The Molecular Evolution Of Nrg1and Its Role In Resistance Against TMV In Different Nicotiana Species

The interaction between tobacco mosaic virus (TMV) and the N gene is a classical system for studying plant-pathogen interactions. The N gene, originated from Nicotiana glutinosa, encodes TIR-NBS-LRR domains, and confers resistance to TMV. Using a virus-induced gene-silencing (VIGS) approach, a CC-NBS-LRR encoding gene, N requirement gene](NRG1), was found to be an essential component of the N-mediated resistance anainst TMV. In this study, NRG1homologues from different Solanaceae species were amplified using conserved PCR primers. At the same time, NRG1homologues in the14sequenced genomes were retrieved. The positive selection was calculated for NRG1sequences in Solanaceae and only approximately4%of sites were detected to be under positive selection. The phylogenic tree constructed using amino acid sequences of NRG1is consistent with the phylogeny of their corresponding species. We conclude that the NRG1gene is highly conserved and exhibits evolutionary patterns different from other resistance genes. We also used VIGS approach to study the role of NRG1gene and some genes in the signal transduction pathway in resistance against TMV in different Nicotiana species. After silencing key signal transduction genes RAR1, NDR1, PAD4in N. gossei and RAR1, PAD4, NRG1in N. alata, R protein-mediated resistance was lost. Above result suggests that NRG1is also involved in resistance against TMV in N. alata. We are trying to use RNAi method to silence NRG1in tobacco that resistant to TMV. RT-PCR indicates NRG1was sucessfully silenced in N. repanda and its role in resistance against TMV will be investigated in future study.