Interaction of SAUR53 and Its Close Homologs with Calmodulin May Play a Role in Early Development in Arabidopsis

Abstract

Auxin plays crucial roles in modulating various aspects of plant growth and development throughout the plant life cycle. At the molecular level, auxin rapidly upregulates the expression of many genes, including those belong to three primary auxin-responsive (PAR) gene families. Small auxin-up RNA (SAUR) family is the largest among the three PAR gene families and contains 81 genes; however, molecular and physiological functions of most of them are yet to be discovered. Recently, we showed that the ectopic expression of SAUR53 causes hyper-elongation of cells and organs and alters apical hook development in Arabidopsis. Here we show that SAUR53 and its three close homologs, SAUR42, SAUR52, and SAUR69, physically interact with calmodulin (CaM) through their N-terminal CaM-binding domains. Additionally, seedlings of all four SAUR overexpression (SAUR-OX) transgenic lines are less sensitive to CaM inhibitor mediated inhibition of primary root elongation. We also show that CaM inhibitors accelerate the apical hook opening in dark-grown, wild-type seedlings, similar to dark-grown SAUR53-OX seedlings. Collectively, our present work reveals molecular and physiological relationships between SAURs and CaM proteins.