Characteristics And Gene Mapping Of Two Lesion Mimic Mutant In Soybean

Plant lesion mimic refer to the phenotype of necrosis or pathogen-infection in plants due to mutations of their own genes in the absence of infection by outside pathogens.Plant lesions mimic are one of the hotspots in plant research,and are of great significance for understanding the mechanisms of plant cell apoptosis,defense response,and growth and development.As an important food and economic crop,soybean（Glycine max（L.）Merr.）studies the mechanism of its lesion mimic mutants and excavating genes related to its defense pathways,which is conducive to providing excellent genetic resources for soybean breeding.Previously,the National Center for Soybean Improvement mutagenized the lesion mimic and rugose leaf mutant abl_CT created by Naivong CT-2 through 60CO radiation,and its leaf traits resemble viral infections;another lesion mimic and presenility mutant N86-4y was obtained by EMS mutagenesis of the cultivated soybean Nannong 86-4,its mature leaves have yellowed edges and presenility and dwarfing,resemble the symptoms of some fungal infections that harm soybean.In the study,we want to evaluate morphological and physiological characteristics of the two target traits then to reveal their inheritance and to map and identify target genes.This result would provide a reference for the in-depth study of the molecular mechanism of the formation of soybean lesion mimic mutants,revealing the mechanism of soybean defense pathways,and excavating specific gene resources.The main results are as follows:1.Morphological and physiological characteristics of two soybean mutants traits.There is no difference between the lesion mimic and rugose leaf mutant abl_CT and the wild type at the seedling stage,and the obvious lesion mimic phenotype appears after the fifth pair of compound leaves were deployed.The photosynthetic pigment content of the mutant is not significantly different from that of the wild type,but the net photosynthetic rate is significantly lower than that of the wild type.It is speculated that the thickening of the leaf palisade and sponge tissue of the mutant is the main reason for the decrease in net photosynthetic rate.The trait values of plant height and yield components of abl_CT were all lower than those of the wild type,the number of pods per plant and the number of seeds per plant were only 3.8%and 3.2%of the wild type.For the second lesion mimic mutant N864y,compared with the wild type,The lesion mimic phenotype began to develop from the fifth pair of compound leaves,and the mutant died during flowering.And the photosynthetic pigment content and net photosynthetic rate of N86-4y were significantly lower than those of wild type.The investigation of agronomic traits revealed that the leaf area and plant height of N86-4y were smaller than that of wild type.2.Inheritance,gene mapping and candidate genes analysis for soybean lesion mimic mutant abl_CT.The F1 generation derived from the cross between abl_CT and 2 normal parents showed normal parental morphology,indicating that the lesion mimic and rugose leaf traits were controlled by recessive genes;further based on the separation of the F2 and F3 generation traits,it was inferred that the trait was controlled by a single recessive gene,named as rI3.The target genes were further mapped on chromosome 2 between SSR markers Sat₁39 and BARCSOYSSR₀2₁453 using two recessive individuals of the combined F2 population.The physical distance of the region is 325Kb,containing 34 predicted genes.Sequence analysis of the genes in the region showed that the 4372th base in the seventh exon of Glyma.02g233500 was replaced from T to C,and the amino acid was replaced from methionine（Met）to threonine（Thr）.This gene encodes tRNA pseudouridine synthase and plays an important role in RNA modification.It is speculated that this gene is the target gene.Predicting the protein structure of the gene,it was found that the mutant protein secondary and tertiary structure have changed.3.Inheritance and gene mapping of traits of soybean lesion mimic and presenility mutant N86-4y.According to the trait segregation of the F1-F2:3 generations of the W82×N86-4y crosses,it was found that the mutant phenotype was controlled by single recessive genes designated as ylp.Using the F2 recessive individuals of W82×N86-4y cross,the target gene ylp was mapped between the SSR markers BARCSOYSSR₁9₁583 and the end of the chromosome on the chromosome 19,The physical distance of the region is 527Kb,containing 68 predicted genes.According to previous studies,seven genes that may be related to lesion mimic were found in the candidate segment,they are Glyma.19G257500,Glyma.19G257700,Glyma.19G258700,Glyma.19G260300,Glyma.1 9G261000,Glyma.19G261700 and Glyma.19G263300.