Genetic Diversity of Genes Controlling Unilateral Incompatibility in Japanese Cultivars of Chinese Cabbage

In recent years, unilateral incompatibility (UI), which is an incompatibility system for recognizing and rejecting foreign pollen that operates in one direction, has been shown to be closely related to self-incompatibility (SI) in Brassica rapa. The stigma- and pollen-side recognition factors (SUI1 and PUI1, respectively) of this UI are similar to those of SI (stigma-side SRK and pollen-side SP11), indicating that SUI1 and PUI1 interact with each other and cause pollen-pistil incompatibility only when a specific genotype is pollinated. To clarify the genetic diversity of SUI1 and PUI1 in Japanese B. rapa, here we investigated the UI phenotype and the SUI1/PUI1 sequences in Japanese commercial varieties of Chinese cabbage. The present study showed that multiple copies of nonfunctional PUI1 were located within and in the vicinity of the UI locus region, and that the functional SUI1 was highly conserved in Chinese cabbage. In addition, we found a novel nonfunctional SUI1 allele with a dominant negative effect on the functional SUI1 allele in the heterozygote.

Callose depositions underlie the incompatible reaction in intergeneric crosses of rice

Distant hybridization of cereals is often impaired by fertilization barriers. Haploid induction through intergeneric crossing is well developed in wheat but has not been successful in rice due to incompatibility issues. The present study was thus undertaken to identify fertilization barriers that hinder the compatibility of the rice cultivar Punjab Rice 121 with maize and pearl millet lines as pollinators. A total of 37,357 spikelets were pollinated, yielding 494 caryopses upon supplementation with auxins. The resultant caryopses, arising from true intergeneric crosses, lacked embryos. Imaging of the pollinated pistils at different intervals indicated that intense callose depositions block the release of generative nuclei to the ovule in these wide crosses. Rice spikelets pollinated with rice pollen (cis-generic crosses) exhibited positive indicators of fertilization reaction at the micropyle. While the cis-generic crosses initiated true caryopsis formation after 24 h, no comparative reaction was observed in the intergeneric crosses. The current survey underlines that the rice female gametophyte presents a strong pre-fertilization barrier to foreign pollen. This barrier may be modulated in the future by altering genotype and auxin combinations.

Paternity Assignment in White Guinea Yam (Dioscorea Rotundata) Half-Sib Progenies from Polycross Mating Design Using SNP Markers

White Guinea yam is mostly a dioecious outcrossing crop with male and female flowers produced on distinct plants. Fertile parents produce high fruit set in an open pollination polycross block, which is a cost-effective and convenient way of generating variability in yam breeding. However, the pollen parent of progeny from polycross mating is usually unknown. This study aimed to determine paternity in white Guinea yam half-sib progenies from polycross mating design. A total of 394 half-sib progenies from random open pollination involving nine female and three male parents was genotyped with 6602 SNP markers from DArTSeq platform to recover full pedigree. A higher proportion of expected heterozygosity, allelic richness, and evenness were observed in the half-sib progenies. A complete pedigree was established for all progenies from two families (TDr1685 and TDr1688) with 100% accuracy, while in the remaining families, paternity was assigned successfully only for 56 to 98% of the progenies. Our results indicated unequal paternal contribution under natural open pollination in yam, suggesting unequal pollen migrations or gene flow among the crossing parents. A total of 3.8% of progenies lacking paternal identity due to foreign pollen contamination outside the polycross block was observed. This study established the efficient determination of parental reconstruction and allelic contributions in the white Guinea yam half-sib progenies generated from open pollination polycross using SNP markers. Findings are useful for parental reconstruction, accurate dissection of the genetic effects, and selection in white Guinea yam breeding program utilizing polycross mating design.

Recipient and donor characteristics govern the hierarchical structure of heterospecific pollen competition networks

SUMMARYPollinator sharing can have negative consequences for plant fitness with the arrival of foreign pollen, yet responses are often variable among species. Plant traits and relatedness of donor and recipient species have been suggested to drive the variations in plant fitness, but how they shape the structure of pollen competition networks has been overlooked at the community level.To understand the importance of traits and relatedness we conducted a controlled glasshouse experiment with an artificial co-flowering community. We performed 900 reciprocal crosses by experimentally transferring pollen among 10 species belonging to three different plant families.We found a significant reduction in seed set for 67% of the crosses, driven largely by recipient traits and the interaction between recipient-donor traits under specific circumstances of trait-matching. These traits and their asymmetries among species led to a hierarchical (or transitive) structure of pollen competition with clear winners and losers depending on specific combination of traits.A greater understanding of the importance of trait matching and asymmetries among donor and recipient plant species will facilitate knowledge of the mechanisms underlying foreign pollen impacts upon plant reproductive fitness. This will require a shift from pairwise to community level interactions.

