The Calmodulin-Like Protein CML42 is Involved in Trichome Branching in Arabidopsis

Abstract

The Snedden lab has been studying a family of Ca2+-binding proteins from Arabidopsis that are related to the prototypical Ca2+ sensor calmodulin (CaM) and are termed CMLs (CaM-like proteins). Previous work on CML42 demonstrated that it displays biochemical properties typical of Ca2+ sensors and interacts in vitro with KIC (KCBP-interacting Ca2+-binding protein), a protein known to function in trichome branching. In the present study, I investigated whether CML42 is also involved in trichome branching. I examined a CML42 T-DNA insertion knockout line (cml42) and found that it exhibits a mutant trichome phenotype with increased branch numbers compared to wildtype plants. All other aspects of cml42 growth and morphology, including root hairs, appeared normal relative to wildtype plants. kic knockout plants did not show any discernible trichome phenotype when compared to wildtype plants, nor did transgenic lines overexpressing CML42. Transgenic plants lacking both CML42 and KIC expression (cml42kic) displayed a cml42 mutant phenotype. The genetic studies suggest that CML42 is a negative regulator of trichome branching. Biochemical analysis on recombinant full-length CML42, C-terminal, and N-terminal fragments, using the fluorescent probe 8-Anilino-1-naphthalenesulfonate (ANS), demonstrated that Ca2+-binding results in a conformational change in CML42 and the exposure of hydrophobic regions, particularly within the C-terminal lobe. Collectively, data from the Snedden Lab support the important role of Ca2+ signalling in trichome branching and morphology.