Combined metabolomic and transcriptomic analysis evidences the interaction between sugars and phosphate in rice

Transcriptome analysis with different leaf blades identifies the phloem-specific phosphate transporter OsPHO1;3 required for phosphate homeostasis in rice

Phosphate (Pi) is essential for plant growth and development. One strategy to improve Pi use efficiency is to enhance Pi remobilization among leaves. Using transcriptome analysis with first (top) and fourth (down) leaf blades from rice (Oryza sativa) in Pi-sufficient and deficient conditions, we identified 1384 genes differentially expressed among these leaf blades. These genes were involved in physiological processes, metabolism, transport, and photosynthesis. Moreover, we identified the Pi efflux transporter gene, OsPHO1;3, responding to Pi-supplied conditions among these leaf blades. OsPHO1;3 is highly expressed in companion cells of phloem, but not xylem, in leaf blades and induced by Pi starvation. Mutation of OsPHO1;3 led to Pi accumulation in second to fourth leaves under Pi-sufficient conditions, but enhanced Pi levels in first leaves under Pi-deficient conditions. These Pi accumulations in leaves of Ospho1;3 mutants resulted from induction of OsPHT1;2 and OsPHT1;8 in root and reduction of Pi remobilization in leaf blades, revealed by the decreased Pi in phloem of leaves. Importantly, lack of OsPHO1;3 caused growth defects under a range of Pi-supplied conditions. These results demonstrate that Pi remobilization is essential for Pi homeostasis and plant growth irrespective of Pi-supplied conditions, and OsPHO1;3 plays an essential role in Pi remobilization for normal plant growth.

Understanding how various forms of phosphorus stress affect microbiome functions and boost plant disease resistance: Insights from metagenomic analysis

The plant's response to phosphorus (P) starvation suppresses its immunity and regulates rhizosphere microbial colonization. However, the impact of various P forms on plant disease resistance and microbial composition remains underreported. This paper examines the soybean rhizosphere microbiome facing co-stress from Fusarium oxysporum and diverse P forms. Macrogenomic analysis evaluates whether P addition enhances plant disease resistance and rhizosphere microbial function, and if such effects relate to P forms. Results show that different P forms mitigate F. oxysporum-induced plant inhibition by promoting P turnover. P forms predominantly affect microbial composition, followed by soil and plant properties. In soybean, the phosphate transport strategy (ugpA/Q) was selected to maintain high P to enhance immunity in the KH2PO4 treatment, while organo-P mineralization (phnH/F/W/G) was selected for superphosphate treatment. The Frankiales, a P-turnover microorganism, copiotrophic microorganisms, and indicator bacteria of plant properties, initially increase after F. oxysporum inoculation and then decrease post P addition, regardless of P forms. Additionally, the rhizosphere microbial community's metabolic activities and compounds significantly aid soybean defense against F. oxysporum, with functional types depending on P forms. Therefore, these findings establish a novel approach to enhance host defense against soil-borne diseases through P nutrition regulation to mediate host-driven metabolic activities of microbial communities.

Phosphorus deficiency alters root length, acid phosphatase activity, organic acids, and metabolites in root exudates of soybean cultivars

Phosphorus (P) deficiency alters the root morphological and physiological traits of plants. This study investigates how soybean cultivars with varying low-P tolerance values respond to different P levels in hydroponic culture by assessing alterations in root length, acid phosphatase activity, organic acid exudation, and metabolites in root exudates. Three low-P-tolerant cultivars ('Maetsue,' 'Kurotome,' and 'Fukuyutaka') and three low-P-sensitive cultivars ('Ihhon,' 'Chizuka,' and 'Komuta') were grown under 0 (P0) and 258 μM P (P8) for 7 and 14 days after transplantation (DAT). Low-P-tolerant cultivars increased root length by 31% and 119%, which was lower than the 62% and 144% increases in sensitive cultivars under P0 compared to P8 at 7 and 14 DAT, respectively. Acid phosphatase activity in low-P-tolerant cultivars exceeded that in sensitive cultivars by 5.2-fold and 2.0-fold at 7 and 14 DAT. Root exudates from each cultivar revealed 177 metabolites, with higher organic acid exudation in low-P-tolerant than sensitive cultivars under P0. Low-P-tolerant cultivars increased concentrations of specific metabolites (oxalate, GABA, quinate, citrate, AMP, 4-pyridoxate, and CMP), distinguishing them from low-P-sensitive cultivars under P0. The top five metabolomic pathways (purine metabolism, arginine and proline metabolism, TCA cycle, glyoxylate and dicarboxylate metabolism, alanine, aspartate, and glutamate metabolism) were more pronounced in low-P-tolerant cultivars at 14 DAT. These findings indicate that increasing root length was not an adaptation strategy under P deficiency; instead, tolerant cultivars exhibit enhanced root physiological traits, including increased acid phosphatase activity, organic acid exudation, specific metabolite release, and accelerated metabolic pathways under P deficiency.

Plant phosphate status influences root biotic interactions

Phosphorus (P) deficiency stress in combination with biotic stress(es) severely impacts crop yield. Plant responses to P deficiency overlapping with that of other stresses exhibit a high degree of complexity involving different signaling pathways. On the one hand, plants engage with rhizosphere microbiome/arbuscular mycorrhizal fungi for improved phosphate (Pi) acquisition and plant stress response upon Pi deficiency; on the other hand, this association is gets disturbed under Pi sufficiency. This nutrient-dependent response is highly regulated by the phosphate starvation response (PSR) mediated by the master regulator, PHR1, and its homolog, PHL. It is interesting to note that Pi status (deficiency/sufficiency) has a varying response (positive/negative) to different biotic encounters (beneficial microbes/opportunistic pathogens/insect herbivory) through a coupled PSR-PHR1 immune system. This also involves crosstalk among multiple players including transcription factors, defense hormones, miRNAs, and Pi transporters, among others influencing the plant-biotic-phosphate interactions. We provide a comprehensive view of these key players involved in maintaining a delicate balance between Pi homeostasis and plant immunity. Finally, we propose strategies to utilize this information to improve crop resilience to Pi deficiency in combination with biotic stresses.

Multi-omics-based identification of purple acid phosphatases and metabolites involved in phosphorus recycling in stylo root exudates

Stylo (Stylosanthes guianensis) is a tropical forage and cover crop that possesses low phosphate (Pi) tolerance traits. However, the mechanisms underlying its tolerance to low-Pi stress, particularly the role of root exudates, remain unclear. This study employed an integrated approach using physiological, biochemical, multi-omics, and gene function analyses to investigate the role of stylo root exudates in response to low-Pi stress. Widely targeted metabolomic analysis revealed that eight organic acids and one amino acid (L-cysteine) were significantly increased in the root exudates of Pi-deficient seedlings, among which tartaric acid and L-cysteine had strong abilities to dissolve insoluble-P. Furthermore, flavonoid-targeted metabolomic analysis identified 18 flavonoids that were significantly increased in root exudates under low-Pi conditions, mainly belonging to the isoflavonoid and flavanone subclasses. Additionally, transcriptomic analysis revealed that 15 genes encoding purple acid phosphatases (PAPs) had upregulated expression in roots under low-Pi conditions. Among them, SgPAP10 was characterized as a root-secreted phosphatase, and overexpression of SgPAP10 enhanced organic-P utilization by transgenic Arabidopsis. Overall, these findings provide detailed information regarding the importance of stylo root exudates in adaptation to low-Pi stress, highlighting the plant's ability to release Pi from organic-P and insoluble-P sources through root-secreted organic acids, amino acids, flavonoids, and PAPs.