, S-RNase expression remained constant. Finally, semi-compatible pollination showed a initially constant S-RNase expression for both alleles followed by a strong decrease in expression. Based on these results and previous findings, we propose a regulatory mechanism to explain the effect of pollination and the associated compatibility type on S-RNase expression in the style. This proposed mechanism could be used as a starting point for future research. [ABSTRACT FROM AUTHOR]

The morphological structure of flowers of Lonicera L. species, the study of their biology, and observations show that the studied species are mainly cross-pollinated plants. Bees, ants, and other insects visit flowers for nectar, and thus they are considered one of the main pollinators of the plant. Pollen viability is an important indicator in the study of the generative development of plants. Pollen viability can be objectively evaluated using the method of germination in an artificial food medium. There is little literature data on pollen germination of Lonicera L. species, based on which, the fertility and sterility of pollen, and the effect of concentrations of different substances on pollen germination were studied. [ABSTRACT FROM AUTHOR]

Double fertilization in many flowering plants (angiosperms) often occurs during the hot summer season, but the mechanisms that enable angiosperms to adapt specifically to high temperatures are largely unknown. The actin cytoskeleton is essential for pollen germination and the polarized growth of pollen tubes, yet how this process responds to high temperatures remains unclear. Here, we reveal that the high thermal stability of 11 Arabidopsis (Arabidopsis thaliana) actin-depolymerizing factors (ADFs) is significantly different: ADFs that specifically accumulate in tip-growing cells (pollen and root hairs) exhibit high thermal stability. Through ancestral protein reconstruction, we found that subclass II ADFs (expressed specifically in pollen) have undergone a dynamic wave-like evolution of the retention, loss, and regeneration of thermostable sites. Additionally, the sites of AtADF7 with high thermal stability are conserved in ADFs specific to angiosperm pollen. Moreover, the high thermal stability of ADFs is required to regulate actin dynamics and turnover at high temperatures to promote pollen germination. Collectively, these findings suggest strategies for the adaptation of sexual reproduction to high temperature in angiosperms at the cell biology level. Actin-depolymerizing factors in angiosperm pollen have evolved high thermostability, which involves regulating actin dynamics to promote pollen germination at high temperature. [ABSTRACT FROM AUTHOR]

Putrescine, spermine, and spermidine are among the most significant polyamines for plant growth and development, including pollen tube elongation. Although the effects of putrescine and spermine are well-known on tube elongation, little is known about the impact of spermidine. The aim of this study is to reveal how exogenic spermidine impinges positively and negatively on the factors involved in tube elongation such as actin cytoskeleton organization, calcium, pH and reactive oxygen species gradients, sucrose synthase enzyme activity, distribution of cell wall polysaccharide, tube nuclei movement. Treatment of 0.01 mM spermidine which showed a positive effect, increased actin dynamism, and, caused a decrease in the amount of cellulose in the tube apex by coordinating the sucrose synthase enzyme localization. These changes were reflected in the tube elongation velocities and oscillations as an increase, allowing the tubes to elongate faster. Treatment of 0.5 mM spermidine which showed a negative effect, caused changes in intracellular calcium, pH and reactive oxygen species gradients and these alterations reduced the dynamism of actin filaments. Decreased actin dynamism affected the localization of the sucrose synthase enzyme, inhibited the transport of newly synthesized wall materials to the tube apex and the transport of the generative nucleus to the tube apex. These changes were reflected in the tube elongation velocities and oscillations as a decrease, allowing the tubes to elongate slower. Results could be contributed to the explanation of the effect of spermidine in plant growth and development, including pollen tube elongation. [ABSTRACT FROM AUTHOR]

