A role for two-component signaling elements in the Arabidopsis growth recovery response to ethylene.

Brad M Binder,Dennis E Mathews,G Eric Schaller,Claire E Hutchison,Joseph J Kieber,Hyo Jung Kim

doi:10.1002/pld3.58

Abstract

Previous studies indicate that the ability of Arabidopsis seedlings to recover normal growth following an ethylene treatment involves histidine kinase activity of the ethylene receptors. As histidine kinases can function as inputs for a two‐component signaling system, we examined loss‐of‐function mutants involving two‐component signaling elements. We find that mutants of phosphotransfer proteins and type‐B response regulators exhibit a defect in their ethylene growth recovery response similar to that found with the loss‐of‐function ethylene receptor mutant etr1‐7. The ability of two‐component signaling elements to regulate the growth recovery response to ethylene functions independently from their well‐characterized role in cytokinin signaling, based on the analysis of cytokinin receptor mutants as well as following chemical inhibition of cytokinin biosynthesis. Histidine kinase activity of the receptor ETR1 also facilitates growth recovery in the ethylene hypersensitive response, which is characterized by a transient decrease in growth rate when seedlings are treated continuously with a low dose of ethylene; however, this response was found to operate independently of the type‐B response regulators. These results indicate that histidine kinase activity of the ethylene receptor ETR1 performs two independent functions: (a) regulating the growth recovery to ethylene through a two‐component signaling system involving phosphotransfer proteins and type‐B response regulators and (b) regulating the hypersensitive response to ethylene in a type‐B response regulator independent manner.

Highlights

Two-component signaling systems involve histidine kinases, response regulators, and sometimes histidine-containing phosphotransfer proteins (Mizuno, 2005; Schaller, Shiu, & Armitage, 2011)
We examined loss-of-function mutants involving the histidine kinase-linked cytokinin receptors AHK2, AHK3, and AHK4 to determine whether the slow growth recovery phenotype was unique to ethylene receptor mutants (Figure 1)
These results indicate that histidine kinase activity of the ethylene receptor ETHYLENE RESPONSE1 (ETR1) performs two independent functions: (a) regulating the growth recovery to ethylene through a two-component signaling system involving ARABIDOPSIS HISTIDINE-CONTAINING PHOSPHOTRANSMITTERs (AHPs) and type-B ARABIDOPSIS RESPONSE REGULATORs (ARRs) and (b) regulating the hypersensitive response to ethylene in a type-B ARR-independent manner

Summary

| INTRODUCTION

Two-component signaling systems involve histidine kinases, response regulators, and sometimes histidine-containing phosphotransfer proteins (Mizuno, 2005; Schaller, Shiu, & Armitage, 2011). The double mutant etr1-7;ers is delayed in its ability to recover normal growth rate, and this can be rescued by introducing a wild-type version of ETR1 but not by a kinase-inactive version of ETR1 (Binder, O’Malley, et al, 2004) These results suggest that histidine kinase activity and, by extension, the multistep phosphorelay may mediate the ability of seedlings to recover normal growth following cessation of ethylene treatment. We tested this hypothesis by performing a kinetic analysis of the ethylene growth response and recovery in mutants of Arabidopsis twocomponent signaling elements. The potential mechanisms underlying these differences in histidine kinase-mediated regulation are discussed

| MATERIALS AND METHODS

| RESULTS

Findings

| DISCUSSION