Disruption of the mRNA m ⁶ A writer complex triggers autoimmunity in Arabidopsis

Distinguishing self from non-self is crucial to direct immune responses against pathogens. Unmodified RNAs stimulate human innate immunity, but RNA modifications suppress this response. mRNA m ⁶ A modification is essential for Arabidopsis thaliana viability. However, the molecular basis of the impact of mRNA m ⁶ A depletion is poorly understood. Here, we show that disruption of the Arabidopsis mRNA m ⁶ A writer complex triggers autoimmunity. Most gene expression changes in m ⁶ A writer complex vir-1 mutants grown at 17°C are explained by defence gene activation and are suppressed at 27°C, consistent with the frequent temperature sensitivity of Arabidopsis immunity. Accordingly, we found enhanced pathogen resistance and increased premature cell death in vir-1 mutants at 17°C but not 27°C. Global temperature-sensitive mRNA poly(A) tail length changes accompany these phenotypes. Our results demonstrate that autoimmunity is a major phenotype of mRNA m ⁶ A writer complex mutants, with important implications for interpreting the role of this modification. Furthermore, we open the broader question of whether unmodified RNA triggers immune signalling in plants.