Identifying novel regulators of exocytosis through a chemical genetic screen in Arabidopsis
X. LI, C. ZHANG, C. J. STAIGER
Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907, USA
Center for Plant Biology, Purdue University, West Lafayette, IN 47907, USA
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA

Exocytosis is a process necessary for the efficient delivery of new membrane, membrane proteins, and extracellular matrix components to the plasma membrane (PM) and cell wall. The process encompasses packaging of cargo into secretory vesicles at the trans-Golgi network as well as their transport, tethering, docking, and fusion with the PM. The exocyst complex facilitates the tethering of secretory vesicles to the PM. A small molecule, Endosidin2 (ES2), serves as an exocyst inhibitor and binds to the EXO70A1 subunit of the exocyst complex. To identify additional exocytosis regulators, we carried out a forward chemical genetic screen to identify ES2-hypersensitive mutants from ethyl methanesulfonate (EMS)-mutagenized Arabidopsis lines. We developed a pipeline for the identification and mapping of drug-hypersensitive mutants, and obtained a fully sequenced and mapped EMS mutant population to be used for future studies. Mutants hypersensitive to ES2 were named es2s. One such mutant, es2s-15, had a strong ES2 hypersensitive phenotype for root. We mapped the causal mutation to argj and identified a second allele with similar phenotypes. Surprisingly, ArgJ is an enzyme in the arginine biosynthesis pathway. Supplementation with arginine rescued the ES2 hypersensitive phenotype of both argj alleles. Taken together, our results indicate that impaired arginine biosynthesis leads to exocytosis defects.