Evolution of plant NBS encoding disease resistance genes.

NBS (nucleotide-binding site) genes are a major class of disease resistance (R) genes in plants. Studies on their evolutionary pattern, structure characteristics and functional regulation have been always paid much attentions. NBS genes exist in a various plants by different copy numbers and low expression levels. They encode proteins containing conserved NBS domain and C-terminal leucine-rich repeats (LRRs). The NBS genes have frequent sequence exchanges among homologs and consequently show extensive diversity and poor synteny. Two types of NBS genes are distinguished based on their frequency of sequence exchanges. In this review, we summarize the latest progress of plant NBS encoding genes in terms of structure, number, evolutionary pattern, sequence diversity and distribution in genome, providing some insights into the further research on NBS genes in plant.