Transcriptional and hormonal regulation of petal and stamen development by STAMENLESS, the tomato (Solanum lycopersicum L.) orthologue to the B-class APETALA3 gene

Four B-class MADS box genes specify petal and stamen identities in tomato. However, several mutants showing homeotic changes affecting petal and stamen identities were described in tomato but the causal mutations have not been identified for most of them. In this paper, we characterized a strong stamenless mutant in the Primabel cultivar (sl-Pr) that exhibited homeotic conversion of petals in sepals and stamens in carpels and we compared it with the stamenless mutant in the LA0269 accession (sl-LA0269). Both sl mutants were allelic and sequencing revealed point mutations in the sl-Pr genome, leading to a truncated protein and a chromosomal rearrangement in the promoter region of the sl-LA0269 allele. Moreover, the floral phenotype of TAP3 antisense plants exhibited identical homeotic changes to sl mutants. These results demonstrate that SL is the tomato APETALA3 orthologue and that the mutant phenotype correlated to the SL silencing level. Expression analyses revealed that the sl-Pr mutation do not affect the other B gene expressions in the tomato flower, although SL may repress the A class gene MACROCALYX. The floral meristem identity genes FALSIFLORA and ANANTHA were demonstrated to act as upstream activators of B class genes in tomato. A partial reversion of the sl phenotype by gibberellins, gene expression analysis and hormone quantification in sl flowers revealed a role of phytohormones in flower development downstream of the SL gene. Together, our results indicated that petal and stamen identity in tomato depends on gene-hormone interactions, as mediated by the SL gene.