ABA regulation of stomatal movement and root growth
Deping Hua, Cun Wang，Junna He, Ying Duan, Zhizhong Gong^*

State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University.
^* Corresponding Author:gongzz@cau.edu.cn

Abstract
Abscisic acid (ABA) promotes the ROS production through plasma membrane-associated NADPH oxidases in ABA signaling. ABA regulates stomatal movement and root growth. We performed genetic screens to identify the mutants that show different responses to ABA. Among them, GHR1 (Guard Cell hydrogen peroxide ReSISTANT1) encodes a receptor-like kinase localized on the plasma membrane in Arabidopsis. The ghr1 mutation impaired ABA and H₂O₂ signaling-activation of S-type anion currents in guard cells. Furthermore, GHR1 physically interacted with, phosphorylated, and activated the S-type anion channel SLAC1 when co-expressed in Xenopus oocytes, and this activation was inhibited by ABI2 but not ABI1. We also provide evidence to show that ABA promotes ROS production from mitochondria as indicated by using a mitochondrial superoxide indicator cpYFP, and abo6 (ABA Overly-Sensitive 6), a mutation regulating the splicing of several genes of complex I in mitochondria, accumulated more ROS in mitochondria. Two dominant negative mutations in abi1-1 and abi2-1 greatly reduced the ROS production in mitochondria. The overproduction of ROS affects the auxin signaling and homeostasis and retards root growth. Hence, our results provide novel molecular evidence for the interplay between ABA and auxin through the production of ROS from mitochondria.

Key words: ABA, GHR1, Stomata, Root growth, ABO