One of the most vulnerable phases in the plant life cycle is sexual reproduction, which depends on effective pollen transfer, but also on the thermotolerance of pollen grains. Pollen thermotolerance is temperature-dependent and may be reduced by increasing temperature associated with global warming. A growing body of research has focused on the effect of increased temperature on pollen thermotolerance in crops to understand the possible impact of temperature extremes on yield. Yet, little is known about the effects of temperature on pollen thermotolerance of wild plant species. To fill this gap, we selected Lotus corniculatus s.l. (Fabaceae), a species common to many European habitats and conducted laboratory experiments to test its pollen thermotolerance in response to artificial increase in temperature. To test for possible local adaptation of pollen thermal tolerance, we compared data from six lowland (389=451 m a.s.l.) and six highland (841=1,030 m a.s.l.) populations. We observed pollen germination in vitro at 15 °C, 25 °C, 30 °C, and 40 °C. While lowland plants maintained a stable germination percentage across a broad temperature range (15=30 °C) and exhibited reduced germination only at extremely high temperatures (40 °C), highland plants experienced reduced germination even at 30 °C=temperatures commonly exceeded in lowlands during warm summers. This suggests that lowland populations of L. corniculatus may be locally adapted to higher temperature for pollen germination. On the other hand, pollen tube length decreased with increasing temperature in a similar way in lowland and highland plants. The overall average pollen germination percentage significantly differed between lowland and highland populations, with highland populations displaying higher germination percentage. On the other hand, the average pollen tube length was slightly smaller in highland populations. In conclusion, we found that pollen thermotolerance of L. corniculatus is reduced at high temperature and that the germination of pollen from plant populations growing at higher elevations is more sensitive to increased temperature, which suggests possible local adaptation of pollen thermotolerance. [ABSTRACT FROM AUTHOR]

MYB98 is master regulator of the molecular network involved in pollen tube attraction. Until recently, it was unclear how this gene exhibits exclusively synergid cell-specific expression in ovule. Our recent study has established that a 16-bp-long SaeM element is crucial for its synergid cell-specific expression in ovule, and an 84-bp-long fragment harboring SaeM is sufficient to drive the process. In this study, we have developed a workflow to predict functional roles of potential transcription factors (TFs) putatively binding to the promoter region, taking MYB98 promoter as a test subject. After sequential assessment of co-expression pattern, network analysis, and potential master regulator identification, we have proposed a multi-TF model for MYB98 regulation. Our study suggests that ANL2, GT-1, and their respective homologs could be direct regulators of MYB98 and indicates that TCP15, TCP16, FRS9, and HB34 are likely master regulators of the majority of the TFs involved in its regulation. Comprehensive studies in the future are expected to offer more insights into such propositions. Developed workflow can be used while designing similar regulome-related studies for any other species and genes. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) is an important forage crop worldwide, but molecular genetics and breeding research in this species are hindered by its self-incompatibility (SI). Although the mechanisms underlying SI have been extensively studied in other plant families, SI in legumes, including alfalfa, remains poorly understood. Here, we determined that self-pollinated pollen tubes could germinate on the stigma of alfalfa, grow through the style, and reach the ovarian cavity, but the ovules collapsed ~48 h after self-pollination. A transcriptomic analysis of dissected pistils 24 h after self-pollination identified 941 differently expressed genes (DEGs), including 784 upregulated and 157 downregulated genes. A gene ontology (GO) analysis showed that the DEGs were highly enriched in functions associated with the regulation of pollen tube growth and pollen germination. A Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that pentose and glucuronate interconversion, plant hormone signal transduction, the spliceosome, and ribosomes might play important roles in SI. Our co-expression analysis showed that F-box proteins, serine/threonine protein kinases, calcium-dependent protein kinases (CDPKs), bHLHs, bZIPs, and MYB-related family proteins were likely involved in the SI response. Our study provides a catalog of candidate genes for further study to understand SI in alfalfa and related legumes. [ABSTRACT FROM AUTHOR]

