OsJAZ11 regulates phosphate starvation responses in rice

Rice master regulator 'HYR' enhances growth and defense mechanisms with consequences for fall armyworm growth and host selection

Rice (Oryza sativa L.), the staple food for half of the world's population, suffers heavy damage by insect herbivores, especially the emerging fall armyworm (FAW), Spodoptera frugiperda. HIGHER YIELD RICE (HYR), a master regulator of multiple biological pathways with an established gene regulatory network, has been found to improve rice yield to ∼29% and tolerance to environmental stress. However, its impact on defense has not been explored. We hypothesized that, FAW would target HYR plants because of its vigorous growth and lead to trade-offs for defense. Through a series of experiments with HYR and its wild type (WT), we show that HYR plants have enhanced below-ground growth, physiological traits, and direct and indirect defense traits including leaf trichomes, wax, and volatile organic compounds. To test possible phytohormone-mediated defense signaling, we focussed on jasmonic acid and salicylic acid gene expression panel and found that most of these genes are highly expressed in HYR when compared to its WT counterpart. Bioassays examining developmental milestones also revealed that HYR plants effectively deter FAW, and when force-fed, caused negative effects. Collectively, our findings suggest that the master regulator HYR (Higher Yield Rice expressing) plants enhance growth and physiological traits, as well as physical and chemical defense mechanisms through co-ordinated defense gene expression, which deter herbivore feeding, growth, development, and host selection.

Optimizing plant phosphate uptake: Advances in the core regulatory mechanisms of phosphate starvation response proteins and their macromolecular partners: A review

Phosphorus (P), essential for plant survival, is primarily absorbed as inorganic phosphate (Pi), yet soil Pi scarcity severely limits plant growth and agricultural productivity. This review synthesizes current research on plant adaptations to Pi scarcity, with a focus on the root system as the primary site of Pi absorption and the role of MYB transcription factors, particularly PHOSPHATE STARVATION RESPONSE 1 (PHR1), a core regulatory biological macromolecule. PHR1 orchestrates a wide array of genetic responses that modify root architecture to enhance Pi acquisition under nutrient-poor conditions. This review delves into the biological activities, molecular associations, chemical and biological modifications, and functional properties of PHR1 and related MYB transcription factors, examining how these regulatory macromolecular proteins interact with other molecular components to form complexes that coordinate adaptive root development. By integrating findings from diverse plant species, the review highlights the potential of leveraging molecular breeding techniques to develop cultivars with enhanced phosphate uptake efficiency by targeting these regulatory macromolecular proteins. Such advancements promise to mitigate the impacts of Pi deficiency, supporting sustainable agricultural and forestry practices. The insights provided aim to inform and guide future research in plant nutrient management, focusing on the intricate interplay of biological and molecular factors that regulate phosphate uptake.

Genome-Wide Analysis of the JAZ Gene Family in Potato and Functional Verification of StJAZ23 Under Drought Stress

The JASMONATE-ZIM DOMAIN (JAZ) repressors are crucial proteins in the jasmonic acid signaling pathway that play a significant role in plant growth, development and response to abiotic stress (such as drought, heat, salinity, and low temperature). In this study, we identified 26 potato JAZ genes and classified the corresponding predicted proteins into five subfamilies. All potato JAZ proteins exhibited the expected conserved TIFY (TIF[F/Y] XG) and JAZ domains. Additionally, we identified several stress-responsive cis-regulatory elements, notably ABRE and ARE in the promoters of the JAZ gene family. Whole transcriptome and gene family expression analysis identified StJAZ23 as a key gene responding to drought stress in the root tissues of the Atlantic (Atl) and Qingshu 9 (QS9) potato cultivars. The StJAZ23 gene was cloned, and subcellular localization analysis suggested that the StJAZ23 protein was mainly localized in the nucleus and cell membrane. This study confirmed that StJAZ23 plays a role in drought stress by analyzing several StJAZ23 overexpression (OE-3, OE-5, and OE-6) and RNA interference (RNAi-3, RNAi-6, and RNAi-13) transgenic potato lines. The OE lines displayed significantly increased StJAZ23 expression compared to wild-type (WT) plants, while RNAi lines exhibited significantly reduced expression. The total root length, root tip count, and root surface area were significantly enhanced in OE lines under drought stress, compared to WT plants, whereas RNAi lines showed significant reductions. StJAZ23 overexpression also increased the activities of SOD, POD, CAT, and root vigor under drought stress and JA and ABA hormone levels were also significantly increased in roots under drought stress. These results highlight the positive role of the StJAZ23 gene in enhancing potato resilience to drought stress.

