Arabidopsis TAF15b Localizes to RNA Processing Bodies and Contributes to snc1-Mediated Autoimmunity

In both animals and plants, messenger (m)RNA export has been shown to contribute to immune response regulation. The Arabidopsis nuclear protein MOS11, along with the nucleoporins MOS3/Nup96/SAR3 and Nup160/SAR1 are components of the mRNA export machinery and contribute to immunity mediated by nucleotide binding leucine-rich repeat immune receptors (NLR). The human MOS11 ortholog CIP29 is part of a small protein complex with three additional members: the RNA helicase DDX39, ALY, and TAF15b. We systematically assessed the biological roles of the Arabidopsis homologs of these proteins in toll interleukin 1 receptor-type NLR (TNL)-mediated immunity using reverse genetics. Although mutations in ALY and DDX39 did not result in obvious defects, taf15b mutation partially suppressed the autoimmune phenotypes of a gain-of-function TNL mutant, snc1. An additive effect on snc1 suppression was observed in mos11-1 taf15b snc1 triple mutant plants, suggesting that MOS11 and TAF15b have independent functions. TAF15b-GFP fusion protein, which fully complemented taf15b mutant phenotypes, localized to nuclei similarly to MOS11. However, it was also targeted to cytosolic granules identified as processing bodies. In addition, we observed no change in SNC1 mRNA levels, whereas less SNC1 protein accumulated in taf15b mutant, suggesting that TAF15b contributes to SNC1 homeostasis through posttranscriptional mechanisms. In summary, this study highlights the importance of posttranscriptional RNA processing mediated by TAF15b in the regulation of TNL-mediated immunity.