During evolution, new gene functions are created by the duplication and functional diversification of existing genes. Diversification can be at the level of transcriptional regulation or protein function. Kirik and co-workers now describe how for two paralogous MYB-related transcription factors –MYB23 and GL1 – functional diversification at both levels is involved in the development of branching hair-like structures on Arabidopsisleaves called trichomes (see ). Their study of trichomes in myb23 and gl1single and double mutants reveals that MYB23 controls trichome branching and trichome initiation at leaf edges, the latter redundantly with GL1. Promoter and protein-coding-region swap experiments indicate that, for trichome initiation, the diversification of gl1 and myb23 gene functions is determined only by how their expression is regulated. By contrast, the diversification of their functions with respect to trichome branching involves differences both in the regulation of the two genes and in the proteins they encode.
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