Phenotypic, genetic and molecular characterization of 7B-1, a conditional male-sterile mutant in tomato.

KEY MESSAGE: We characterized the photoperiod-sensitive 7B - 1 male-sterile mutant in tomato, showing its allelism with stamenless - 2 . Mapping experiments indicated SlGLO2 , a B-class MADS-box family member, as a strong candidate to underlie the 7B - 1 mutation. The interest in male sterility (MS) dates back to a long time due to its perspective use in hybrid seed production. Here, we characterize 7B-1, a photoperiod-sensitive male-sterile (ms) mutant in tomato (Solanum lycopersicum L.), in which stamens are restored to fertility by permissive growth conditions in short days (SD). This system represents a useful strategy to facilitate the maintenance of the ms line. Examination of 7B-1 and other structural mutants, vms, sl, sl-2 and tap3, showed carpellization of stamens in the third floral whorl. 7B-1 exhibits strong expressivity in long days (LD), producing 100% aberrant anthers and virtually no seed production under open pollination, whereas it recovered fertility in SD. By genetic analysis, we demonstrate that 7B-1 is not allelic to sl nor to vms; instead it shows allelism to sl-2. Because the homeotic phenotype of the mutation resembles lesions to members of the B-class MADS-box transcription factor family, that specify petal and stamen identity, we pursued a candidate gene approach towards these targets. Using an interspecific backcross mapping population and markers linked to B-class MADS-box genes, significant linkage was found between 7B-1 and the SlGLO2 gene on Chr6. This result was supported by the 7B-1 phenotype that is similar to that of SlGLO2 knock outs and by the strong downregulation of the gene in the mutant. Although the lesion underlying the mutant phenotype is still elusive, our results pave the way for the final demonstration that SlGLO2 underlies 7B-1 and further the use of 7B-1 mutant in tomato hybrid seed production schemes.