A lipid synthase maintains metabolic flux for jasmonate synthesis to regulate root growth and phosphate homeostasis

Plants require phosphate (Pi) for proper growth and development but often face scarcity of this vital nutrient in the soil. Pi starvation triggers membrane lipid remodeling to utilize the membrane phospholipid-bound Pi in plants. In this process, phospholipids are replaced by non-Pi-containing galactolipids (monogalactosyldiacylglycerol, MGDG; digalactosyldiacylglycerol, DGDG) and sulfolipids. The galactolipids ratio (MGDG:DGDG) is suggested to influence jasmonic acid (JA) biosynthesis. However, how the MGDG:DGDG ratio, JA levels, and root growth are coordinated under Pi deficiency in rice (Oryza sativa) remains unknown. Here, we characterized DGDG synthase 1 (OsDGD1) for its role in regulating root development by maintaining metabolic flux for JA biosynthesis. We showed that OsDGD1 is responsive under low Pi and is under the direct control of Phosphate Starvation Response 2, the master regulator of low Pi adaptations. Further, OsDGD1 knockout (KO) lines showed marked phenotypic differences compared to the wild type, including a significant reduction in root length and biomass, leading to reduced Pi uptake. Further, lipidome analyses revealed reduced DGDG levels in the KO line, leading to reduced membrane remodeling, thus affecting P utilization efficiency. We also observed an increase in the MGDG:DGDG ratio in KO lines, which enhanced the endogenous JA levels and signaling. This imbalance of JA in KO plants led to changes in auxin levels, causing drastic root growth inhibition. These findings indicate the critical role of OsDGD1 in maintaining optimum levels of JA during Pi deficiency for conducive root growth. Besides acting as signaling molecules and structural components, our study widens the role of lipids as metabolic flux controllers for phytohormone biosynthesis.

Phosphate deficiency inducible OsGDPD5 affects root growth by regulating sugar-auxin crosstalk

Glycerophosphodiester phosphodiesterases (GDPDs) enzymes are known to be involved in phospholipids degradation pathways, where glycerophosphodiesters are hydrolyzed to glycerol-3-phosphate (G3P) and corresponding alcohol. In plants, GDPDs are involved in phosphate deficiency adaptive responses and have been shown to impact root length, but the precise mechanism remains unclear. This study focuses on the rice GDPD5 gene and its role in regulating primary root growth. Our research demonstrates that OsGDPD5 encodes a functional GDPD enzyme and could hydrolyze glycerophosphocholine and glycerophosphorylethanolamine. At transcriptional levels, OsGDPD5 is preferentially expressed in the root tip and regulated by transcription factor OsPHR2. We have used CRISPR/Cas9 to generate OsGDPD5 knock-out lines, allowing us to explore its role in root growth. Our findings show that osgdpd5 mutants had a shorter primary root, which could be restored to a normal level by the exogenous application of sugar or G3P. Further, knocking out OsGDPD5 alters endogenous levels of G3P and sugars, affecting auxin biosynthesis in the root and, ultimately, primary root growth. In this manner, OsGDPD5 has a crucial role in regulating physiological processes, specifically sugar and auxin signaling, which are known to be involved in root growth regulation in rice. Our research thus unraveled a link between rice phosphate deficiency-responsive lipid remodeling and root growth via sugar-hormone signaling.

