Opposite roles of group IV BBX proteins: Exploring missing links between structural and functional diversity.

BBX proteins are a family of zinc finger transcription factors that are versatile regulators of plant development. The 32 BBX proteins in Arabidopsis are subdivided into five structural groups based on their domain structure. Members of group IV play important and diverse roles in light-regulated development. The N-terminal B-box domains mediate DNA binding and transcriptional regulation. The C-terminal region determines the functional diversity of the structurally similar group IV members as reported in our recent study investigating the basis of functional diversification between BBX21 and BBX24. We also found that multi-layered regulation of HY5 by the BBX proteins leads to a diverse repertoire of developmental effects. Here we provide a comprehensive structure-function analysis of the group IV BBX proteins.