B-class MADS-box TM6 is a candidate gene for tomato male sterile-15²⁶

Tomato male sterile-15²⁶ locus was fine-mapped to an interval of 44.6 kb, and a B-class MADS-box gene TM6 was identified as the candidate gene. Male sterile lines have been widely used for hybrid seed production in many crop plants. The tomato male sterile-15²⁶ (ms-15²⁶) mutant displays abnormal stamens and exerted stigmas and is suitable for practical use. In this study, the ms-15²⁶ locus was fine-mapped to a 44.6 kb interval that contained four putative genes. Thereinto, Solyc02g084630 encodes tomato B-class MADS-box gene TM6 (syn. TDR6), which plays an important role in stamen development. Sequencing revealed that there was a 12.7 kb deletion in the ms-15²⁶ region, where the promoter and first four exons of the TM6 gene were absent. ms-15⁴⁷, an allele of ms-15²⁶, also contained the same deletion in the TM6 gene. And the other allele ms-15 mutant contained a single-nucleotide polymorphism (SNP, C to A) in the coding region of the TM6 gene, which led to a missense mutation (G to W). The codominant insertion/deletion (InDel) marker MS26D and codominant derived cleaved amplified polymorphic sequence (dCAPS) marker MS15C were developed based on the deletion and SNP, respectively. A real-time quantitative reverse-transcription PCR showed that expression of the TM6 gene was barely detectable in the flowers of the ms-15²⁶ and ms-15⁴⁷ mutants. In addition, other floral organ identity genes, pollen development marker genes, and pistil marker genes were differentially expressed between wild type and mutant flowers. These findings may facilitate functional analysis of the TM6 gene and help in the marker-assisted selection of ms-15 and its alleles in tomato breeding.