| Plant immune receptors encoded by Resistance (R) genes play essential roles in defense against pathogens, snc1 (suppressor of nprl-1, constitutive 1) is a gain-of-function mutant carrying a mutation in a Toll/interleukin-1 receptor-Nucleotide Binding-Leucine Rich Repeat (TIR-NB-LRR) R protein, sncl constitutively expresses PR] and PR2, accumulates high level of Salicylic Acid (SA) and constitutively activates resistance to pathogen. Multiple R genes, including SNC1 and RPS4, are alternatively spliced, but how plants regulate the splicing of these R genes remains unclear.Here we report the identification of mos14(modifier of sncl-1,14), a mutant that suppresses the immune responses conditioned by the auto-activated Resistance (R) protein sncl. Map-based cloning and complementary analysis showed a G-A mutation in the junction between the 13th exon and the 13th intron of At5g62600 was responsible for the suppression of sncl. At5g62600 encodes a protein with high similarity to previously characterized TRN-SR proteins in animals. Transportin-SR (TRN-SR) is a member of the importin-beta super-family that functions as the nuclear import receptor for serine-arginine rich (SR) proteins, which play diverse roles in RNA metabolism. Confocal microscopy analysis showed MOS14 localized in nucleus. Yeast two-hybrid assays showed that MOS14 interacts with AtRANl via its N-terminus and SR proteins via its C-terminus. In mos14-1, localization of several SR proteins to the nucleus was impaired and alternative splicing patterns of several genes were altered, confirming that MOS14 functions as a TRN-SR.The mos14-1 mutation results in altered splicing patterns of SNC1 and another R gene RPS4 and compromised resistance mediated by them, suggesting that nuclear import of SR proteins by MOS14 is required for proper RNA splicing of the two R genes and is important for their functions in plant immunity. Besides, MOS14 is also important for basal resistance in Arabidopsis. |
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