Abstract
Many spotted-leaf mutants show enhanced disease resistance to multiple pathogen attacks; however, the mechanisms are largely unknown. Here, we reported a novel semi-dominant spotted-leaf mutant 24 (spl24) obtained from an ethyl methane sulfonate (EMS)-induced IR64 mutant bank. spl24 developed tiny brown lesions on the leaf tip and spread down gradually to the leaf base as well as the sheath at the early heading stage. The performances of major agronomic traits such as the plant height, panicle length, number of panicles/plant, and 1000-grain weight were significantly altered in spl24 when compared to the wild-type IR64. Furthermore, spl24 exhibited a premature senescing phenotype with degeneration of nuclear acids, significantly reduced soluble protein content, increased level of malonaldehyde (MDA), and lowered activities of reactive oxygen species (ROS) scavenging enzymes. Disease evaluation indicated that spl24 showed enhanced resistance to multiple races of Xanthomonas oryzae pv. oryzae, the causal pathogen of bacterial leaf blight in rice, with elevated expression of pathogenesis-related genes, salicylic acid (SA) signaling pathway-associated genes revealed by real-time quantitative PCR and high-throughput RNA sequencing analysis. Genetic analysis and gene mapping indicated that the lesion mimic phenotype was controlled by a novel semi-dominant nuclear gene. The mutation, tentatively termed as OsSPL24, was in a 110 kb region flanked by markers Indel-33 and Indel-12 in chromosome 11. Together, our data suggest that spl24 is a novel lesion mimic mutant with enhanced innate immunity and would facilitate the isolation and functional characterization of the target gene.
Highlights
Rice (Oryza sativa L.) is the major staple food for more than half of the world’s population
These products can be classified into three categories: The first group is proteins, such as pathogenesis-related proteins involved in salicylic acid (SA) signaling pathway [9,10], CC-NB-LRR proteins responsible for innate immunity [11], eukaryotic release factor [12], eukaryotic translation elongation factor [13], RNA splicing factor [14,15], membrane-associated proteins [16,17], ion channel regulators [18] as well as clathrin-associated protein [19]
Our results demonstrated that spl24 is a novel spotted-leaf mutant with enhanced disease resistance to multiple races of Xanthomonas oryzae pv. oryzae (Xoo) probably by activating the SA signaling pathway
Summary
Rice (Oryza sativa L.) is the major staple food for more than half of the world’s population. More than 80 rice spotted-leaf mutants have been identified genetically [1,2], most of these mutants are controlled by a single recessive gene, while a few of them are governed by a dominant/semi-dominant gene or double genes Among these mutants, spl generates red-brown lesions without detectable cell death probably due to the accumulation of unknown pigments [3]. We compared the major agronomic traits, analyzed the histochemical indicators of PCD, measured the levels of chlorophylls, soluble proteins and phytohormones, evaluated the disease reaction to Xoo, conducted the expression analysis of defense-related genes, and determined the genetic control of the spotted-leaf phenotype. Our results demonstrated that spl is a novel spotted-leaf mutant with enhanced disease resistance to multiple races of Xoo probably by activating the SA signaling pathway. The data obtained in the present study would facilitate the map-based cloning of OsSPL24 and functional analysis of the mutation underlying the formation of lesions
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