PtoWRKY40 interacts with PtoPHR1-LIKE3 while regulating the phosphate starvation response in poplar

Transcription factor CaPHR3 enhances phosphate starvation tolerance by up-regulating the expression of the CaPHT1;4 phosphate transporter gene in pepper

Plants frequently encounter phosphate (Pi) starvation due to its scarce availability in soil, necessitating an adaptive phosphate starvation response (PSR). This study explores this adaptation in pepper (Capsicum annuum L.) under low-Pi stress, focusing on the PHOSPHATE STARVATION RESPONSE (PHR) gene family. We observably halted shoot growth but promoted root elongation in pepper seedlings under low-Pi conditions, significantly impacting regulatory networks. Our research identified 13 PHR transcription factors in pepper, particularly noting that CaPHR3 rapidly up-regulates in response to low-Pi stress. Overexpressing CaPHR3 in Arabidopsis thaliana enhanced Pi starvation tolerance by modulating PSR-related genes and mitigated hypersensitivity in the Atphr1phl1 double mutant. Furthermore, CaPHR3 binds to the P1BS motif in the pepper PHOSPHATE TRANSPORTER 1;4 (PHT1;4) promoter to boost its expression under Pi deficiency. This activation increased Pi uptake and starvation tolerance when overexpressed. Overall, we pinpointed key players in the PSR mechanism through the CaPHR3-CaPHT1;4 pathway, contributing significantly to our understanding of Pi homeostasis and adaptive strategies in pepper under Pi-deficient conditions.

CsPHRs-CsJAZ3 incorporates phosphate signaling and jasmonate pathway to regulate catechin biosynthesis in Camellia sinensis

Catechins constitute abundant metabolites in tea and have potential health benefits and high economic value. Intensive study has shown that the biosynthesis of tea catechins is regulated by environmental factors and hormonal signals. However, little is known about the coordination of phosphate (Pi) signaling and the jasmonic acid (JA) pathway on biosynthesis of tea catechins. We found that Pi deficiency caused changes in the content of catechins and modulated the expression levels of genes involved in catechin biosynthesis. Herein, we identified two transcription factors of phosphate signaling in tea, named CsPHR1 and CsPHR2, respectively. Both regulated catechin biosynthesis by activating the transcription of CsANR1 and CsMYB5c. We further demonstrated CsSPX1, a Pi pathway repressor, suppressing the activation by CsPHR1/2 of CsANR1 and CsMYB5c. JA, one of the endogenous plant hormones, has been reported to be involved in the regulation of secondary metabolism. Our work demonstrated that the JA signaling repressor CsJAZ3 negatively regulated catechin biosynthesis via physical interaction with CsPHR1 and CsPHR2. Thus, the CsPHRs-CsJAZ3 module bridges the nutrition and hormone signals, contributing to targeted cultivation of high-quality tea cultivars with high fertilizer efficiency.

Characterization and stress-responsive regulation of CmPHT1 genes involved in phosphate uptake and transport in Melon (Cucumis melo L.)

BACKGROUND

Phosphorus (P) deficiency, a major nutrient stress, greatly hinders plant growth. Phosphate (Pi) uptake in plant roots relies on PHT1 family transporters. However, melon (Cucumis melo L.) lacks comprehensive identification and characterization of PHT1 genes, particularly their response patterns under diverse stresses.

RESULTS

This study identified and analyzed seven putative CmPHT1 genes on chromosomes 3, 4, 5, 6, and 7 using the melon genome. Phylogenetic analysis revealed shared motifs, domain compositions, and evolutionary relationships among genes with close histories. Exon number varied from 1 to 3. Collinearity analysis suggested segmental and tandem duplications as the primary mechanisms for CmPHT1 gene family expansion. CmPHT1;4 and CmPHT1;5 emerged as a tandemly duplicated pair. Analysis of cis-elements in CmPHT1 promoters identified 14 functional categories, including putative PHR1-binding sites (P1BS) in CmPHT1;4, CmPHT1;6, and CmPHT1;7. We identified that three WRKY transcription factors regulated CmPHT1;5 expression by binding to its W-box element. Notably, CmPHT1 promoters harbored cis-elements responsive to hormones and abiotic factors. Different stresses regulated CmPHT1 expression differently, suggesting that the adjusted expression patterns might contribute to plant adaptation.

CONCLUSIONS

This study unveils the characteristics, evolutionary diversity, and stress responsiveness of CmPHT1 genes in melon. These findings lay the foundation for in-depth investigations into their functional mechanisms in Cucurbitaceae crops.

