The sHSP22 Heat Shock Protein Requires the ABI1 Protein Phosphatase to Modulate Polar Auxin Transport and Downstream Responses.

The phytohormones abscisic acid (ABA) and indole-3-acetic acid (IAA) response pathways interact synergistically or antagonistically to regulate plant development and environmental adaptation. Here, we show that , a key negative regulator of ABA signaling, is essential for auxin-modulated root development. We performed a microarray analysis using the loss-of-function mutant and Col-0 seedlings treated with IAA. For , an endoplasmic reticulum (ER) small heat shock protein-encoding gene, the induction by IAA was dependent on displayed enhanced sensitivity to ABA in primary root growth. In contrast, overexpression of full-length, but not truncated sHSP22 lacking signal peptide and ER-retention sequences, resulted in decreased ABA sensitivity. Overexpressed (OX) partially rescued the ABA hypersensitivity of In addition, is involved in auxin-regulated hypocotyl elongation at high temperature treatment. also affected accumulation of auxin efflux carrier PIN proteins due to potentiated intracellular trafficking. And lines initiated more lateral roots after auxin application. Our results suggest that sHSP22 regulates auxin response through modulating auxin polar transport, and ABI1-sHSP22 provides a novel module orchestrating ABA and auxin signaling crosstalk in Arabidopsis ().