Genome-Wide Analysis of Nucleotide-Binding Site (NBS) Disease Resistance (R) Genes in Sacred Lotus (Nelumbo nucifera Gaertn.) Reveals Their Transition Role During Early Evolution of Land Plants

Nucleotide-binding site (NBS) containing genes comprise the largest class in identified plant resistance genes. A total of 137 NBS class resistance genes were identified from the newly sequenced sacred lotus genome (Nelumbo nucifera Gaertn.) through a reiterative computational sequence analysis. Three distinct groups of NBS-encoding genes were classified: 5 with Toll/interleukin-1 receptor homology (TIR) domain at N-terminal (TIR-NBS [-LRR (leucine-rich repeat)]), 37 with CC (coiled coil) domain (CC-NBS [-LRR]), and 95 with neither TIR nor CC at N-terminal (NBS [-LRR]). Sequence analysis revealed high divergence of NBS-LRR genes in sacred lotus. The result of cluster and syntenic analysis of NBS genes suggested a duplication and recombination event, which is consistent with the correspondent result of whole genome analysis. In addition, we also identified 52 NBS genes which have a putative NACHT domain embedded in the NBS domains. This characteristic has only been reported in animals, fungi and bacteria, suggesting that NACHT and NBS domains shared a similar ancient origin; and sacred lotus NBS (NACHT) genes may represent a transition role during the early evolution of disease resistance in land plants.