Isolation and identification of two genes encoding leucine-rich repeat (LRR) proteins differentially responsive to pathogen attack and salt stress in tobacco

Leucine-rich repeat proteins (LRRs) play important roles in signal perception and activation of defense responses. We isolated two new LRR genes, NtLRR1 and NtLRR2, in tobacco (Nicotiana tabacum). NtLRR1 and NtLRR2 are characterized by 9 and 3 LRR domains, respectively. The phylogenetic relationships show that NtLRR1 and NtLRR2 belong to different subfamilies of the polygalacturonase inhibitor proteins (PGIPs) and LRP-related proteins (LRPs), respectively. NtLRR1 and NtLRR2 are responsive to pathogen attack and salt stress, but display differential expression patterns in tobacco. NtLRR1 is activated rapidly by infection with the tobacco wildfire pathogen (Pseudomonas syringae pv. tabaci), but slowly by tobacco mosaic virus (TMV). In contrast, NtLRR2 transcripts rapidly accumulate after infection with TMV, and only sluggishly with infection by the wildfire pathogen. In addition, NtLRR1 transcripts abundantly accumulate in stems, whereas NtLRR2 appears mainly in the roots. Isolation of the NtLRR2 promoter revealed some cis-acting elements responding to stresses and defense signal molecules. Subcellular localization indicated that NtLRR1 and NtLRR2 proteins localize in the cell walls and plasma membranes, respectively. It was concluded that NtLRR1 and NtLRR2 are important proteins having different functions in response to different stresses and mediating in binding interactions in a wide variety of biological processes.