Developmental responses of roots to limited phosphate availability: Research progress and application in cereals

Phosphorus (P), an essential macronutrient, is crucial for plant growth and development. However, available inorganic phosphate (Pi) is often scarce in soil, and its limited mobility exacerbates P deficiency in plants. Plants have developed complex mechanisms to adapt to Pi-limited soils. The root, the primary interface of the plant with soil, plays an essential role in plant adaptation to Pi-limited soil environments. Root system architecture significantly influences Pi acquisition via the dynamic modulation of primary root and/or crown root length, lateral root proliferation and length, root hair development, and root growth angle in response to Pi availability. This review focuses on the physiological, anatomical, and molecular mechanisms underpinning changes in root development in response to Pi starvation in cereals, mainly focusing on the model monocot plant rice (Oryza sativa). We also review recent efforts to modify root architecture to enhance P uptake efficiency in crops and propose future research directions aimed at the genetic improvement of Pi uptake and use efficiency in crops based on root system architecture.

From trade-off to synergy: how nutrient status modulates plant resistance to herbivorous insects?

The principle of the "growth-defense trade-off" governs how plants adjust their growth and defensive strategies in response to external factors, impacting interactions among plants, herbivorous insects, and their natural enemies. Mineral nutrients are crucial in modulating plant growth and development through their bottom-up effects. Emerging evidence has revealed complex regulatory networks that link mineral nutrients to plant defense responses, influencing the delicate balance between growth and defense against herbivores. This review aims to summarize recent advances that elucidate the impact of nutrient availability on plant defense responses. Particularly, we focus on how nutrient status shapes plant resistance to herbivores, delving into the molecular mechanisms underlying this physiological process. Moreover, the interplay between mineral nutrients and various herbivore defense mechanisms, including physical protection, plant hormone signaling, defensive metabolite production, and volatile organic compound emissions that deter herbivores or attract their natural enemies, are discussed. This comprehensive review sets the stage for future investigations into the intricate crosstalk between nutrient signaling and plant defense responses, which serves as a central mechanism to guide sustainable pest management approaches, thereby promoting balanced agroecosystem health and enhancing plant ecosystem productivity and resilience.

OsMED14_2, a tail module subunit of Mediator complex, controls rice development and involves jasmonic acid

The Mediator complex is essential for eukaryotic transcription, yet its role and the function of its individual subunits in plants, especially in rice, remain poorly understood. Here, we investigate the function of OsMED14_2, a subunit of the Mediator tail module, in rice development. Overexpression and knockout of OsMED14_2 resulted in notable changes in panicle morphology and grain size. Microscopic analysis revealed impact of overexpression on pollen maturation, reflected by reduced viability, irregular shapes, and aberrant intine development. OsMED14_2 was found to interact with proteins involved in pollen development, namely, OsMADS62, OsMADS63 and OsMADS68, and its overexpression negatively affected the expression of OsMADS68 and the expression of other genes involved in intine development, including OsCAP1, OsGCD1, OsRIP1, and OsCPK29. Additionally, we found that OsMED14_2 overexpression influences jasmonic acid (JA) homeostasis, affecting bioactive JA levels, and expression of OsJAZ genes. Our data suggest OsMED14_2 may act as a regulator of JA-responsive genes through its interactions with OsHDAC6 and OsJAZ repressors. These findings contribute to better understanding of the Mediator complex's role in plant traits regulation.

PHOSPHATE1-mediated phosphate translocation from roots to shoots regulates floral transition in plants

Phosphorus nutrition has been known for a long time to influence floral transition in plants, but the underlying mechanism is unclear. Arabidopsis phosphate transporter PHOSPHATE1 (PHO1) plays a critical role in phosphate translocation from roots to shoots, but whether and how it regulates floral transition is unknown. Here, we show that knockout mutation of PHO1 delays flowering under both long- and short-day conditions. The late flowering of pho1 mutants can be partially rescued by Pi supplementation in rosettes or shoot apices. Grafting assay indicates that the late flowering of pho1 mutants is a result of impaired phosphate translocation from roots to shoots. Knockout mutation of SPX1 and SPX2, two negative regulators of the phosphate starvation response, partially rescues the late flowering of pho1 mutants. PHO1 is epistatic to PHO2, a negative regulator of PHO1, in flowering time regulation. Loss of PHO1 represses the expression of some floral activators, including FT encoding florigen, and induces the expression of some floral repressors in shoots. Genetic analyses indicate that at least jasmonic acid signaling is partially responsible for the late flowering of pho1 mutants. In addition, we find that rice PHO1;2, the homolog of PHO1, plays a similar role in floral transition. These results suggest that PHO1 integrates phosphorus nutrition and flowering time, and could be used as a potential target in modulating phosphorus nutrition-mediated flowering time in plants.