The involvement of Ca2+ ions in angiosperms sexual processes is well established, while in gymnosperms, such knowledge remains limited and is still a topic of discussion. In this study, we focused on Larix decidua, using Alizarin-red S staining and the pyroantimonate method to examine the tissue and subcellular distribution of free and loosely bound Ca2+ ions at different stages of the male gametophyte's development and its interaction with the ovule. Our findings show that in larch, both the germination of pollen grains and the growth of pollen tubes occur in an environment rich in Ca2+. These ions play a crucial role in the adhesion of the pollen grain to the stigmatic tip and its subsequent movement to the micropylar canal. There is a significant presence of free and loosely bound Ca2+ ions in both the fluid of the micropylar canal and the extracellular matrix of the nucellus. As the pollen tube extends through the nucellus, we observed a notable accumulation of Ca2+ ions just above the entry to the mature archegonium, a region likely crucial for the male gametophyte's directional growth. Meanwhile, the localized presence of free and loosely bound Ca2+ ions within the egg cell cytoplasm may inhibit the pollen tubes growth and rupture, playing an important role in fertilization. [ABSTRACT FROM AUTHOR]

Premise of research. Hermaphroditic flowering plants achieve reproductive success via both seed siring (male function) and seed production (female function). In pollinator-dependent plants, both gender functions depend on successful pollination, in which pollen is transferred from anthers to stigmas, resulting in seed production. However, it is still unclear how male (pollen removal) and female (pollen receipt and pollen tubes) components of pollination success are associated with each other and which community-level processes drive each function in coflowering communities. Methodology. In a pollen-limited environment with low pollinator visitation rates and most ovules left unfertilized, we measured pollen removal, pollen receipt, and pollen tubes across 41 species and tested their correlation and how floral density and reproductive traits predict each component. Pivotal results. One-quarter of the pollen remained on flowers on average, while disproportionate increases in pollen removal were often associated with small increases in pollen receipt and pollen tubes. Abundant plants suffered intraspecific competition, while interspecific individuals engaged in facilitative interactions via all components (pollen removal, pollen receipt, and pollen tubes) but in varying strengths. Plants with small display size and flowering synchronously with the plant community were at a disadvantage in terms of pollen removal but at an advantage in terms of pollen receipt and pollen tubes. Conclusions. The natural low pollinator availability may limit both gender functions, leading to the correlation between pollination success components. Nevertheless, opposing community-level processes drive each pollination success component in plants with small display size. Our results suggest that coflowering context is important to understand potential synergies and conflicts between gender functions at the pollinator attraction stage, which are common evolutionary consequences of bisexuality. [ABSTRACT FROM AUTHOR]

Key message: Pollen tubes from closely related species and mutants lacking pollen tube MYB transcription factors are able to initiate FER/LRE-dependent synergid cell calcium oscillations. Reproductive isolation leads to the evolution of new species; however, the molecular mechanisms that maintain reproductive barriers between sympatric species are not well defined. In flowering plants, sperm cells are immotile and are delivered to female gametes by the pollen grain. After landing on the stigmatic surface, the pollen grain germinates a polarized extension, the pollen tube, into floral tissue. After growing via polar extension to the female gametes and shuttling its cargo of sperm cells through its cytoplasm, the pollen tube signals its arrival and identity to synergid cells that flank the egg. If signaling is successful, the pollen tube and receptive synergid cell burst, and sperm cells are released for fusion with female gametes. To better understand cell–cell recognition during reproduction and how reproductive barriers are maintained between closely related species, pollen tube-initiated synergid cell calcium ion dynamics were examined during interspecific crosses. It was observed that interspecific pollen tubes successfully trigger synergid cell calcium oscillations—a hallmark of reproductive success—but signaling fails downstream of key signaling genes and sperm are not released. This work further defines pollen tube–synergid cell signaling as a critical block to interspecific hybridization and suggests that the FERONIA/LORELEI signaling mechanism plays multiple parallel roles during pollen tube reception. [ABSTRACT FROM AUTHOR]

