Phosphorus-induced change in root hair growth is associated with IAA accumulation in walnut

Walnut, an important non-wood product forest tree, has free root hairs in orchards. Root hairs are specialized cells originating from the root epidermis that are regulated by plant hormones, such as auxins. This study was conducted to evaluate the effect and mechanism of phosphorus stress on root hair growth of walnut (Juglans regia L.) seedings by auxin (IAA) biosynthesis and transport. Both low phosphorus (LP) and no phosphorus stresses (NP) heavily decreased plant height, leaf number, total root length, root surface, shoot and root biomass, and root nutrient contents. The LP treatment significantly increased root hair growth, accompanied with up-regulation of the positive regulation root hair growth gene JrCPC and down-regulation of the negative regulation root hair growth gene JrTTG1, while the NP treatment had opposite effects. The root IAA level, IAAO activities, IAA transport genes (JrAUX1, JrLAX1, and JrPIN1), and the biosynthesis genes (JrTAA1 and JrTAR1) were increased by the LP treatment, while the NP treatment decreased all of them. Interestingly, the auxin biosynthesis gene CsYUCCA1 was not affected, which suggested that P mainly affects root hair growth of walnut by regulating auxin transport, and then affects root nutrient absorption and plant growth.

Transcriptome-Wide Identification and Expression Profiling of SPX Domain-Containing Members in Responses to Phosphorus Deprivation of Pinus massoniana

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.