A Novel Allele Encoding 7-Hydroxymethyl Chlorophyll a Reductase Confers Bacterial Blight Resistance in Rice.

Marie Gorette Kampire,Bello Babatunde Kazeem,Huimei Wang,Ringki Kuinamei Sanglou,Xiaobo Zhang,Jian-Li Wu

doi:10.3390/ijms22147585

Abstract

Rice spotted leaf mutants are helpful to investigate programmed cell death (PCD) and defense response pathways in plants. Using a map-based cloning strategy, we characterized novel rice spotted leaf mutation splHM143 that encodes a 7-hydroxymethyl chlorophyll a reductase (OsHCAR). The wild-type (WT) allele could rescue the mutant phenotype, as evidenced by complementation analysis. OsHCAR was constitutively expressed at all rice tissues tested and its expression products localized to chloroplasts. The mutant exhibited PCD and leaf senescence with increased H2O2 (hydrogen peroxide) accumulation, increased of ROS (reactive oxygen species) scavenging enzymes activities and TUNEL (terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling) -positive nuclei, upregulation of PCD related genes, decreased chlorophyll (Chl) contents, downregulation of photosynthesis-related genes, and upregulation of senescence-associated genes. Besides, the mutant exhibited enhanced bacterial blight resistance with significant upregulation of defense response genes. Knockout lines of OsHCAR exhibited spotted leaf phenotype, cell death, leaf senescence, and showed increased resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) coupled with upregulation of five pathogenesis-related marker genes. The overexpression of OsHCAR resulted in increased susceptibility to Xoo with decreased expression of pathogenesis-related marker genes. Altogether, our findings revealed that OsHCAR is involved in regulating cell death and defense response against bacterial blight pathogen in rice.

Highlights

Rice bacterial blight is a deadly bacterial disease which is among the most destructive for cultivated rice (Oryza sativa)
A previous study denoted that cell death occurred at every site of necrotic lesions, A previous denoted that cell death occurred at every of necrotic lesions, followed by the study cumulation of hydrogen peroxide in HM143
Our results demonstrated that HM143 triggers the programmed cell death (PCD) pathway, which led to the formation of hypersensitive response (HR)-like necrotic lesions

Summary

Introduction

Rice bacterial blight is a deadly bacterial disease which is among the most destructive for cultivated rice (Oryza sativa). Spotted leaf mutants of rice known to provide extensive resistance to different bacterial pathogens serve as a great material to elucidate disease resistance mechanisms in rice. Understanding the functions of disease-resistant genes is essential for unraveling the molecular mechanisms of plant capacity to withstand pathogenic bacteria and improve plant adaptability to stress through genetic programming [1]. In rice, spotted leaf mutants are known to develop necrotic lesions spontaneously without any environmental stress intervention. The developed necrotic lesions are mainly observed on the leaf blade or leaf sheath and are of different sizes (2–10 μm) and multiple colors such as brown, reddish-brown, dark brown, orange, and white [2,3]. Spotted leaf mutants are termed lesion mimic mutants (LMMs) because they display either structural or uncontrolled cell death initiation similar to the hypersensitive response (HR) induced by pathogen infection [4]. HR is associated with typical physiological processes that comprise structural signals such as the initiation of pathogenesis-related (PR) genes, the outburst of ROS, the aggregation of antimicrobial compounds, and the generation of free radicals [5,6,7]

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Results

Conclusion