The SPX domain-encoding proteins are believed to play important roles in phosphorus (Pi) homeostasis and signal transduction in plants. However, the overall information and responses of SPXs to phosphorus deficiency in pines, remain undefined. In this study, we screened the transcriptome data of Pinus massoniana in response to phosphorus deprivation. Ten SPX domain-containing genes were identified. Based on the conserved domains, the P. massoniana SPX genes were divided into four different subfamilies: SPX, SPX-MFS, SPX-EXS, and SPX-RING. RNA-seq analysis revealed that PmSPX genes were differentially expressed in response to phosphorus deprivation. Furthermore, real-time quantitative PCR (RT-qPCR) showed that PmSPX1 and PmSPX4 showed different expression patterns in different tissues under phosphorus stress. The promoter sequence of 2284 bp upstream of PmSPX1 was obtained by the genome walking method. A cis-element analysis indicated that there were several phosphorus stress response-related elements (e.g., two P1BS elements, a PHO element, and a W-box) in the promoter of PmSPX1. In addition, the previously obtained PmSPX2 promoter sequence contained a W-box, and it was shown that PmWRKY75 could directly bind to the PmSPX2 promoter using yeast one-hybrid analysis in this study. These results presented here revealed the foundational functions of PmSPXs in maintaining plant phosphorus homeostasis.
The Temporal Transcriptomic Response of Pinus massoniana Seedlings to Phosphorus Deficiency
