Heterologous myb genes distinct from GL1 enhance trichome production when overexpressed in Nicotiana tabacum

Myb-class transcription factors implicated in cell shape regulation were ov erexpressed in Arabidopsis thaliana and Nicotiana tabacum in an attempt to assess the extent to which cellular differentiation programs might be share d between these distantly related plants. GLABROUS I, a myb gene required f or trichome development in Arabidopsis, did not alter the trichome phenotyp e of the tobacco plants in which it was overexpressed, MIXTA, which in Anti rrhinum majus is reported to regulate certain aspects of floral papillae de velopment, did not complement the glabrous I mutant of Arabidopsis. However , 35S:MIXTA transformants of N. tabacum displayed various developmental abn ormalities, most strikingly production of supernumerary trichomes on cotyle dons, leaves and stems, In addition, floral papillae were converted to mult icellular trichomes, CotMYBA, a myb gene which is expressed in Gossypium hi rsutum ovules and has some homology to MIXTA, was also overexpressed in the two species. A similar but distinct syndrome of abnormalities, including t he production of cotyledonary trichomes, was observed in 35S:CotMYBA tobacc o transformants, However, CotMYBA did not alter trichome production in Arab idopsis. These results suggest that the trichomes of Arabidopsis and Nicoti ana are merely analogous structures, and that the myb genes regulating thei r differentiation are specific and separate.