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PCP-B class pollen coat proteins are key regulators of the hydration checkpoint in Arabidopsis thaliana pollen–stigma interactions
The establishment of pollen–pistil compatibility is strictly regulated by factors derived from both male and female reproductive structures. Highly diverse small cysteine-rich proteins (CRPs) have been found to play multiple roles in plant reproduction, including the earliest stages of the pollen–stigma interaction. Secreted CRPs found in the pollen coat of members of the Brassicaceae, the pollen coat proteins (PCPs), are emerging as important signalling molecules that regulate the pollen–stigma interaction.
Using a combination of protein characterization, expression and phylogenetic analyses we identified a novel class of Arabidopsis thaliana pollen-borne CRPs, the PCP-Bs (for pollen coat protein B-class) that are related to embryo surrounding factor (ESF1) developmental regulators. Single and multiple PCP-B mutant lines were utilized in bioassays to assess effects on pollen hydration, adhesion and pollen tube growth.
Our results revealed that pollen hydration is severely impaired when multiple PCP-Bs are lost from the pollen coat. The hydration defect also resulted in reduced pollen adhesion and delayed pollen tube growth in all mutants studied.
These results demonstrate that AtPCP-Bs are key regulators of the hydration ‘checkpoint’ in establishment of pollen–stigma compatibility. In addition, we propose that interspecies diversity of PCP-Bs may contribute to reproductive barriers in the Brassicaceae.
Journal Article
Pollen performance under controlled temperatures and chromosome stability of diploid and tetraploid citrus
Background
Polyploidization plays a major role in citrus breeding, particularly in generating triploid hybrids through controlled crosses between diploid female and tetraploid male parents. However, limited information is available on how polyploidy affects pollen performance in citrus, and in particular, how temperature influences these processes. In this study, we compared pollen viability under field conditions and pollen tube growth at different temperatures in diploid and tetraploid genotypes, and assessed whether the observed differences were related to genomic instability caused by the tetraploidization treatment.
Results
Tetraploid `Clemenules´ and `Fortune´, both colchicine-derived, showed a higher proportion of collapsed pollen grains and reduced viability compared with their diploid counterparts, whereas the spontaneous tetraploid `Pineapple´ displayed values similar to those of the diploid. Pollen tube growth assays revealed slightly faster tube elongation in tetraploids, and notably, self-incompatible diploid pistils of `Fortune´ were successfully fertilized by pollen from its tetraploid form. Genotyping-by-sequencing (GBS) analyses of diploid and tetraploid plants revealed no chromosomal rearrangements or dosage alterations, suggesting that colchicine treatment did not induce large-scale genomic instability.
Conclusions
Our findings demonstrate that tetraploidy influences several aspects of citrus pollen performance, while genomic stability remains largely preserved in colchicine-induced genotypes. These results provide new insights into the reproductive biology of citrus polyploids under different temperature scenarios and reinforce the potential use of tetraploid parents in triploid breeding programs.
Key message
Pollen grains of diploid and tetraploid citrus genotypes show a different performance, while there is no evidence of chromosomal instability during the tetraploidization process.
Journal Article
Meet me in the in-between
\"Growing up the middle child of transatlantic parents-her English Rose mother and cowboy boot-loving father-Bella Pollen never quite figured out how to belong. Restlessly crossing back and forth between the boundaries of family and freedom, England and America, home and away, she has sought but generally failed to contain an adventurous spirit within the confines of conventional living. When she awakes one morning in an existential panic, Pollen grudgingly concludes that in order to move forward, she needs to take a good look at her past. In Meet Me in the In-Between, Pollen takes us on the uproarious journey of a life, from her privileged, unorthodox childhood in Upper Manhattan through early marriage to a son of an alluring Mafioso, to the dusty border towns of Mexico where she embarks on a border crossing with some Pink Floyd-loving smugglers. Throughout all, Bella grapples intently with relationships, motherhood, career ups and downs, and a pathological fear of being boxed in. Interwoven with exquisite original illustrations by the award-winning Kate Boxer, this is a tender, funny, and poignantly honest story of one woman's quest to keep looking for the extraordinary in an ordinary life.\"-- Provided by publisher.
Book
Class XI Myosins Move Specific Organelles in Pollen Tubes and Are Required for Normal Fertility and Pollen Tube Growth in Arabidopsis
Pollen tube growth is an essential aspect of plant reproduction because it is the mechanism through which nonmotile sperm cells are delivered to ovules, thus allowing fertilization to occur. A pollen tube is a single cell that only grows at the tip, and this tip growth has been shown to depend on actin filaments. It is generally assumed that myosin-driven movements along these actin filaments are required to sustain the high growth rates of pollen tubes. We tested this conjecture by examining seed set, pollen fitness, and pollen tube growth for knockout mutants of five of the six myosin XI genes expressed in pollen of Arabidopsis (Arabidopsis thaliana). Single mutants had little or no reduction in overall fertility, whereas double mutants of highly similar pollen myosins had greater defects in pollen tube growth. In particular,myo11c1
myo11c2pollen tubes grew more slowly than wild-type pollen tubes, which resulted in reduced fitness compared with the wild type and a drastic reduction in seed set. Golgi stack and peroxisome movements were also significantly reduced, and actin filaments were less organized inmyo11c1
myo11c2pollen tubes. Interestingly, the movement of yellow fluorescent protein-RabA4d-labeled vesicles and their accumulation at pollen tube tips were not affected in themyo11c1
myo11c2double mutant, demonstrating functional specialization among myosin isoforms. We conclude that class XI myosins are required for organelle motility, actin organization, and optimal growth of pollen tubes.
