Auxin methylation is required for differential growth in Arabidopsis

Plants need to navigate and adjust their growth according to the environmental clues, such as light or gravity. Asymmetric distribution of auxin is necessary for organ bending. Abbas and colleagues show that conversion of indole-3-acetic acid (IAA) into methyl-IAA (Me-IAA) is important for asymmetric auxin distribution. Mutation of IAA carboxyl methyltransferase 1 (IAMT1) resulted in decreased in Me-IAA and impaired response to gravity stimulation. The iamt1 mutants exhibited higher auxin transport and their gravity response could be rescued by using low concentrations of auxin-transport inhibitor (NPA). Higher expression of auxin transporters (PIN) and reduced re-localization in response to gravity stimulus explains the reduced gravity response of the iamt1 mutants. The rescue of auxin methylation specifically in the endodermis rescued the agravitropic phenotype of iamt1 mutants. (Summary by Magdalena Julkowska) PNAS Proc. Natl. Acad. Sci. USA 10.1073/pnas.1806565115