Rice spotted-leaf mutants are ideal materials to study the molecular mechanism underlying programmed cell death and disease resistance in plants. LOC_Os07g04820 has previously been identified as the candidate gene responsible for the spotted-leaf phenotype in rice Spotted-leaf 26 (Spl26) mutant. Here, we cloned and validated that LOC_Os07g04820 is the locus controlling the spotted-leaf phenotype of Spl26 by reverse functional complementation and CRISPR/Cas9-mediated knockout of the mutant allele. The recessive wild-type spl26 allele (Oryza sativa spotted-leaf 26, Osspl26) is highly conservative in grass species and encodes a putative G-type lectin S-receptor-like serine/threonine protein kinase with 444 amino acid residuals. OsSPL26 localizes to the plasma membrane and can be detected constitutively in roots, stems, leaves, sheaths and panicles. The single base substitution from T to A at position 293 leads to phenylalanine/tyrosine replacement at position 98 in the encoded protein in the mutant and induces excessive accumulation of H₂O₂, leading to oxidative damage to cells, and finally, formation of the spotted-leaf phenotype in Spl26. The formation of lesions not only affects the growth and development of the plants but also activates the defense response and enhances the resistance to the bacterial blight pathogen, Xanthomonas oryzae pv. oryzae. Our results indicate that the gain-of-function by the mutant allele OsSpl26 positively regulates cell death and immunity in rice.

Rice bacterial blight (BB) and bacterial leaf streak (BLS), caused by Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc), respectively, are among the most devastating bacterial diseases threatening global rice production. The interactions between rice and Xanthomonas oryzae are complex and dynamic, involving recognition, attack, defense, and adaptation mechanisms enacted by both the rice host and the pathogens. This review summarizes recent advances in understanding rice–Xanthomonas oryzae interactions, focusing on infection models, pathogenic mechanisms, and immune responses elicited by Xanthomonas oryzae. Special attention is devoted to the roles of transcription activator-like effectors (TALEs) and non-TALE effectors in pathogenicity, the functions of resistance (R) genes in defense, and the interconnected molecular networks of interactions derived from multi-omics approaches. Understanding these interactions is essential for developing effective disease-resistance strategies and creating elite disease-resistant rice varieties.

Our study investigates the genetic mechanisms underlying the spotted leaf phenotype in rice, focusing on the spl43 mutant. This mutant is characterized by persistent reddish-brown leaf spots from the seedling stage to maturity, leading to extensive leaf necrosis. Using map-based cloning, we localized the responsible locus to a 330 Kb region on chromosome 2. We identified LOC_Os02g56000, named OsRPT5A, as the causative gene. A point mutation in OsRPT5A, substituting valine for glutamic acid, was identified as the critical factor for the phenotype. Functional complementation and the generation of CRISPR/Cas9-mediated knockout lines in the IR64 background confirmed the central role of OsRPT5A in controlling this trait. The qPCR results from different parts of the rice plant revealed that OsRPT5A is constitutively expressed across various tissues, with its subcellular localization unaffected by the mutation. Notably, we observed an abnormal accumulation of reactive oxygen species (ROS) in spl43 mutants by examining the physiological indexes of leaves, suggesting a disruption in the ROS system. Complementation studies indicated OsRPT5A’s involvement in ROS homeostasis and catalase activity regulation. Moreover, the spl43 mutant exhibited enhanced resistance to Xanthomonas oryzae pv. oryzae (Xoo), highlighting OsRPT5A’s role in rice pathogen resistance mechanisms. Overall, our results suggest that OsRPT5A plays a critical role in regulating ROS homeostasis and enhancing pathogen resistance in rice.

Since the inception of hybrid rice technology 50 years ago, it has not only substantially increased rice yield per unit area but also expedited the development of high-quality rice varieties. However, the evolutionary characteristics of hybrid rice quality remain unclear. To address this gap, it is imperative to leverage more representative and comprehensive hybrid rice resources to analyze phenotypic variation diversity and its primary genetic basis, thereby offering more efficient guidance for molecular breeding. In this study, we selected 2,618 hybrid rice varieties that have been nationally or provincially approved in China over the past 40 years. We analyzed the ecological and chronological evolution characteristics of eight rice quality-related traits: grain length, grain width, grain length-width ratio, chalky grain ratio, chalkiness degree, alkali spreading value, gel consistency, and amylose content (AC). Additionally, we utilized the 'Rice-Navi' system to evaluate the primary molecular basis underlying this evolution. The results revealed that among the eight traits, the coefficient of variation for chalkiness degree was the highest at 0.88, whereas the lowest value of 0.07 was observed for grain width. Significant correlations were found among these traits. The phenotypic evolution results for six major ecological types-Early-season cultivation of indica in South China, Late-season cultivation of indica in South China, Mid-season cultivation of indica in the upper reaches of the Yangtze River, Early-season cultivation of indica in the middle and lower reaches of the Yangtze River, Mid-season cultivation of indica in the middle and lower reaches of the Yangtze River, and Late-season cultivation of indica in the middle and lower reaches of the Yangtze River-indicated that, except for E4, the quality of rice in the other five major ecological types exhibited a significant chronological improvement trend. This trend was highly correlated with the utilization of major superior alleles. Concurrently, the primary genetic background of hybrid rice quality displayed certain ecological diversity characteristics. Overall, this study elucidated the evolutionary characteristics of appearance quality and cooking and taste quality of hybrid rice in southern China from both ecological and chronological perspectives, providing valuable data support for the efficient molecular improvement of rice quality.