Mapping the candidate gene controlling male sterility using EMS-mutagenized mutant smms1 in eggplant (Solanum melongena L.)

Male sterility (MS) is a desirable tool for hybrid seed production. Eggplant is one of the most widely grown fruit vegetables all over the world. Although a lot of male-sterile lines were created in eggplant, the genes underlying the MS regulation in eggplant remain largely unknown. EMS (ethyl methane sulfonate)- mutagenized mutant is an ideal material for the identification of genes regulating MS in eggplant. In the present study, we identified a mutant, named smms1 (Solanum melongena male sterility 1) with smaller flowers and abnormal anthers. Further analyses indicated the pollens in smms1 showed highly vacuolated and significant decreased number, size and viability compared to wild type (WT). Bulked segregant analysis sequencing (BSA-seq) and Mutmap analyses identified a G-to-A mutation in an alternative splicing region in the 2nd intron of Smechr0501647. Smechr0501647 encodes a subunit of Mediator (MED) that functions as a bridge between transcription factors and RNA polymerase II. The SNP results in three splicing events with 11 bp and 15 bp deletion in the 2nd exon and the retention of the 1st intron. Notably, the events with 11 bp deletion and intron retention led to premature stop codons. Gene Ontology (GO) enrichment of Differentially expressed gene (DEG) suggested that while up-regulated DEGs in smms1 are enriched in phytohormone related processes, the enriched GO terms of down-regulated DEGs were mainly related to cellular processes. The measurement of the phytohormone contents in WT and smms1 indicated the involvement of the abscisic acid (ABA), indole-3-acetic acid (IAA), salicylic acid (SA), jasmonic acid (JA) and cytokinins (CKs) in the MS regulation mediated by SmMS1 in eggplant. The discovery of the candidate gene controlling MS not only provides a potential target for the molecular breeding of MS germplasms, but also provides an effective basis of for studying regulatory mechanisms of MS in eggplant.