Rice A20/AN1 protein, OsSAP10, confers water-deficit stress tolerance via proteasome pathway and positive regulation of ABA signaling in Arabidopsis

KEY MESSAGE

Overexpression of rice A20/AN1 zinc-finger protein, OsSAP10, improves water-deficit stress tolerance in Arabidopsis via interaction with multiple proteins. Stress-associated proteins (SAPs) constitute a class of A20/AN1 zinc-finger domain containing proteins and their genes are induced in response to multiple abiotic stresses. The role of certain SAP genes in conferring abiotic stress tolerance is well established, but their mechanism of action is poorly understood. To improve our understanding of SAP gene functions, OsSAP10, a stress-inducible rice gene, was chosen for the functional and molecular characterization. To elucidate its role in water-deficit stress (WDS) response, we aimed to functionally characterize its roles in transgenic Arabidopsis, overexpressing OsSAP10. OsSAP10 transgenics showed improved tolerance to water-deficit stress at seed germination, seedling and mature plant stages. At physiological and biochemical levels, OsSAP10 transgenics exhibited a higher survival rate, increased relative water content, high osmolyte accumulation (proline and soluble sugar), reduced water loss, low ROS production, low MDA content and protected yield loss under WDS relative to wild type (WT). Moreover, transgenics were hypersensitive to ABA treatment with enhanced ABA signaling and stress-responsive genes expression. The protein-protein interaction studies revealed that OsSAP10 interacts with proteins involved in proteasomal pathway, such as OsRAD23, polyubiquitin and with negative and positive regulators of stress signaling, i.e., OsMBP1.2, OsDRIP2, OsSCP and OsAMTR1. The A20 domain was found to be crucial for most interactions but insufficient for all interactions tested. Overall, our investigations suggest that OsSAP10 is an important candidate for improving water-deficit stress tolerance in plants, and positively regulates ABA and WDS signaling via protein-protein interactions and modulation of endogenous genes expression in ABA-dependent manner.

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.

Wound-induced small-peptide-mediated signaling cascade, regulated by OsPSKR, dictates balance between growth and defense in rice

Wounding is a general stress in plants that results from various pest and pathogenic infections in addition to environment-induced mechanical damages. Plants have sophisticated molecular mechanisms to recognize and respond to wounding, with those of monocots being distinct from dicots. Here, we show the involvement of two distinct categories of temporally separated, endogenously derived peptides, namely, plant elicitor peptides (PEPs) and phytosulfokine (PSK), mediating wound responses in rice. These peptides trigger a dynamic signal relay in which a receptor kinase involved in PSK perception named OsPSKR plays a major role. Perturbation of OsPSKR expression in rice leads to compromised development and constitutive autoimmune phenotypes. OsPSKR regulates the transitioning of defense to growth signals upon wounding. OsPSKR displays mutual antagonism with the OsPEPR1 receptor involved in PEP perception. Collectively, our work indicates the presence of a stepwise peptide-mediated signal relay that regulates the transition from defense to growth upon wounding in monocots.

