Deciphering The Evolution Of NBS-LRR Genes In Eurosids ? And Allele Mining Of Rice Blast Resistance Genes

The vulnerable effects of diverse spectrum of pathogens have led to determine the specificity of plant immune system conferring disease resistance(R)genes.It has been reflected that R proteins guard against the pathogens which overcame the first layer PAMP bringing the effectors into action.Hence,the remarkable R-genes present in multigene clusters coincide with true alleles across naturally occurring speciation.This continuous co-evolutionary struggle interacting with pathogens have provided great insights in molecular studies of plant immunity,integrating a picture of plant-pathogen interaction reliable for enhancing resistance in crops against diseases.From many decades different evolutionary studies of the largest class of disease resistance genes consisting of a nucleotide binding site(NBS)and leucine-rich repeats(LRRs)have been discovered in many species.Presently,in our study the systemic research of NBS-encoding genes in Eurosids ? species have been explored.The research of five Eurosids ? species via Gossypium raimondii,Theobroma cacao,Carica papaya,Citrus clementina,and Arabidopsis thaliana has revealed great insights into the evolutionary patterns of the NBS-encoding genes with frequent copy number variations.Phylogenetic tree analysis and the numbers of the NBS-encoding genes in the common ancestor of these species elucidated species-specific NBS clades,including multi-copy and single copy numbers which interpreted dominant among these genes.Rapid turn-over with birth and death rate of the NBS-encoding genes among Eurosids ? species was explored.In addition,a strong positive correlation was observed between the TIR type NBS-encoding genes and species-specific genes,indicating rapid gene loss and duplication.The polymorphism of R genes is an important source of resistance specificity creating diversity.The allelic variants influencing different haplotypes provide a structural reservoir for evolutionary forces to generate rapid variation in resistance specificity.Through allele mining strategy variations can be explored through candidate genes which help to identify novel alleles of gene of interest from a wide range of germplasm.In this present study,we explored the genetic variability of resistance genes conferring natural evolution,based on the prediction of functional candidate resistance genes using allele mining method.We elaborated the genetic diversity and allelic variations among 47 previously identified resistance gene loci and cloned them from 8 indica rice varieties.We finally got 89 clones from different varieties.All cloned genes were sequenced and transferred into the susceptible rice cultivars.The transformants with enough seeds were screened to evaluate the resistance by 16 independent rice blast strains selected from different parts of China.We got 25 resistant transgenic lines,which contained 14 gene loci.Despite to the high proportion of resistance genes,few or only one gene is resistant to 9 of all the strains.Most resistance genes conferred resistance to a limit number of rice blast isolates.Our results suggest that multiple alleles with continuous recombination,thereby generate and maintain polymorphism,and produce new functional genes.