Isolation and characterization of resistance and defense gene analogs in cotton (Gossypium barbadense L.)

Plant disease resistance gene (R gene) and defense response gene encode some conserved motifs. In the present work, a PCR strategy was used to clone resistance gene analogs (RGAs) and defense gene analogs (DGAs) from Sea-island cotton variety Hai7124 using oligonucleotide primers based on the nucleotide-binding site (NBS) and serine/threonine kinase (STK) in the R-gene and pathogenesis-related proteins of class 2 (PR2) of defense response gene. 79 NBS sequences, 21 STK sequences and 11 DGAs were cloned from disease-resistance cotton. Phylogenic analysis of 79 NBS-RGAs and NBS-RGAs nucleotide sequences of cotton already deposited in GenBank identified one new sub-cluster. The deduced amino acid sequences of NBS-RGAs and STK-RGAs were divided into two distinct groups respectively: Toll/Interleukin-1 receptor (TIR) group and non-TIR group, A group and B group. The expression of RGAs and DGAs having consecutive open reading frame (OiFIF) was also investigated and it was found that 6 NBS-RGAs and 1 STK-RGA were induced, and 1 DGA was up-regulated by infection of Verticillium dahliae strain VD8. 4 TIR-NBS-RGAs and 4 non-TIRNBS-RGAs were arbitrarily used as probes for Southern-blotting. There existed 2-10 blotted bands. In addition, since three non-TIR-NBS-RGAs have the same hybridization pattern, we conjecture that these three RGAs form a cluster distribution in the genome.