Phosphate deficiency increases plant susceptibility to Botrytis cinerea infection by inducing the abscisic acid pathway

Plants have evolved finely regulated defense systems to counter biotic and abiotic threats. In the natural environment, plants are typically challenged by simultaneous stresses and, amid such conditions, crosstalk between the activated signaling pathways becomes evident, ultimately altering the outcome of the defense response. As an example of combined biotic and abiotic stresses, inorganic phosphate (Pi) deficiency, common in natural and agricultural environments, can occur along with attack by the fungus Botrytis cinerea, a devastating necrotrophic generalist pathogen responsible for massive crop losses. We report that Pi deficiency in Arabidopsis thaliana increases its susceptibility to infection by B. cinerea by influencing the early stages of pathogen infection, namely spore adhesion and germination on the leaf surface. Remarkably, Pi-deficient plants are more susceptible to B. cinerea despite displaying the appropriate activation of the jasmonic acid and ethylene signaling pathways, as well as producing secondary defense metabolites and reactive oxygen species. Conversely, the callose deposition in response to B. cinerea infection is compromised under Pi-deficient conditions. The levels of abscisic acid (ABA) are increased in Pi-deficient plants, and the heightened susceptibility to B. cinerea observed under Pi deficiency can be reverted by blocking ABA biosynthesis. Furthermore, high level of leaf ABA induced by overexpression of NCED6 in Pi-sufficient plants also resulted in greater susceptibility to B. cinerea infection associated with increased spore adhesion and germination, and reduced callose deposition. Our findings reveal a link between the enhanced accumulation of ABA induced by Pi deficiency and an increased sensitivity to B. cinerea infection.

The Oryza sativa transcriptome responds spatiotemporally to polystyrene nanoplastic stress

Nanoplastic represents an emerging abiotic stress facing modern agriculture, impacting global crop production. However, the molecular response of crop plants to this stress remains poorly understood at a spatiotemporal resolution. We therefore used RNA sequencing to profile the transcriptome expressed in rice (Oryza sativa) root and leaf organs at 1, 2, 4, and 8 d post exposure with nanoplastic. We revealed a striking similarity between the rice biomass dynamics in aboveground parts to that in belowground parts during nanoplastic stress, but transcriptome did not. At the global transcriptomic level, a total of 2332 differentially expressed genes were identified, with the majority being spatiotemporal specific, reflecting that nanoplastics predominantly regulate three processes in rice seedlings: (1) down-regulation of chlorophyll biosynthesis, photosynthesis, and starch, sucrose and nitrogen metabolism, (2) activation of defense responses such as brassinosteroid biosynthesis and phenylpropanoid biosynthesis, and (3) modulation of jasmonic acid and cytokinin signaling pathways by transcription factors. Notably, the genes involved in plant-pathogen interaction were shown to be successively modulated by both root and leaf organs, particularly plant disease defense genes (OsWRKY24, OsWRKY53, Os4CL3, OsPAL4, and MPK5), possibly indicating that nanoplastics affect rice growth indirectly through other biota. Finally, we associated biomass phenotypes with the temporal reprogramming of rice transcriptome by weighted gene co-expression network analysis, noting a significantly correlation with photosynthesis, carbon metabolism, and phenylpropanoid biosynthesis that may reflect the mechanisms of biomass reduction. Functional analysis further identified PsbY, MYB, cytochrome P450, and AP2/ERF as hub genes governing these pathways. Overall, our work provides the understanding of molecular mechanisms of rice in response to nanoplastics, which in turn suggests how rice might behave in a nanoplastic pollution scenario.

Modulation of plant immunity and biotic interactions under phosphate deficiency

Phosphorus (P) is an essential macronutrient for plant life and growth. P is primarily acquired in the form of inorganic phosphate (Pi) from soil. To cope with Pi deficiency, plants have evolved an elaborate system to improve Pi acquisition and utilization through an array of developmental and physiological changes, termed Pi starvation response (PSR). Plants also assemble and manage mutualistic microbes to enhance Pi uptake, through integrating PSR and immunity signaling. A trade-off between plant growth and defense favors the notion that plants lower a cellular state of immunity to accommodate host-beneficial microbes for nutrition and growth at the cost of infection risk. However, the existing data indicate that plants selectively activate defense responses against pathogens, but do not or less against non-pathogens, even under nutrient deficiency. In this review, we highlight recent advances in the principles and mechanisms with which plants balance immunity and growth-related processes to optimize their adaptation to Pi deficiency.

