Membrane Lipid Binding of ARC5 is Essential for Chloroplast Division and Developmentally Regulated

Abstract

ARC5 is a member of the dynamin-like protein family of membrane-interacting proteins named for dynamin, a membrane-constricting GTPase that polymerizes and binds to membranes through its pleckstrin homology (PH) domain. ARC5 participates in chloroplast division through an unknown mechanism. In this study, we showed that the PH domain of ARC5, which is divergent from those of other dynamin-related proteins, mainly binds to the membrane lipid PI3P in Arabidopsis thaliana. This binding activity is important for ARC5 function and chloroplast division. During evolution, an alternatively spliced intron that encodes a portion of the ARC5 PH domain arose in seed plants. Our functional analysis suggested that the shorter isoform of ARC5 (ARC5-S) is more active in chloroplast division than the longer isoform (ARC5-L). Dividing chloroplasts in plants with only ARC5-S are shorter and have steeper division furrows. ARC5-S binds to PI3P, PI4P, and PI5P more strongly than ARC5-L and is more abundant in most plant tissues, while the overall level of ARC5 and the proportion of ARC5-S are higher in fast-growing tissues. Thus, our results suggest that ARC5 is a membrane remodeling protein and that alternative splicing of ARC5 transcripts regulates chloroplast division to meet the needs of the evolution and development of seed plants.