An MYB-Related Transcription Factor, UpMYB-PHL, Is Involved in Salt Tolerance by Coordinating Phosphorus Transporter and Energy Metabolism in Ulva prolifera

Ulva prolifera is the main causative species of marine green tides and exhibits extreme tolerance to intertidal abiotic stress. However, the underlying molecular mechanisms remain largely unclear. In this study, we cloned and characterized an MYB-related transcription factor, UpMYB-PHL, from U. prolifera. Expression analysis showed that UpMYB-PHL is rapidly and significantly induced by high-salt stress. Furthermore, heterologous overexpression of UpMYB-PHL in the model microalga Chlamydomonas reinhardtii significantly improved its salt tolerance and biomass. By yeast one-hybrid and dual-luciferase assays, we demonstrated that UpMYB-PHL directly binds to and activates the promoter of the phosphate transporter gene UpPHT1, which is a typical target gene of phosphate response (PHR) transcription factor and participates in salt stress responses of plants. Interestingly, yeast two-hybrid assays revealed that UpMYB-PHL physically interacts with UpGAPDH, a core enzyme in energy metabolism. Taken together, our findings reveal a novel regulatory network in which UpMYB-PHL coordinates phosphorus transporter and energy metabolism in response to salt stress in U. prolifera. This study provides a vital molecular explanation for the rapid adaptation and massive growth of U. prolifera under severe intertidal salt stress.