Isolation and Sequence Analysis of NBS-type Resistance Gene Analogues in Sweet Potato (Ipomoea batatas (L.) Lam.)

Degenerate primers based on conserved motif (P-loop and GLPL) of the nucleotide binding site (NBS) region from the cloned plant disease resistance genes were used to isolate resistance gene analogues (RGAs) from genomic DNA of the sweet potato (Ipomoea batatas (L.) Lam.) cultivar Qingnong No. 2. The desired bands (~500 bp) were purified from the gel, and then cloned by T/A cloning. After sequencing and analyzing by alignment, 15 RGAs with uninterrupted open reading frames (ORFs) were obtained. Sequence identity among the 15 RGA nucleotide sequences ranged from 41.2% to 99.4%, while the 15 RGAs deduced amino acid sequences showed identity ranged from 20.6% to 100%. The phylogenetic analyses for RGA nucleotide sequences and the deduced amino acids showed that RGAs from sweet potato were divided into two groups, TIR (Drosophila Toll or human interleukin receptor-like) type and nonTIR type. The analysis of RGAs amino acid sequence structures suggested that they contained the domains such as P-loop, Kinase-2, Kinase-3a, and GLPL. These results showed that NBS type RGAs isolated from sweet potato might have the same origin and mechanism of evolution as that in other plants.