Arabidopsis thaliana MYB5 collaborates with TRANSPARENT TESTA GLABRA1 (TTG1) and basic-Helix-Loop-Helix (bHLH) transcription factors to regulate seed coat, trichome and root cell differentiation. Using a yeast two-hybrid system we show that the N-terminal region of MYB5 binds directly to the serine/threonine CASEIN KINASE2 BETA3 (CK2β3) subunit. Functions of the CASEIN KINASE2 (CK2) complex include facilitating phosphorylation of MYB transcription factors and cell cycle checkpoint regulatory proteins. Purified recombinant MYB5 protein was found to bind only weakly in vitro to the promoter of ALPHA/BETA ESTERASE/HYDROLASE4 (ABE4), a known MYB5 target gene. We propose that phosphorylation of MYB5 facilitated by the MYB5-CK2β3 interaction enhances MYB5 binding to its target gene promoters.
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