DDX6-like RNA helicases compromise salt-stress tolerance by facilitating mRNA decapping activity in Arabidopsis

RNA helicases are a large family of ATPases that participate in RNA structure remodeling and ribonucleoprotein rearrangement to regulate plant growth, development, and responses to environmental stress. Here, we observed that the expression of Arabidopsis (Arabidopsis thaliana) DDX6-like RNA helicase genes RH6, RH8, and RH12 was down-regulated by salt stress. Loss-of-function mutants showed enhanced salt-stress tolerance, manifested as precocious seed germination, accelerated growth, less oxidative stress, and reduced Na+ accumulation compared with wild-type plants. Conversely, overexpression of RH6 led to salt hypersensitivity. Transcriptome analysis further revealed that DDX6-like RNA helicases destabilize the transcripts of numerous salt stress responsive genes. A modified 5'-RNA ligase mediated rapid amplification of cDNA ends (5'-RLM-RACE) assay indicated that this destabilization can likely be attributed to enhanced decapping activity under NaCl treatment. Lack of DDX6-like RNA helicases attenuated P-body formation under saline conditions. We conclude that DDX6-like RNA helicases negatively regulate the salt-stress response by modulating 5'-3' decay of salt-related mRNA transcripts.