Alternatively spliced N resistance gene transcripts: Their possible role in tobacco mosaic virus resistance

The N gene, a member of the Toll-IL-1 homology region-nucleotide binding si te-leucine-rich repeat region (LRR) class of plant resistance genes, encode s two transcripts, N-S and N-L, via alternative splicing of the alternative exon present in the intron III. The N-S transcript, predicted to encode th e full-length N protein containing the Toll-IL-1 homology region, nucleotid e binding site, and LRR, is more prevalent before and for 3 hr after tobacc o mosaic virus (TMV) infection. The N-L transcript, predicted to encode a t runcated N protein (N-tr) lacking 13 of the 14 repeats of the LRR, is more prevalent 4-8 hr after TMV infection. Plants harboring a cDNA-N-S transgene , capable of encoding an N protein but not an N-tr protein, fail to exhibit complete resistance to TMV. Transgenic plants containing a cDNA-N-S-bearin g intron III and containing 3' N-genomic sequences, encoding both N-S and N -L transcripts, exhibit complete resistance to TMV, These results suggest t hat both N transcripts and presumably their encoded protein products are ne cessary to confer complete resistance to TMV.