Blast Resistance Identification And Evolutionary Analysis Of NBS-LRR Genes In Rice

Blast disease is one of the most destructive threat to rice productivity and the global food security while utilizing the abundant resistance genes within the rice genome as breeding resource has been proven to be the most economically effective approach towards it so far.Unfortunately,with the existing resistant varieties being degenerating,there is an urge to develop proper solutions to improve the complicated and time-consuming breeding methods.In the previous study our lab has established a high-throughput cloning system for rice blast genes based on our preliminarily tested assumption that the rapidly evolving R genes must function crucially in the defense against blast caused by constantly evolving pathogen.Derived from this idea we continued to explore the evolution of NBS-LRR genes by focusing on members sharing common genetic features,combining the resistance identification the genetic profile of these NBS-LRR genes was hoped to be revealed.5 members were randomly chosen in the two rapidly evolving NBS-LRR gene families among species while conservative within species,and non-rapidly evolving NBS-LRR genes respectively to carry out cloning and genetic transformation as well as the following blast infection treatment.The identification of resistance showed there were 4 out of 10 genes in the families and 2 out of 5 in the non-rapidly evolving ones conferring resistance against rice blast,among which the resistant Os05g31530 along with the other two members in the same cluster,Os05g31570 and Os05g31550,were selected as the target genes for further study because of high sequence identity.The results showed that these genes had low sequence diversity and were under purifying selection during the domestication of rice.The analysis also supported the idea that for Os05g31530 and Os05g31570 there were not only introgression between cultivated rice and wild rice but frequently-occurred recombination.Specifically,the resistant haplotype was shared by all the populations including Indica,Japonica and their wild relatives,suggesting that through introgression and recombination might this gene gain and maintain its resistance for blast.The obvious introgression detected in Os05g31530 was an indication for its actively participation in natural-happened hybridization or artificial breeding process,which may have something to do with its underlying while conservative function in rice while the constant recombination behind introgression gave it massive accesses to genetic communication which meant a lot to its resistance.This study added another intriguing example to the survey of the rice blast NBS-LRR genes and implied that the possible existence of diversified genetic characteristics as well as disease resistance mechanisms which could be a hint for more comprehensive exploration and deployment of NBS-LRR genes.