Key message: In Araucaria angustifolia, the seed scale is part of the ovule, the female gametophyte presents a monosporic origin and arises from a coenocytic tetrad, and the pollen tube presents a single axis. The seed cone of conifers has many informative features, and its ontogenetic data may help interpret relationships among function, development patterns, and homology among seed plants. We reported the seed cone development, from pollination to pre-fertilization, including seed scale, ovule ontogeny, and pollen tube growth in Araucaria angustifolia. The study was performed using light microscopy, scanning electron microscopy, and X-ray microcomputed tomography (μCT). During the pollination period, the ovule arises right after the seed scale has emerged. From that event to the pre-fertilization period takes about 14 months. Megasporogenesis occurs three weeks after ovule formation, producing a coenocytic tetrad. At the same time as the female gametophyte's first nuclear division begins, the pollen tube grows through the seed scale adaxial face. Until maturity, the megagametophyte goes through the free nuclei stage, cellularization stage, and cellular growth stage. Along its development, many pollen tubes develop in the nucellar tissue extending straight toward the female gametophyte. Our observations show that the seed scale came out of the same primordia of the ovule, agreeing with past studies that this structure is part of the ovule itself. The formation of a female gametophyte with a monosporic origin that arises from a coenocytic tetrad was described for the first time in conifers, and the three-dimensional reconstruction of the ovule revealed the presence of pollen tubes with only one axis and no branches, highlighting a new pattern of pollen tube growth in Araucariaceae. [ABSTRACT FROM AUTHOR]

Cold shock domain proteins (CSPs), initially identified in Escherichia coli, have been demonstrated to play a positive role in cold resistance. Previous studies in wheat, rice, and Arabidopsis have indicated the functional conservation of CSPs in cold resistance between bacteria and higher plants. However, the biological functions of PbrCSPs in pear pollen tubes, which represent the fragile reproductive organs highly sensitive to low temperature, remain largely unknown. In this study, a total of 22 CSPs were identified in the seven Rosaceae species, with a focus on characterizing four PbrCSPs in pear (Pyrus bretschneideri Rehder). All four PbrCSPs were structurally conserved and responsive to the abiotic stresses, such as cold, high osmotic, and abscisic acid (ABA) treatments. PbrCSP1, which is specifically expressed in pear pollen tubes, was selected for further research. PbrCSP1 was localized in both the cytoplasm and nucleus. Suppressing the expression of PbrCSP1 significantly inhibited the pollen tube growth in vitro. Conversely, overexpression of PbrCSP1 promoted the growth of pear pollen tubes under the normal condition and, notably, under the cold environment at 4 °C. These findings highlight an essential role of PbrCSP1 in facilitating the normal growth and enhancing cold resistance in pear pollen tubes. [ABSTRACT FROM AUTHOR]

Gametophytic self-incompatibility (GSI) has been mainly described in species-rich clades within Orchidaceae. We report GSI for a genus within Maxillariinae, one of the most conspicuous and diverse subtribes of neotropical orchids. Here, we describe the reproductive system of Brasiliorchis picta, B. phoenicanthera, and B. porphyrostele. Anatomical studies of fruit development showed that pollen tubes of aborted, self-pollinated flowers degenerate half-way in the stylar channel and never reach the ovules. Spontaneous self-pollination and emasculation set no fruits for none of the sampled species, thus supporting the hypothesis that these three species studied rely on the agency of pollinators and pollinator-mediated cross-pollination to set fruit. Fruit set from cross-pollinations ranged from 33.4 to 77.5%. One self-pollinated fruit of B. porphyrostele developed to completion. All other fruits aborted between 10 and 21 days after pollination. These data support previous evidence of variable strength GSI being exhibited in orchid species. Additional studies of self-incompatibility systems are needed to evaluate their role in species diversification and evolution of reproductive strategies in Maxillariinae and to allow for effective conservation strategies of threatened orchid species. [ABSTRACT FROM AUTHOR]

Understanding plant reproduction offers potential routes both to impact on seed crop agriculture and to reveal key principles of plant cell signalling. Cell–cell signalling during plant reproduction revolves around the interactions between a small family of receptor-like kinases, their coreceptors, and ligands. Several specific peptides and carbohydrates have recently been confirmed as ligands in reproductive signalling, opening new avenues to investigate their interactions and potentially distinct downstream effects. Known downstream signalling responses include the production of reactive oxygen species, the generation of specific calcium signatures, and changes to the cell wall. Plant reproduction is a complex, highly-coordinated process in which a single, male germ cell grows through the maternal reproductive tissues to reach and fertilise the egg cell. Focussing on Arabidopsis thaliana , we review signalling between male and female partners which is important throughout the pollen tube journey, especially during pollen tube reception at the ovule. Numerous receptor kinases and their coreceptors are implicated in signal perception in both the pollen tube and synergid cells at the ovule entrance, and several specific peptide and carbohydrate ligands for these receptors have recently been identified. Clarifying the interplay between these signals and the downstream responses they instigate presents a challenge for future research and may help to illuminate broader principles of plant cell–cell communication. [ABSTRACT FROM AUTHOR]

