Origin,Diversity and Evolution of NBS-type Disease-resistance Gene Analogues in Sea-island Cotton (Gossypium barbadense L.)

The majority of plant disease resistance genes (R genes) isolated encodes a predicted nucleotide binding site (NBS) domain.The NBS sequences can be divided into two major groups.GroupⅠ of NBS domains contains TIR ( Drosophala Toll or human interleukin receptor like ) and groupⅡ does not.The two groups are all distributed in dicot species.NBS domains related to R genes show a highly conserved backbone of amino acid motifs,which makes it possible to isolate resistance gene analogues (RGAs) by PCR with degenerate primers.Multiple combinations of primers designed from two conserved motifs in the NBS regions of R genes of various plants were used to amplify genomic DNA of sea island cotton,var.Pima 90 ( Gossypium barbadense ),the desired bands were purified from the gel,and then cloned by T/A cloning.After sequenced and analyzed by alignment,31 RGAs were isolated.Among the RGAs,nineteen were uninterrupted open reading frames (ORFs).We have multialigned the 31 RGAs and 34 RGAs of ( Gossypium hirsutum ) germline M 249 by searching in GenBank,they were divided into two classes.ClassⅠ included only upland cotton RGAs,class Ⅱ include all upland cotton and sea island cotton RGAs.Two distinct groups,TIR type and non TIR type,were classified by phylogenetic analysis in sea island cotton.The analysis of the 19 ORFs structures suggested that they contain the motifs such as P loop,Kin 2,“PLAL” and RNBS A,B,C,as defined by Meyers.These indicate that NBS type disease resistance gene analogues in sea island cotton have the common origin and evolution with the other plants.