Orchestration of Processing Body Dynamics and mRNA Decay in Arabidopsis Immunity

Summary: Proper transcriptome reprogramming is critical for hosts to launch an effective defense response upon pathogen attack. How immune-related genes are regulated at the posttranscriptional level remains elusive. We demonstrate here that P-bodies, the non-membranous cytoplasmic ribonucleoprotein foci related to 5′-to-3′ mRNA decay, are dynamically modulated in plant immunity triggered by microbe-associated molecular patterns (MAMPs). The DCP1-DCP2 mRNA decapping complex, a hallmark of P-bodies, positively regulates plant MAMP-triggered responses and immunity against pathogenic bacteria. MAMP-activated MAP kinases directly phosphorylate DCP1 at the serine237 residue, which further stimulates its interaction with XRN4, an exonuclease executing 5′-to-3′ degradation of decapped mRNA. Consequently, MAMP treatment potentiates DCP1-dependent mRNA decay on a specific group of MAMP-downregulated genes. Thus, the conserved 5′-to-3′ mRNA decay elicited by the MAMP-activated MAP kinase cascade is an integral part of plant immunity. This mechanism ensures a rapid posttranscriptional downregulation of certain immune-related genes that may otherwise negatively impact immunity. : Yu et al. show that P-body core components DCP1 and DCP2 positively regulate plant pattern-triggered immunity. DCP1 phosphorylation by immune-activated MAPKs contributes to P-body disassembly and mRNA decay on a subset of immune-regulated genes, revealing mRNA-decay-mediated posttranscriptional regulation is an integral part of plant immunity. Keywords: plant immunity, microbe-associated molecular patterns, processing body, mRNA decay, mRNA decapping complex, MAP kinases