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PSIA: A Comprehensive Knowledgebase of Plant Self-incompatibility.

Self-incompatibility (SI) is an important genetic mechanism in angiosperms that prevents inbreeding and promotes outcrossing, with significant implications for crop breeding, including genetic diversity, hybrid seed production, and yield optimization. In eudicots, SI is typically governed by a single S-locus containing tightly linked pistil and pollen S-determinant genes. Despite major advances in SI research, a centralized, comprehensive resource for SI-related genomic data remains lacking. To address this gap, we developed the Plant Self-Incompatibility Atlas (PSIA), a systematically curated knowledgebase providing an extensive compilation of plant SI, including genomic resources for SI species, S gene annotations, molecular mechanisms, phylogenetic relationships, and comparative genomic analyses. The current release of PSIA includes over 500 genome assemblies from 469 SI species. Using known S genes as queries, we manually identified and rigorously curated 3700 S genes. PSIA provides detailed S-locus information from assembled genomes of SI species and offers an interactive platform for browsing, BLAST searches, S gene analysis, and data retrieval. Additionally, PSIA serves as a unique platform for comparative genomic studies of S-loci, facilitating exploration of the dynamic processes underlying the origin, loss, and regain of SI. As a comprehensive and user-friendly resource, PSIA will greatly advance our understanding of angiosperm SI and serve as a valuable tool for crop breeding and hybrid seed production. PSIA is freely available at http://www.plantsi.cn.

Self-Incompatibility in Flowering Plants

Self-incompatibility systems as bioassays for mutagens.

Many flowering plants are unable to set seeds with their own pollen because a system known as gametophytic self-incompatibility is operating. The basis of this system is a single multiallelic locus S, and if the S allele carried by a pollen grain matches one of the two S alleles carried in the style, as it is certain to do upon self-pollination, then pollen tube growth is inhibited. Should one of the self-pollen grains carry a mutated S allele, however, it would not match either of those carried in the style and would therefore, not be inhibited. Gametophytic self-incompatibility thus provides a mechanism for discriminating between such mutant and nonmutant pollen grains. Knowing the numbers of pollen grains available to the stigma, and also the numbers of seeds produced, it becomes possible to estimate the frequency with which mutations occur at the S locus. Assay systems of mutagenesis which employ gametophytic self incompatibility will allow very large numbers of pollen grains to be screened for S allele mutants, which should indicate the mutagenicity of the environment. These systems have the added benefit that screening is done by the stylar tissues, rather than technicians. Finally, they may be used to construct largely autonomous assay systems which would provide continuous monitoring of the environment.

Alleles

Genetic interactions and natural variation underlying S-RNase-independent unilateral incompatibility in Solanum.

Pistils of self-incompatible (SI) species/populations typically reject pollen of related self-compatible (SC) species/populations, but not vice versa, a pattern known as unilateral incompatibility (UI). UI is complex and includes both S-RNase-dependent and S-RNase-independent mechanisms. Pistils of Solanum pennellii LA0716 (SC, no S-RNase) reject pollen of cultivated tomato, Solanum lycopersicum (SC); UI in this system involves the expression of ornithine decarboxylase2 (ODC2) and HT-A/-B genes in the pistil, and farnesyl pyrophosphate synthase2 (FPS2), ui6.2, and ui12.2 in pollen. We show that IL12-3 (HT-A/-B) × IL3-3 (ODC2) double introgression lines reject S. lycopersicum pollen, while odc2 or ht-a mutants do not, demonstrating that ODC2 and HT-A are required for UI. Transmission ratio distortion in favor of pennellii alleles was observed in interspecific F2 S. lycopersicum × S. pennellii near ui6.2 and ui12.2, and in F2 IL12-3 × IL3-3 near ui12.2. Equivalent populations made with odc2 mutants segregate in Mendelian ratios, while ht-a mutants have little effect, indicating ui6.2 and ui12.2 interact primarily with ODC2. Pollen from fps2 mutants in S. pennellii LA0716 are incompatible on pistils of all tested S. pennellii and some Solanum habrochaites accessions, but compatible with all other tomato clade species, suggesting ODC2-dependent UI evolved in a common ancestor to S. pennellii and S. habrochaites. Within S. habrochaites, fps2 pollen rejection was observed mainly in SI or mixed mating populations, suggesting an association with outcrossing. Triple mutants of S. pennellii and S. habrochaites lacking functional ODC2, HT-A/-B, and S-RNase are cross-compatible as female parents with S. lycopersicum, allowing transfer of their cytoplasmic genomes into cultivated tomato.

Solanum