TTG1 proteins regulate circadian activity as well as epidermal cell fate and pigmentation.

Abstract

The Arabidopsis genome contains three members of the TTG1 (TRANSPARENT TESTA GLABRA 1) WDR subgroup of the WDR family, with very different reported roles. TTG1 is a regulator of epidermal cell differentiation, and of the production of pigments, while LWD1 (LIGHT-REGULATED WD1) and LWD2 (LIGHT-REGULATED WD2) are regulators of the circadian clock. We discovered a new central role for TTG1 WDR proteins as regulators of the circadian system, demonstrated by a lack of detectable circadian rhythms in a triple lwd1lwd2ttg1 mutant. We have demonstrated that there has been subfunctionalisation by protein changes within the angiosperms, with some TTG1 WDR proteins developing a stronger role in circadian clock regulation while losing the protein characteristics essential for pigment production and epidermal cell specification, and others weakening their ability to drive circadian clock regulation. Our work demonstrates that even where proteins are very conserved, small changes can drive big functional differences.