The Arabidopsis deNADding enzyme DXO1 modulates the plant immunity response

DXO1, the only DXO homolog in Arabidopsis, due to its plant-specific features, has a strong deNADding enzymatic activity but no apparent role in 5′QC. 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 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 Pseudomonas syringae , accompanied by marked changes in the expression of key pathogenesis markers. Other markers of plant immunity, such as callose deposition and production of ROS, were strongly induced by elf18 and flg22.

Our results strongly suggest that both DXO1 features, the N-terminal domain and its catalytic site, contribute to regulating plant immunity. This is the first observation revealing the involvement of the 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 their mRNAs’ stability, and delayed activation of MAP kinases. Therefore, we postulate that DXO1 protein deregulates defense against Pst infection at both the transcriptional and post-transcriptional level.