Molecular characterization of HEXOKINASE1 in plant innate immunity

Wu Jing,Donah Mary Macoy,Si On Park,Woe-Yeon Kim,Young Hun Kim,Shahab Uddin,Gyeong Ryul Ryu,Rupak Chakraborty,Joon‑Yung Cha,Min Gab Kim,Duong Thu Van Anh

doi:10.1186/s13765-020-00560-8

Wu Jing, Donah Mary Macoy + Show 9 more

Open Access

https://doi.org/10.1186/s13765-020-00560-8

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Abstract

Hexokinase1 (HXK1) is an Arabidopsis glucose sensor that has a variety of roles during plant growth and devlopment, including during germination, flowering, and senescence. HXK1 also acts as a positive regulator of plant immune responses. Previous research suggested that HXK1 might influence plant immune responses via responses to glucose. Plant immune responses are governed by two main pathways: PAMP-triggered immunity (PTI) and effector-triggered immunity (ETI). PTI involves the recognition of Pathogen-Associated Molecular Patterns (PAMPs) and leads to increased callose formation and accumulation of pathogenesis response (PR) proteins. ETI acts in response to effectors secreted by Gram-negative bacteria. During ETI, the membrane-localized protein RPM1-interacting protein 4 (RIN4) becomes phosphorylated in reponse to interactions with effectors and mediates the downstream response. In this study, the effects of glucose on plant immune responses against infection with Pseudomonas syringae pv. tomato DC3000 and other P. syringae strains were investigated in the presence and absence of HXK1. Infiltration of leaves with glucose prior to infection led to decreases in bacterial populations and reductions in disease symptoms in wild-type Arabidopsis plants, indicating that glucose plays a role in plant immunity. Both PTI and ETI responses were affected. However, these effects were not observed in a hxk1 mutant, indicating that the effects of glucose on plant immune responses were mediated by HXK1-related pathways.

Highlights

Sugar metabolism in plants is a critical and complex process that involves glycolysis, the tricarboxylic acid (TCA) cycle, and pentose phosphate pathways
HXK1 positively enhances plant defenses against pathogen infection To investigate the role of HXK1 in Pathogen-Associated Molecular Patterns (PAMPs)-triggered immunity (PTI) and effectortriggered immunity (ETI), the plant immunity-related functions of HXK1 were evaluated using HXK1 deficient mutants generated in the Arabidopsis Col-0 and Landsberg erecta (Ler) backgrounds
Bacterial populations in the infected hxk1 mutants were higher than in WT, consistent with the observed infection phenotype (Fig. 1b, d). These results indicate that HXK1 might play an important role in plant defense, and that absence of HXK1 might negatively affect plant immunity to bacteria, resulting in more severe disease symptoms

Summary

Introduction

Sugar metabolism in plants is a critical and complex process that involves glycolysis, the tricarboxylic acid (TCA) cycle, and pentose phosphate pathways. Hexokinases (HXK) play key roles in sugar metabolism through phosphorylation of glucose to glucose-6-phosphate. The HXK family contains six members: HXK1, HXK2, HXK3, HKL1, HKL2, and HKL3 [1]. HXK1 is a multifunctional protein that is involved in sugar metabolism and signalling. An Arabidopsis hxk mutant exhibited delayed flowering and senescence as well as smaller leaves and Another HXK family member, HXK2, is involved in plant immunity. Overexpression of HXK2 led to enhanced plant resistance to pathogens and was correlated with elevated H2O2 production and expression of defensive genes [4]. HXK1 and HXK2 share similar features: both proteins have several functions, one of which is sugar-sensing in Arabidopsis [5]

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