Protein phosphorylation, especially serine/threonine and tyrosine phosphorylation, plays significant roles in signalling during plant growth and development as well as plant responses to biotic or abiotic stresses. Dual-specificity protein tyrosine phosphatases dephosphorylate components of these signalling pathways. Here, we report that an atypical dual-specificity protein tyrosine phosphatase, AtPFA-DSP3 (DSP3), negatively affects the response of plants to high-salt conditions. A DSP3 loss-offunction mutant showed reduced sensitivity to salt treatment. DSP3 was primarily localized in nuclei and was degraded during salt treatment. Compared to wild type, the level of ROS was lower in the dsp3 mutant and higher in plants ectopically expressing DSP3, indicating that higher DSP3 level was associated with increased ROS production. DSP3 interacted with and dephosphorylated MPK3 and MPK6.Genetic analyses of a dsp3mpk3 double mutant revealed that DSP3's effect on salt stress depends on MPK3. Moreover, the phosphatase activity of DSP3 was required for its role in salt signalling. These results indicate that DSP3 is a negative regulator of salt responses in Arabidopsis by directly modulating the accumulation of phosphorylated MPK3 and MPK6.

Protein phosphorylation, especially serine/threonine and tyrosine phosphorylation, plays significant roles in signaling processes during plant growth and development as well as their responses to biotic or abiotic stresses. The dual-specificity protein tyrosine phosphatases are important to de-phosphorylate and inactivate the signaling components. In this study, we reported an atypical dual specificity protein tyrosine phosphatase ATPFA-DSP3 (DSP3), which loss-of-function mutant was insensitive to salt treatment, played a negative role in plant's response to salinity in Arabidopsis. DSP3 protein was primarily localized in nuclei and degraded after salt treatment. The level of ROS accumulation was lower in dsp3 mutant and higher in DSP3 over-expresser than wild type control, indicating DSP3 positively affect ROS production. DSP3 can directly interact with MPK3 and MPK6, and the phosphorylated MPK3 and MPK6 over accumulate in dsp3 mutant. Moreover, the phosphatase activity of DSP3 was required for its salt response. These results provide evidences showing that DSP3 negatively mediates plant salt response by directly modulating the accumulation of phosphorylated MPK3 and MPK6.

Protein tyrosine phosphatases play essential roles in plant growth and development and in plant responses to biotic or abiotic stresses. We recently demonstrated that an atypical dual-specificity protein tyrosine phosphatase in plants, AtPFA-DSP3 (DSP3), negatively regulates plant salt tolerance. Here, we report that a homolog of DSP3, AtPFA-DSP5 (DSP5), affects the response of plants to high-salt conditions. A loss-of-function mutant of DSP5 showed reduced sensitivity to salt treatment at the seed germination and vegetative stages of development while a gain-of-function mutant of DSP5 showed increased sensitivity to salt stress. The salt responses of dsp3dsp5 double-mutant plants were similar to those of dsp3 and dsp5 single-mutant plants. Gel overlay and firefly luciferase complementation assays showed that DSP5 interacts with MPK3 and MPK6 in vitro and in vivo . These results indicate that DSP5 is a novel negative regulator of salt responses in Arabidopsis that interacts directly with MPK3 and MPK6.