Journal Article
OsAP65, a rice aspartic protease, is essential for male fertility and plays a role in pollen germination and pollen tube growth
Aspartic proteases (APs) comprise a large proteolytic enzyme family widely distributed in animals, microbes, viruses, and plants. The rice genome encodes 96 APs, of which only a few have been functionally characterized. Here, the identification and characterization of a novel AP gene, OsAP65, which plays an indispensable role in pollen tube growth in rice, is reported. The T-DNA insertion line of OsAP65 caused severe segregation distortion. In the progeny derived from an individual heterozygous for the T-DNA insertion, the wild type and T-DNA-carrying heterozygote segregated at a ratio close to 1:1, while homozygotes of disrupted OsAP65 (OsAP65–/–) were not recovered. Reciprocal crosses between heterozygotes and wild-type plants demonstrated that the mutant alleles could not be transmitted through the male gamete. Examination of the anthers from heterozygous plants revealed that the mutant pollen matured normally, but did not germinate or elongate. OsAP65 was expressed in various tissues and the transcript level in heterozygous plants was about half of the amount measured in the wild-type plants. The subcellular localization showed that OsAP65 is a pre-vacuolar compartment (PVC) protein. These results indicated that OsAP65 was essential for rice pollen germination and tube growth.
Journal Article
LRX Proteins Play a Crucial Role in Pollen Grain and Pollen Tube Cell Wall Development
Leu-rich repeat extensins (LRXs) are chimeric proteins containing an N-terminal Leu-rich repeat (LRR) and a C-terminal extensin domain. LRXs are involved in cell wall formation in vegetative tissues and required for plant growth. However, the nature of their role in these cellular processes remains to be elucidated. Here, we used a combination of molecular techniques, light microscopy, and transmission electron microscopy to characterize mutants of pollen-expressed LRXs in Arabidopsis (Arabidopsis thaliana). Mutations in multiple pollen-expressed lrx genes cause severe defects in pollen germination and pollen tube growth, resulting in a reduced seed set. Physiological experiments demonstrate that manipulating Ca²⁺ availability partially suppresses the pollen tube growth defects, suggesting that LRX proteins influence Ca²⁺-related processes. Furthermore, we show that LRX protein localizes to the cell wall, and its LRR-domain (which likely mediates protein-protein interactions) is associated with the plasma membrane. Mechanical analyses by cellular force microscopy and finite element method-based modeling revealed significant changes in the material properties of the cell wall and the fine-tuning of cellular biophysical parameters in the mutants compared to the wild type. The results indicate that LRX proteins might play a role in cell wall-plasma membrane communication, influencing cell wall formation and cellular mechanics.
Journal Article
Self-(in)compatibility in Tunisian apple accessions Malus domestica. Borkh: S-genotypes identification and pollen tube growth analysis
Main conclusionSelf-incompatibility studies have revealed a potential use of Tunisian apple resources for crop improvement and modern breeding programs and a likely correlation between the pollen tube growth and flowering period.AbstractssApples [Malus domestica. Borkh] exhibit an S-RNase-based gametophytic self-incompatibility (GSI) system. Four primer combinations were used to S-genotype eighteen Tunisian local apple accessions and twelve introduced accessions that served as references. Within the Tunisian local accessions, S2, S3, S7, and S28 S-alleles were the most frequent and were assigned to 14 S-genotypes; among them, S7S28, S3S7, S2S5, and S2S3 were the most abundant. PCA plot showed that population structuring was affected by the S-alleles frequencies and revealed a modern origin of the Tunisian varieties rather than being ancient ones. Nonetheless, the results obtained with 17 SSR markers showed a separate grouping of local Tunisian accessions that calls into question the hypothesis discussed. Pollination experiments showed that the pollen started to germinate within 24 h of pollination but 48 h after pollination in the “El Fessi” accession. The first pollen tubes arrived in the styles within 36 h of pollination in two early flowering accessions known as “Arbi” and “Bokri”, and after 72 h of pollination in late flowering “El Fessi” and 48 h after pollination in remaining accessions. The first pollen tube arrests were observed in accessions “Arbi” and “Bokri” within 84 h of pollination, within 108 h of pollination in “El Fessi” and within 108 h of pollination in remaining accessions. In the apple accession called “Boutabgaya,” the pollen tubes reached the base of the style within 120 h of pollination without being aborted. Nevertheless, the self-compatible nature of “Boutabgaya” needs more studies to be confirmed. However, our results revealed the malfunction of the female component of the GSI in this accession. To conclude, this work paved the path for further studies to enhance the insight (i) into the relation between the flowering period and the pollen tube growth, (ii) self-compatible nature of “Boutabgaya”, and (iii) the origin of the Tunisian apple.
Journal Article