Arabidopsis ECERIFERUM3 (CER3) Plays a Critical Role in Maintaining Hydration for Pollen-Stigma Recognition during Fertilization

ABSTRACTPlants distinguish the pollen grains that land on their stigmas, only allowing compatible pollen to fertilize female gametes. To analyze the underlying mechanism, conditional male-sterile mutations with affected pollen coat and disrupted pollen-stigma recognition were isolated and described. The mutant pollen failed to germinate, but germinated in vitro, suggesting that they are viable. In mutants, stigma cells that contacted their own pollen generated callose, a carbohydrate produced in response to foreign pollen. High humidity restored pollen hydration and successful fertilization, indicating defective dehydration in pollen-stigma interaction. Further analysis results from mixed pollination experiments demonstrated that the mutant pollen specifically lacked a functional pollen-stigma recognition system. The sterile plants lacked stem waxes and displayed postgenital fusion between aerial floral organs. In addition, the mutant pollen was deficient in long-chain lipids and had excess tryphine. Transmission electron microscopy observation showed that mutant pollen had almost the same surface structure as the wild type at bicellular pollen stage. However, abnormal plastoglobuli were observed in the plastids of the mutant tapetum, which was indicative of altered lipid accumulation. CER3 transcript was found in anther tapetum and microspores at development stage 9 while CER3-GFP fusion protein was localized to the cell plasma membrane. Our data reveal that CER3 is required for biosynthesis of tryphine lipids which play a critical role in maintaining hydration for pollen-stigma recognition during fertilization.

Molecular Tracing of the Origin of Six Different Plant Species in Bee Honey Using Real-Time PCR

The quality of honey is significantly influenced by floralorigin. Mislabeling floral species occurs frequently in bee honey products. To protect consumers from economic fraud and maintain a fair market environment, methods to identify floralspecies in honey are necessary. In our study, real-time PCRs were established, targeting six honey types mainly produced in China (canola, Chinese milkvetch, Chinese chaste tree, locust tree, litchi, and longan). Sensitivity testing on DNA fromplant tissues exhibited LODs of about 0.5–5 pg/μL. For DNA extracts of pollen sediments from different honeyspecies, LODs ranged from 13.6 to 403.2 pg/μL. In an experiment to determine the practical LODs of honey in which adulterant honey was spiked in the genuine honey, adulterant honey as low as about 0.1–0.5% was detected in 90–100% in 10 parallel tests. Additionally, pollen was spiked in the honey and stored under various conditions to investigate the migration of pollen DNA into the honey supernatant. Finally, the efficiency of our method was investigated by testing honey samples of unknown compositions from different geographic regions. Of the 159 honey samples that were supposed tobe monofloral that had been collected in five provinces, a small portion were found to be contaminated with foreign pollen(7%). The methods proved to be specific, sensitive, and reliable in identifying the six plant species in honey, which would be a useful tool during the market supervision and QC of honey products.

In Situ Pollen Germination and Artificial Pollination Compatibility in Cassava (Manihot esculenta Crantz)

Cassava cultivars are self-compatible, sufficient pollination and fertilization are important factors affecting the rate of fruit set and fruit quality, but the effects of compatible pollination relationships on cassava pollen development and fruit set are poorly understood. In the present study, in situ pollen germination and compatible relationship were investigated by using self-pollination and cross-pollination between two cassava cultivars (SC5 and SC7). The observation in situ pollen germination was carried out with toluidine blue staining method under the fluorescence microscope. The result shows that after self-pollination for 20 min, the pollens, released from SC5 anthers, started to produce pollen tubes and the maximum germination rate (GR) was 39.2%. It cost 60 min for the pollen tubes carrying sperm cells to penetrate through the pistil extracellular matrices of the transmitting tract to the ovary. However, after cross-pollination for 10 min, the pollens started to germinate and maximum GR was 66.8%. It took 30 min for the pollen tube trip to reach ovary. Additionally, the analysis of fruit set indicated that pollination compatibility in cross-pollination was significantly higher than that in self-pollination. This work provided cassava cross breeding a clue that foreign pollen may facilitate fertilization and increase fruit set.

Paternity Analysis of the Olive Variety “Istrska Belica” and Identification of Pollen Donors by Microsatellite Markers

The leading olive variety in Slovenia is “Istrska belica” (Olea europaeaL.), which currently represents 70% of all olive trees in productive orchards. Paternity analysis based on microsatellite markers was used for genotyping and identification of the potential pollen donors of “Istrska belica” and for assessing the proportion of self-fertilization in monovarietal olive orchards in the Slovene Istria. Seven microsatellite loci were used for genotyping thirty-one olive embryos from “Istrska belica” trees and for all potential pollen donor varieties, which are grown in the region and could participate as pollinators. Genotyping results and allele identification were performed using the FaMoz software. The most probable pollen donor was assigned to 39% of all analyzed embryos. Among all analyzed embryos no single case of self-fertilization was confirmed. According to the present results, the variety “Istrska belica” was in all cases fertilized by foreign pollen. The results will contribute to defining the new guidelines for farmers regarding the proper management and growing practice in monovarietal olive groves.