Isolation, characterization and sequence analysis of resistance gene analogs (RGAs) in plants related to Huanglongbing(HLB)

Abstract

Citrus production is seriously affected by HLB to which no resistant plant is available in the cultivated germplasm. Degenerate primers designed based on conserved NBS (nucleotide binding site) motifs contained in some plant resistance genes were used to isolate analogous sequences called resistance gene analogs (RGAs). About xx resistance gene analogs (RGAs) were cloned from several spices related to HLB using PCR method with primers above-mentioned. The BLASTN searches revealed that 43 DNA fragments showed different sequence homology with known plant R-genes or deposited RGAs and 12 sequences could be translated to polypeptides without stop codons. These RGAs and 12 deduced amino acid were analyzed by Clustalx and DNAMAN software. Sequence analysis showed these RGAs contain the conserved domains P-loop, Kinase-2a, Kinase-3a, and HD, which was conserved in NBS-LRR type disease resistance gene. These 12 RGAs shared 37.39%-43.43% identity with the resistance genes of TobaccoN, FlaxL6, Arabidopsis thaliana RPS2, RPS5, RPP8, RPM1. Gene duplication followed by sequence divergence were proposed as the mode for the evolution of a large number of distantly or closely related RGA genes in plants, and this mode may play a role in the generation of new resistance specificity and cloning related resistance genes about HLB. © 2012 Springer-Verlag GmbH.