Development Of Rnai Gene Silencing System For Disease Resistance Genes In Rice

The vast majority of disease resistance genes cloned from plant genomes encode nucleotide bing site and leucine-rich repeat (NBS-LRR) domains. The goal of this study is to develop a method for fast cloning of resistance genes in rice. First, we analyzed and re-annotated the NBS-LRR encoding genes in the genomes of rice cultivars Nipponbare and93-11. They were classified into771sub-families based on minimum nucleotide identity of85%between two members. The evolution of each sub-family was studied in detail and11sub-families were found to have evolutionary patterns of Type â…  genes, which are extensive chimeras. The evolutionary patterns of Type-â…  and Type-â…¡ resistance genes were confirmed through analysis of corresponding sequences amplified and sequenced from other rice cultivars and wild rice genotypes. Forty-five sub-families were chosen to construct their RNAi silencing lines. First, RNAi vectors were constructed for each sub-family, and were transferred into rice using Agrobacteriun-mediated transformation. Silencing effects of transgenic plants was estimated using RT-PCR. The silencing lines can be used to cross with resistant rice genotypes. If the F1hybrids lose the corresponding resistance, a candicate gene can be identified rapidly. The silencing lines will be useful for future cloning of disease resistance genes in rice.