Characterization of a Novel Gain-of-Function Spotted-Leaf Mutant with Enhanced Disease Resistance in Rice

We here reported the identification and characterization of a novel gain-of-function spotted-leaf 26 (Spl26) mutant from an ethylmethylsulfone (EMS)-induced rice cultivar IR64. Spl26 displayed reddish- brown lesions that firstly appeared on the leaf tips at the early tillering stage and spread gradually downward to cover the whole leaf blades that wilted subsequently. The lesion development was light- dependent under natural conditions. Spl26 exhibited impaired photosynthetic capacity with decreased chlorophyll content and lowered photosynthetic parameters which ultimately led to the poor performance of agronomic traits. Severe cell death occurred in Spl26 in accompany with increased malonaldehyde level and membrane ion leakage rate, elevated reactive oxygen species (ROS) accumulation, altered ROS scavenging activities, increased DNA fragmentation and decreased soluble protein levels. Defense responses were activated in Spl26 with enhanced resistance to rice bacterial blight, up-regulation of defense response genes and altered endogenous hormone levels. The spotted-leaf phenotype is controlled by a single dominant nuclear gene localized to a 305 kb region between RM5490 and InDel42 on the short arm of chromosome 7. The data suggested that Spl26 is a novel gain-of-function spotted-leaf mutant with enhanced bacterial disease resistance and immunity-associated premature leaf senescence and would provide the basis for cloning of the target gene.

A substitution mutation in OsPELOTA confers bacterial blight resistance by activating the salicylic acid pathway

We previously reported a spotted-leaf mutant pelota（originally termed HM_（47）） in rice displaying arrested growth and enhanced resistance to multiple races of Xanthomonas oryzae pv. oryzae. Here, we report the mapbased cloning of the causal gene OsPELOTA（originally termed spl^（HM47））. We identified a single base substitution from T to A at position 556 in the coding sequence of OsPELOTA, effectively mutating phenylalanine to isoleucine at position 186 in the translated protein sequence. Both functional complementation and over-expression could rescue the spotted-leaf phenotype. OsPELOTA, a paralogue to eukaryotic release factor 1（eRF_1）, shows high sequence similarity to Drosophila Pelota and also localizes to the endoplasmic reticulum and plasma membrane.OsPELOTA is constitutively expressed in roots, leaves,sheaths, stems, and panicles. Elevated levels of salicylic acid and decreased level of jasmonate were detected in the pelota mutant. RNA-seq analysis confirmed that genes responding to salicylic acid were upregulated in the mutant. Our results indicate that the rice PELOTA protein is involved in bacterial leaf blight resistance by activating the salicylic acid metabolic pathway.