WRKY33 negatively regulates anthocyanin biosynthesis and cooperates with PHR1 to mediate acclimation to phosphate starvation

Anthocyanin accumulation is acknowledged as a phenotypic indicator of phosphate (Pi) starvation. However, negative regulators of this process and their molecular mechanisms remain largely unexplored. In this study, we demonstrate that WRKY33 acts as a negative regulator of phosphorus-status-dependent anthocyanin biosynthesis. WRKY33 regulates the expression of the gene encoding dihydroflavonol 4-reductase (DFR), a rate-limiting enzyme in anthocyanin production, both directly and indirectly. WRKY33 binds directly to the DFR promoter to repress its expression and also interferes with the MBW complex through interacting with PAP1 to indirectly influence DFR transcriptional activation. Under -Pi conditions, PHR1 interacts with WRKY33, and the protein level of WRKY33 decreases; the repression of DFR expression by WRKY33 is thus attenuated, leading to anthocyanin accumulation in Arabidopsis. Further genetic and biochemical assays suggest that PHR1 is also involved in regulating factors that affect WRKY33 protein turnover. Taken together, our findings reveal that Pi starvation represses WRKY33, a repressor of anthocyanin biosynthesis, to finely tune anthocyanin biosynthesis. This "double-negative logic" regulation of phosphorus-status-dependent anthocyanin biosynthesis is required for the maintenance of plant metabolic homeostasis during acclimation to Pi starvation.

Phosphorus uptake, transport, and signaling in woody and model plants

Phosphorus (P), a critical macronutrient for plant growth and reproduction, is primarily acquired and translocated in the form of inorganic phosphate (Pi) by roots. Pi deficiency is widespread in many natural ecosystems, including forest plantations, due to its slow movement and easy fixation in soils. Plants have evolved complex and delicate regulation mechanisms on molecular and physiological levels to cope with Pi deficiency. Over the past two decades, extensive research has been performed to decipher the underlying molecular mechanisms that regulate the Pi starvation responses (PSR) in plants. This review highlights the prospects of Pi uptake, transport, and signaling in woody plants based on the backbone of model and crop plants. In addition, this review also highlights the interactions between phosphorus and other mineral nutrients such as Nitrogen (N) and Iron (Fe). Finally, this review discusses the challenges and potential future directions of Pi research in woody plants, including characterizing the woody-specific regulatory mechanisms of Pi signaling and evaluating the regulatory roles of Pi on woody-specific traits such as wood formation and ultimately generating high Phosphorus Use Efficiency (PUE) woody plants.

Multifaceted roles of WRKY transcription factors in abiotic stress and flavonoid biosynthesis

Increasing biotic and abiotic stresses are seriously impeding the growth and yield of staple crops and threatening global food security. As one of the largest classes of regulators in vascular plants, WRKY transcription factors play critical roles governing flavonoid biosynthesis during stress responses. By binding major W-box cis-elements (TGACCA/T) in target promoters, WRKYs modulate diverse signaling pathways. In this review, we optimized existing WRKY phylogenetic trees by incorporating additional plant species with WRKY proteins implicated in stress tolerance and flavonoid regulation. Based on the improved frameworks and documented results, we aim to deduce unifying themes of distinct WRKY subfamilies governing specific stress responses and flavonoid metabolism. These analyses will generate experimentally testable hypotheses regarding the putative functions of uncharacterized WRKY homologs in tuning flavonoid accumulation to enhance stress resilience.

The E3 ubiquitin ligase SINA1 and the protein kinase BIN2 cooperatively regulate PHR1 in apple anthocyanin biosynthesis

PHR1 (PHOSPHATE STARVATION RESPONSE1) plays key roles in the inorganic phosphate (Pi) starvation response and in Pi deficiency-induced anthocyanin biosynthesis in plants. However, the post-translational regulation of PHR1 is unclear, and the molecular basis of PHR1-mediated anthocyanin biosynthesis remains elusive. In this study, we determined that MdPHR1 was essential for Pi deficiency-induced anthocyanin accumulation in apple (Malus × domestica). MdPHR1 interacted with MdWRKY75, a positive regulator of anthocyanin biosynthesis, to enhance the MdWRKY75-activated transcription of MdMYB1, leading to anthocyanin accumulation. In addition, the E3 ubiquitin ligase SEVEN IN ABSENTIA1 (MdSINA1) negatively regulated MdPHR1-promoted anthocyanin biosynthesis via the ubiquitination-mediated degradation of MdPHR1. Moreover, the protein kinase apple BRASSINOSTEROID INSENSITIVE2 (MdBIN2) phosphorylated MdPHR1 and positively regulated MdPHR1-mediated anthocyanin accumulation by attenuating the MdSINA1-mediated ubiquitination degradation of MdPHR1. Taken together, these findings not only demonstrate the regulatory role of MdPHR1 in Pi starvation induced anthocyanin accumulation, but also provide an insight into the post-translational regulation of PHR1.

Progress in the understanding of WRKY transcription factors in woody plants

The WRKY transcription factor (TF) family, named for its iconic WRKY domain, is among the largest and most functionally diverse TF families in higher plants. WRKY TFs typically interact with the W-box of the target gene promoter to activate or inhibit the expression of downstream genes; these TFs are involved in the regulation of various physiological responses. Analyses of WRKY TFs in numerous woody plant species have revealed that WRKY family members are broadly involved in plant growth and development, as well as responses to biotic and abiotic stresses. Here, we review the origin, distribution, structure, and classification of WRKY TFs, along with their mechanisms of action, the regulatory networks in which they are involved, and their biological functions in woody plants. We consider methods currently used to investigate WRKY TFs in woody plants, discuss outstanding problems, and propose several new research directions. Our objective is to understand the current progress in this field and provide new perspectives to accelerate the pace of research that enable greater exploration of the biological functions of WRKY TFs.