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

• Main Authors: Marie Gorette Kampire, Ringki Kuinamei Sanglou, Huimei Wang, Bello Babatunde Kazeem, Jian-li Wu, Xiaobo Zhang
• Format: Article
• Language: English
• Published: MDPI AG 2021-07-01
• Series: International Journal of Molecular Sciences
• Subjects: rice; bacterial blight; defense response; <i>OsHCAR</i>
• Online Access: https://www.mdpi.com/1422-0067/22/14/7585

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 <i>spl^HM143</i> that encodes a 7-hydroxymethyl chlorophyll a reductase (<i>OsHCAR</i>). The wild-type (WT) allele could rescue the mutant phenotype, as evidenced by complementation analysis. <i>OsHCAR</i> 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 <i>OsHCAR</i> exhibited spotted leaf phenotype, cell death, leaf senescence, and showed increased resistance to the bacterial pathogen <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> <i>(Xoo)</i> coupled with upregulation of five pathogenesis-related marker genes. The overexpression of <i>OsHCAR</i> resulted in increased susceptibility to <i>Xoo</i> with decreased expression of pathogenesis-related marker genes. Altogether, our findings revealed that <i>OsHCAR</i> is involved in regulating cell death and defense response against bacterial blight pathogen in rice.