A 163-bp insertion in the Capana10g000198 encoding a MYB transcription factor causes male sterility in pepper (Capsicum annuum L.).

Male sterility provides an efficient approach for commercial exploitation of heterosis. Despite more than 20 genic male sterile (GMS) mutants documented in pepper (Capsicum annuum L.), only two causal genes have been successfully identified. Here, a novel spontaneous recessive GMS mutant, designated msc-3, is identified and characterized at both phenotypic and histological levels. Pollen abortion of msc-3 mutant may be due to the delayed tapetum degradation, leading to the non-degeneration of tetrads callosic wall. Then, a modified MutMap method and molecular marker linkage analysis were employed to fine mapping the msc-3 locus, which was delimited to the ~139.91-kb region harboring 10 annotated genes. Gene expression and structure variation analyses indicate the Capana10g000198, encoding a R2R3-MYB transcription factor, is the best candidate gene for the msc-3 locus. Expression profiling analysis shows the Capana10g000198 is an anther-specific gene, and a 163-bp insertion in the Capana10g000198 is highly correlated with the male sterile (MS) phenotype. Additionally, downregulation of Capana10g000198 in male fertile plants through virus-induced gene silencing resulted in male sterility. Finally, possible regulatory relationships of the msc-3 gene with the other two reported pepper GMS genes, msc-1 and msc-2, have been studied, and comparative transcriptome analysis reveals the expression of 16 GMS homologs are significantly downregulated in the MS anthers. Overall, our results reveal that Capana10g000198 is the causal gene underlying the msc-3 locus, providing important theoretical clues and basis for further in-depth study on the regulatory mechanisms of pollen development in pepper.

Fine mapping and gene silencing pinpoint Capana10g002229 as a strong candidate gene regulating the deciduous character of ripe pepper fruit (Capsicum spp.).

KEY MESSAGE: The pepper S locus, which controls the deciduous character of ripe fruit, was first fine mapped into an interval with a physical length of ~ 38.03 kb on chromosome P10. Capana10g002229, encoding a polygalacturonase, was proposed as a strong candidate gene based on sequence comparison, expression pattern analysis and virus-induced gene silencing (VIGS). The deciduous character of ripe fruit, which is controlled by the dominant S locus, is a domesticated trait with potential value in the pepper processing industry (Capsicum spp.). However, the gene associated with the S locus has not been identified. Here, one major QTL designated S10.1 was detected by using the F2 population (n = 155) derived from BA3 (Capsicum annuum) × YNXML (Capsicum frutescens) and was further verified in an intraspecific backcross population (n = 254) derived from the cross between BB3 (C. annuum) and its wild relative Chiltepin (C. annuum var. glabriusculum) with BB3 as the recurrent parent. Then, a large BC1F2 population derived from the self-pollination of BB3 × (BB3 × Chiltepin) individuals and comprising 4217 individuals was used to screen the recombinants, and the S locus was ultimately delimited into a 38.03-kb region on chromosome P10 harbouring four annotated genes. Capana10g002229, encoding a polygalacturonase (PG), was proposed as the best candidate gene for S based on sequence comparison and expression pattern analyses. Downregulation of Capana10g002229 in fruits through VIGS significantly delayed fruit softening and abscission from the fruit-receptacle junction. Taken together, the results show that Capana10g002229 could be regarded as a strong candidate gene associated with the S locus in pepper. These findings not only lay a foundation for deciphering the molecular mechanisms underlying pepper domestication but also provide a strategy for genetic improvement of the deciduous character of ripe fruit using a marker-assisted selection approach.