Analysis Of NBS Gene Family Based On Gonome-wide Resequencing In JG21 And Its Parent

Jingu21, generated from Jinfen52 by radiating dry seeds with cobalt 60 gamma-ray and selective breeding, is a high-quality millet variety. However, it is prone to diseases such as downy mildew, millet biast and smut seriously, affecting its yield and quality. Nucleotide binding site (NBS) resistance genes are the largest class in plant disease resistance gene families, and it has become the focus of research for breeding new varieties with disease resistance. In this study, we investigated the difference between Jingu21 and Jinfen52 on genome-wide level based on whole-genome resequencing with Yugul as the reference genome, and explored the potential factors related to the disease susceptibility of Jingu21. This study would provide a theoretical basis for further research on the disease resistance in foxtail millet. The results are as the followings:1.Genome-wide identification and phylogenetic analysis of NBS gene family in foxtail millet showed that: (1) The mapping rate and coverage rate are high for both genome-resequencing of Jingu21 and Jinfen52, and single nucleotide mutation was the major variation type between the two varieties.(2) There were 285 and 282 NBS genes in Jingu21 and Jinfen52, respectively, as identified by searching the reference genome with key words-disease resistance and then blasting the genomes of these two varieties. They were mostly located on chromosome 8, followed by chromosome 9 and chromosome 5.(3) Several different branches of phylogenetic tree for NBS genes were observed, and the number of NBS genes in each branch was different, indicating that these genes did not have a separate evolutionary pattern and the evolution of resistance genes was more complex than expected.2.Analysis of the identified NBS genes by comparing the SNPs, InDels, SVs showed that:(1) The length of chromosome 8 was not the longest, but the variation type and number of that was the greatest.(2) Among the confirmed three genes showed difference between Jingu21 and Jinfen52, Si027260 is absent in Jinfen52, might be related to the resistance difference between these two varieties.3.Si028867 and Si028867 genes in Jingu21 and Jinfen52 were cloned and their sequences and protein structures were analysed, which showed that:(1) Si028867 gene had five single base mutations, and Si033294 gene had one single base mutation and one insertion between the two foxtail millet varieties.(2) One of the mutations of Si028867 was synonymous mutation. The insertion of Si033294 caused a great difference in the amino acid sequences between Jinggu21 and Jinfen52.(3) Secondary and tertiary structure of Si028867 protein had no significant differences, whereas that of Si033294 protein showed significant differences between the two foxtail millet varieties. Si033294 in Jinfen52 was a hydrophilic protein, and the secondary structure of the protein was random coil structure; whereas in Jingu21, Si033294 was a hydrophobic protein, and its secondary structure was mainly composed of ?-helix.(4) Aligment analysis of Si028867 and Si033294 showed that these two proteins were highly similar with their homologous proteins in other gramineae. Phylogenetic analysis showed that the deduced amino acid sequence of Si028867 was most similar to that of maize and the deduced amino acid sequence of Si033294 was most similar to that of sorghum.In summary, the main mutation type among NBS genes in Jingu21 and Jinfen52 was the single nucleotide mutation. The disease susceptibility of Jingu21 may be due to base mutations, and may also be caused by the presence Si027260. This article provides a wealth of genomic information and theoretical foundation for the further exploration of the disease susceptibility of high-quality variety Jingu 21 and the NBS genes in foxtail millet.