Title: Phosphate-dependent regulation of vacuolar trafficking of OsSPX-MFSs is critical for maintaining intracellular phosphate homeostasis in rice

Runze Guo, Qi Zhang, Kun Qian, Yinghui Ying, Wenying Liao, Lening Gan, Chuanzao Mao, Yong Wang, James Whelan, Huixia Shou

Abstract

Vacuolar storage of phosphate (Pi) is essential for Pi homeostasis in plants. The SPX-MFS family proteins have been demonstrated as vacuolar Pi transporters in many plant species. Transcriptional regulation of the predominant transporter among rice SPX-MFSs, OsSPX-MFS3, was only moderately suppressed by Pi starvation. Thus, post-transcriptional mechanisms are hypothesized to regulate the activity of OsSPX-MFS3. We show that the tonoplast localization of OsSPX-MFSs is inhibited under Pi deplete conditions, and are retained in the pre-vacuolar compartments (PVCs). Using a yeast-two-hybrid screen, two SNAREs proteins, OsSYP21 and OsSYP22 were identified to interact with the MFS domain of OsSPX-MFS3 and facilitate the trafficking of OsSPX-MFS3 from the PVCs to the tonoplasts. While a homozygous frameshift mutation of OsSYP22 is lethal, the tonoplast localizations of OsSPX-MFS3 were significantly inhibited in the domain-negative form of OsSYP22 (OsSYP22-ND) transgenic plants, which consequently resulted in the reduction of vacuolar Pi concentrations in OsSYP22-ND plants. Under Pi deplete conditions, the interaction between OsSYP22 and OsSPX-MFS3 was disrupted, which depended on the presence of the SPX domain. Deleting the SPX domains of OsSPX-MFSs results in their tonoplast-localization under both Pi deplete and replete conditions. Complementation of the osspx-mfs1/2/3 triple mutants with the MFS domain or the SPX domain of OsSPX-MFS3 confirmed that the MFS and the SPX domains are responsive to the Pi transport activity and Pi dependent regulation, respectively. These data indicated that the SPX domains of OsSPX-MFSs sense cellular Pi (InsPs) levels, and under Pi deplete conditions inhibits the interaction between OsSPX-MFSs and OsSYP21/22, and subsequent trafficking of OsSPX-MFSs from the PVCs to the tonoplast.

Link: https://www.cell.com/molecular-plant/fulltext/S1674-2052(23)00206-X