Cloning and analysis of NBS-LRR type resistance gene analogues in sweet potato (Ipomoea batatas)

The degenerate primers were designed based on the conservative NBS-LRR motifs among the known disease-resistance genes. A fragment of about 500 bp was amplified from genomic DNA of sweet potato using the specifically designed degenerate primers. After cloning and sequencing, 20 NBS-LRR type of disease-resistance gene analogue (RGAs) in sweet potato were observed. The deduced amino acid sequence of DNA fragment contains the conservative motifs of NBS-LRR type RGAs, such as P-loop, Kinase-2α, Kinase-3α and GLPL domain. These 20 RGAs could be sorted into two subclasses, namely TIR-NBS-LRR type and non-TIR-NBS-LRR type. Compared with the known resistance genes including N, L6 and M, the percentages of homologous amino acid sequence in 10 TIR-NBS-LRR range between 21%-44%. While other 10 non-TIR-NBS-LRR assume 15%-46% homology with the known resistance genes (Prf,RPM1, RPS2, etc.). Consequently the RGAs may further be used as molecular marker for screening the candidate disease-resistance genes in sweet potato.