Arabidopsis PIP5K2 Is Involved in Root Gravitropism Through Regulation of Polar Auxin Transport

Abstract

Root gravitropism is a well-documented process regulated by auxin, especially polar auxin transport, which is mediated by membrane localized auxin influx and efflux carriers. The impact of PIP5K2 deficiency on root gravitropism was tested, which revealed a positive role of PIP5K2 in root gravity response. This is considered not caused by reduced auxin accumulation since exogenous auxin cannot rescue the reduced gravity response phenotype in pip5k2. Altered sensitivity to auxin transport inhibitor NPA confirmed the involvement of polar auxin transport. Analysis by using membrane selective dye FM4-64 and vesicle trafficking inhibitor, BFA reveals that vesicle trafficking is decelerated in pip5k2. Recovery of vesicle trafficking by exogenous PtdIns(4,5)P2 highlights the importance of PtdIns(4,5)P2. PIN2, a well-characterized auxin efflux facilitator, mediates basipetal auxin transport and is crucial for gravitropic response. PIN2 cycling between the plasma membrane and endosomal compartments depends on the clathrin machinery and vesicle trafficking. Decelerated PIN2 recycling and suppressed auxin redistribution in root tip under gravistimulation was observed under pip5k2 background which suggests a critical role of PIP5K2 in root gravity response through regulating PIN2 cycling and polar auxin transport.Keywords Arabidopsis thaliana Phosphatidylinositol monophosphate 5-kinase 2Polar auxin transportVesicle trafficking