Fine Mapping And Fuctional Analysis Of A Lesion Mimic Mutant T₃₉ In Rice（Oryza Sativa L.）

Plant lesion mimic mutants（LLM）refer to plants that exhibit spontaneous cell death spots and the physiological and biochemical parameters are similar to hypersensitive response,even in the absence of pathogen infection.Therefore,LLM is a kind of ideal material for studying the mechanism of programmed cell death and disease resistance in plants.The experimental material in this study was a rice lesion mimic mutant named T₃₉,which was induced by ethyl methyl sulfone（EMS）from japonica variety Zhejing 22（ZJ22）.In previous studies,we have found that the lesion mimic spots of T₃₉mutant was induced by light.It showed broad-spectrum and high resistance to bacterial blight.Genetic analysis revealed that the lesion mimic phenotype of T₃₉ was controlled by a single recessive nuclear gene.To further investigate the genetic background of T₃₉,phenotypic characteristics observation,measurement of phenotypic traits,gene mapping,candidate genes sequencing,bioinformatics analysis,and transcriptome sequencing were used in this experiment.The results are summarized as follows:1.Small and purple spots formed on rice leaf of T₃₉ at seedling stage.The main agronomic traits such as plant height,tiller numbers,panicle length,grain number per panicle,seed setting rate and 1000-grain weight decreased significantly.The contents of chlorophyll a,b and carotenoid in the leaves of different part of T₃₉ decreased significantly.After the dark induction for 5 d,the rate of chlorophyll degradation in the leaves of T₃₉mutants were all slower than those of the wild type.2.The mutation of T₃₉ was preliminarily located at the 6.5 Mb region of chromosome 10by SSR molecular marker.The Mut Map genome resequencing results showed that there were8 SNPs showing the SNP index of 1 in the 6.5 Mb region.Combining SNP annotation and genetic linkage analysis by In Del markers,LOC＿Os10g07978 was regarded as the candidate gene for T₃₉ mutants.c DNA sequencing showed that a mutation（C1357T）does exist at 1357base of LOC＿Os10g07978 in T₃₉,causing an amino acid residue changed from Leu to Phe.3.LOC＿Os10g07978 encodes OsRLR1（Oryza sativa RPM1 like resistance gene 1）which is homologous protein of disease resistance protein RPM1 in Arabidopsis thaliana.OsRLR1belongs to CC-NB-LRR immune receptor protein,the multiple sequences alignment showed that the mutation was located in the ARC2 subdomain.The three-dimensional structural modeling of OsRLR1,showed that L453F in ARC2 is close to LRR domain.L453F mutation may affect the interaction between LRR and ARC2 domain,keeping the protein in a sustained active state.4.Tillering and root development of T₃₉ mutants were inhibited,and the morphological observation showed that the axillary buds of T₃₉ formed normally,but elongated more slowly.Transcriptome sequencing of axillary buds of T₃₉ and ZJ22 identifying 624 differentially expressed genes.KEGG enrichment analysis found that the differentially expressed genes were mainly enriched in porphyrin and chlorophyll metabolism,photosynthesis-antenna protein,starch and sucrose metabolism,suggesting chlorophyll metabolism,photosynthesis,and carbon metabolism of axillary buds in T₃₉undergo complex changes.