The Arabidopsis deNADding Enzyme DXO1 Modulates the Plant Immunity Response

DXO1, the only DXO homolog in Arabidopsis, due to its plant-specific features, exhibits strong deNADding enzymatic activity but has no apparent role in 5' QC. Despite its important contribution to plant RNA metabolism, the direct impact of DXO1 enzymatic activity on cellular processes appears surprisingly limited. Notably, most molecular and morphological changes observed so far in dxo1 mutant plants depended on the plant-specific N-terminal domain of the protein. Our investigation into the role of DXO1 in response to biotic stress, specifically its susceptibility to Pseudomonas syringae pv. tomato DC3000 infection, unexpectedly revealed the importance of DXO1 enzymatic activity in the plant immune response. We observed that dxo1-2 knockout mutant and transgenic dxo1-2 lines expressing a DXO1 variant either catalytically inactive or lacking the N-terminal domain exhibited enhanced resistance to Pst, accompanied by marked changes in the expression of key pathogenesis markers. Also, other markers of plant immunity, such as callose deposition and production of reactive oxygen species, were strongly induced by PAMPs elf18 and flg22. These results strongly suggest that both DXO1 features, the N-terminal domain and its catalytic site, contribute to the regulation of plant immunity. This is the first observation revealing the involvement of DXO1 enzymatic activity in plant physiology. Moreover, our analyses showed that dxo1-2 mutation altered the expression of a large group of defense-related genes, affected the stability of mRNAs, and delayed the activation of MAP kinases. Therefore, we postulate that DXO1 protein deregulates defense against Pst infection at both the transcriptional and posttranscriptional levels.