Cloning and Analysis of Resistance Gene Analogs in Litchi

Degenerate oligonucleotide primers based on conserved motifs in the NBS region of known resistance proteins were used to amplify sequences from genomic DNA of Litchi ( Lichi chinensis Sonn.) by polymerase chain reaction (PCR). A bright band of about 500bp was acquired. After cloning, 5 classes of clones were selected for sequencing. Searching in the GeneBank database using BLAST revealed that all 5 sequences shared various degrees of amino acid identity with several cloned NBS LRR class plant disease resistance genes and many RGAs from other plant species. When the sequences of each class were compared with known resistance gene sequences, the percentage of amino acid identity ranged from 13 5% ～ 45 9%. These RGAs can further be used as probes for resistance gene cloning and construction of genetic map in Litchi. The results indicate that PCR-based approaches using degenerate primers based on the conserved NBS domains of known resistance genes could be a potentially useful strategy for isolating resistance genes in fruit trees.