Berry fruits produced by Vaccinium (Ericaceae) plants are small but have a signature flavor and have become increasingly popular in the 21st century. However, self-incompatibility (SI) results in a relatively low fruit-set ratio and reduced fruit quality in Vaccinium. In this study, using Vaccinium ashei (V. ashei) styles after cross-pollination (CP) and self-pollination (SP) as material, transcriptomics and gene expression analyses were performed using high-throughput RNA sequencing and quantitative real-time polymerase chain reaction (qRT-PCR). Subsequently, evolutionary analysis and conserved sequences analysis of candidate genes were conducted. Among the 135,324 unigenes, 30,863 were shown to be differentially expressed, and eight randomly selected differentially expressed genes were expressed in the styles at 96 hours after SP and CP. The transcriptomics and qRT-PCR results were significantly correlated, which confirmed the reliability of the differentially expressed genes obtained in our study. Compared with SP96, six differentially expressed ribonuclease T2 family genes were obtained in CP96, which were considered candidates for S-RNase. Additionally, the spatiotemporal and organizational expression trends of six candidates for S-RNase were confirmed by qRT-PCR, and the evolutionary and conservative sequence analysis indicated six candidate S-RNases with the typical S-RNase structure. The spatiotemporal and organizational expression results and evolutionary and conservative sequence analyses of the six candidate S-RNases suggest that SI in V. ashei is likely an S-RNase-mediated gametophytic one. This finding suggests the involvement of novel, previously undiscovered components involved in the V. ashei SI system. These findings help elucidate the molecular mechanisms of SI in rabbiteye blueberry and may also benefit breeding, production, and genomics research in V. ashei and other Vaccinium species.

In recent years, the rapid alkalinization factor (RALF) family of cysteine-rich peptides has been reported to be crucial for several plant signaling mechanisms, including cell growth, plant immunity and fertilization. RALF4 and RALF19 (RALF4/19) pollen peptides redundantly regulate the pollen tube integrity and growth through binding to their receptors ANXUR1/2 (ANX1/2) and Buddha’s Paper Seal 1 and 2 (BUPS1/2), members of the Catharanthus roseus RLK1-like (CrRLK1L) family, and, thus, are essential for plant fertilization. However, the signaling mechanisms at the cellular level that follow these binding events remain unclear. In this study, we show that the addition of synthetic peptide RALF4 rapidly halts pollen tube growth along with the excessive deposition of plasma membrane and cell wall material at the tip. The ratiometric imaging of genetically encoded ROS and Ca2+ sensors-expressing pollen tubes shows that RALF4 treatment modulates the cytoplasmic levels of reactive oxygen species (ROS) and calcium (Ca2+) in opposite ways at the tip. Thus, we propose that pollen RALF4/19 peptides bind ANX1/2 and BUPS1/2 to regulate ROS and calcium homeostasis to ensure proper cell wall integrity and control of pollen tube growth.

