NMD-mediated posttranscriptional regulation fine-tunes the NLR-WRKY regulatory module to modulate bacterial defense response

Nonsense-mediated mRNA decay (NMD) is a conserved eukaryotic surveillance system that maintains transcriptome integrity by degrading aberrant RNA transcripts. NMD ensures proper growth and development by preventing autoimmunity through the direct regulation of nucleotide-binding, leucine-rich repeat (NLR) genes. Whether NMD directly regulates WRKY genes remains unclear, despite their upregulation in NMD-deficient plants, and potential feedback between NLRs and WRKYs is also poorly understood. In this study, we showed that NMD also directly regulates a subset of WRKY (WRKY15, 18, 25, 33, 46, 60, and 70) genes, particularly at lower temperatures (16°C). NMD signature-containing transcripts of WRKY46 and WRKY70, selected as representative NMD-regulated WRKY genes, showed increased half-lives in NMD-deficient mutants. Transcriptome analyses showed that these seven NMD-regulated WRKY genes are induced in response to bacterial infection. Potential homologues of these seven NMD-regulated WRKY genes in maize and rice showed similar induction in response to bacterial pathogen infection. Furthermore, these NMD-regulated WRKY genes are induced in plants overexpressing RESISTANT TO P. SYRINGAE 4 (RPS4) in a temperature-dependent manner. By using ChIP-seq and DAP-seq data of WRKY transcription factors, we showed that WRKYs potentially regulate a significant number of NLR genes by directly binding to the W-box in their promoter regions. Taken together, our findings revealed that in addition to the NLRs, the NMD machinery also regulates WRKY genes to keep the basal defense levels in check and the WRKY transcription factors directly regulate NLR genes to constitutes a positive feedback regulatory loop to optimize the plant response to invading pathogens.