Characterisation of the R2R3 Myb subgroup 9 family of transcription factors in tomato

Tomato (Solanum lycopersicum) has many epidermal cell outgrowths including conical cells and multiple types of trichomes. These include the anther-specific trichome mesh which holds the anthers connate. The R2R3 Myb Subgroup 9 family of transcription factors is involved in development of epidermal cell outgrowths throughout the angiosperms. No previous study has examined all members of this transcription factor family in a single species. All 7 R2R3 Myb Subgroup 9 genes were isolated from tomato. They were ectopically expressed in tobacco to assess their ability to induce epidermal cell outgrowth. Endogenous expression patterns were examined by semi-quantitative RT-PCR at different stages of floral development relative to the development of anther trichomes. We report variation in the degree of epidermal cell outgrowth produced in transgenic tobacco for each ectopically expressed gene. Based on expression profile and ectopic activity, SlMIXTA-2 is likely involved in the production of leaf trichomes while SlMYB17-2 is the best candidate for the regulation of the anther trichome mesh. Analysis of the phenotypes of transgenic plants ectopically expressing all 7 genes has revealed the different extent to which members of the same transcription factor subfamily can induce cellular outgrowth.