Precise signalling between pollen tubes and synergid cells in the ovule initiates fertilization in flowering plants1. Contact of the pollen tube with the ovule triggers calcium spiking in the synergids2,3 that induces pollen tube rupture and sperm release. This process, termed pollen tube reception, entails the action of three synergid-expressed proteins in Arabidopsis: FERONIA (FER), a receptor-like kinase; LORELEI (LRE), a glycosylphosphatidylinositol-anchored protein; and NORTIA (NTA), a transmembrane protein of unknown function4-6. Genetic analyses have placed these three proteins in the same pathway; however, it remains unknown how they work together to enable synergid-pollen tube communication. Here we identify two pollen-tube-derived small peptides7 that belong to the rapid alkalinization factor (RALF) family8 as ligands for the FER-LRE co-receptor, which in turn recruits NTA to the plasma membrane. NTA functions as a calmodulin-gated calcium channel required for calcium spiking in the synergid. We also reconstitute the biochemical pathway in which FER-LRE perceives pollen-tube-derived peptides to activate the NTA calcium channel and initiate calcium spiking, a second messenger for pollen tube reception. The FER-LRE-NTA trio therefore forms a previously unanticipated receptor-channel complex in the female cell to recognize male signals and trigger the fertilization process.

ROPs (Rho of Plants) are plant specific small GTPases involved in many membrane patterning processes and play important roles in the establishment and communication of cell polarity. These small GTPases can produce a wide variety of patterns, ranging from a single cluster in tip-growing root hairs and pollen tubes to an oriented stripe pattern controlling protoxylem cell wall deposition. For an understanding of what controls these various patterns, models are indispensable. Consequently, many modelling studies on small GTPase patterning exist, often focusing on yeast or animal cells. Multiple patterns occurring in plants, however, require the stable co-existence of multiple active ROP clusters, which does not occur with the most common yeast/animal models. The possibility of such patterns critically depends on the precise model formulation. Additionally, different small GTPases are usually treated interchangeably in models, even though plants possess two types of ROPs with distinct molecular properties, one of which is unique to plants. Furthermore, the shape and even the type of ROP patterns may be affected by the cortical cytoskeleton, and cortex composition and anisotropy differ dramatically between plants and animals. Here, we review insights into ROP patterning from modelling efforts across kingdoms, as well as some outstanding questions arising from these models and recent experimental findings. [ABSTRACT FROM AUTHOR]

Pollen viability, dispersion ability and longevity during deep-freezer storage were studied in three Juniperus taxa distributed in Slovakia. All these characteristics of pollen are closely related to the pollination and/or fertilization success of the junipers in nature. Pollen viability varied considerably between the three populations of J. communis and one population of each, J. sibirica and J. communis var. intermedia. Pollen germination rate ranged between 40.75% and 75.06%, and pollen tube length between 30.32 and 40.41 µm. A clear tendency indicates a higher germination rate of J. communis pollen from lower altitudes and reduced germination of J. sibirica and J. communis var. intermedia pollen from higher altitudes. The dispersion potential of the J. communis pollen during its shedding seems relatively low. In 2021, pollen cloud density was diluted at 68.1% at the 4 m distance from the test shrub, in 2022 of 52.1% at the 17 m distance from the pollen source. A deep-freezer storage of juniper pollen in a double-walled polyethylene bag with silica gel was not efficient enough, as indicated by the drop of pollen germination rate of 31.2% in J. communis and of 79.4% in J. sibirica during a 1-year storage period at − 81 °C. [ABSTRACT FROM AUTHOR]

Polyphenol oxidases (PPOs) are type-3 copper enzymes and are involved in many biological processes. However, the potential functions of PPOs in pollination are not fully understood. In this work, we have screened 13 PPO members in Nicotiana. tabacum (named NtPPO1-13, NtPPOs) to explore their characteristics and functions in pollination. The results show that NtPPOs are closely related to PPOs in Solanaceae and share conserved domains except NtPPO4. Generally, NtPPOs are diversely expressed in different tissues and are distributed in pistil and male gametes. Specifically, NtPPO9 and NtPPO10 are highly expressed in the pistil and mature anther. In addition, the expression levels and enzyme activities of NtPPOs are increased after N. tabacum self-pollination. Knockdown of NtPPOs would affect pollen growth after pollination, and the purines and flavonoid compounds are accumulated in self-pollinated pistil. Altogether, our findings demonstrate that NtPPOs potentially play a role in the pollen tube growth after pollination through purines and flavonoid compounds, and will provide new insights into the role of PPOs in plant reproduction. [ABSTRACT FROM AUTHOR]