SUMOylation of OsPSTOL1 is essential for regulating phosphate starvation responses in rice and Arabidopsis

Although rice is one of the main sources of calories for most of the world, nearly 60% of rice is grown in soils that are low in phosphorus especially in Asia and Africa. Given the limitations of bioavailable inorganic phosphate (Pi) in soils, it is important to develop crops tolerant to low phosphate in order to boost food security. Due to the immobile nature of Pi, plants have developed complex molecular signalling pathways that allow them to discern changes in Pi concentrations in the environment and adapt their growth and development. Recently, in rice, it was shown that a specific serine-threonine kinase known as Phosphorus-starvation tolerance 1 (PSTOL1) is important for conferring low phosphate tolerance in rice. Nonetheless, knowledge about the mechanism underpinning PSTOL1 activity in conferring low Pi tolerance is very limited in rice. Post-translation modifications (PTMs) play an important role in plants in providing a conduit to detect changes in the environment and influence molecular signalling pathways to adapt growth and development. In recent years, the PTM SUMOylation has been shown to be critical for plant growth and development. It is known that plants experience hyperSUMOylation of target proteins during phosphate starvation. Here, we demonstrate that PSTOL1 is SUMOylated in planta, and this affects its phosphorylation activity. Furthermore, we also provide new evidence for the role of SUMOylation in regulating PSTOL1 activity in plant responses to Pi starvation in rice and Arabidopsis. Our data indicated that overexpression of the non-SUMOylatable version of OsPSTOL1 negatively impacts total root length and total root surface area of rice grown under low Pi. Interestingly, our data also showed that overexpression of OsPSTOL1 in a non-cereal species, Arabidopsis, also positively impacts overall plant growth under low Pi by modulating root development. Taken together our data provide new evidence for the role of PSTOL1 SUMOylation in mediating enhanced root development for tolerating phosphate-limiting conditions.

Dynamic interactions between SPX proteins, the ubiquitination machinery, and signalling molecules for stress adaptation at a whole-plant level

The plant macronutrient phosphorus is a scarce resource and plant-available phosphate is limiting in most soil types. Generally, a gene regulatory module called the phosphate starvation response (PSR) enables efficient phosphate acquisition by roots and translocation to other organs. Plants growing on moderate to nutrient-rich soils need to co-ordinate availability of different nutrients and repress the highly efficient PSR to adjust phosphate acquisition to the availability of other macro- and micronutrients, and in particular nitrogen. PSR repression is mediated by a small family of single SYG1/Pho81/XPR1 (SPX) domain proteins. The SPX domain binds higher order inositol pyrophosphates that signal cellular phosphorus status and modulate SPX protein interaction with PHOSPHATE STARVATION RESPONSE1 (PHR1), the central transcriptional regulator of PSR. Sequestration by SPX repressors restricts PHR1 access to PSR gene promoters. Here we focus on SPX4 that primarily acts in shoots and sequesters many transcription factors other than PHR1 in the cytosol to control processes beyond the classical PSR, such as nitrate, auxin, and jasmonic acid signalling. Unlike SPX1 and SPX2, SPX4 is subject to proteasomal degradation not only by singular E3 ligases, but also by SCF-CRL complexes. Emerging models for these different layers of control and their consequences for plant acclimation to the environment will be discussed.

A tau class glutathione S-transferase in tea plant, CsGSTU45, facilitates tea plant susceptibility to Colletotrichum camelliae infection mediated by jasmonate signaling pathway

Tea plant [Camellia sinensis (L.) O. Kuntze], as one of the most important commercial crops, frequently suffers from anthracnose caused by Colletotrichum camelliae. The plant-specific tau (U) class of glutathione S-transferases (GSTU) participates in ROS homeostasis. Here, we identified a plant-specific GST tau class gene from tea plant, CsGSTU45, which is induced by various stresses, including C. camelliae infection, by analyzing multiple transcriptomes. CsGSTU45 plays a negative role in disease resistance against C. camelliae by accumulating H2 O2 . JA negatively regulates the resistance of tea plants against C. camelliae, which depends on CsGSTU45. CsMYC2.2, which is the key regulator in the JA signaling pathway, directly binds to and activates the promoter of CsGSTU45. Furthermore, silencing CsMYC2.2 increased disease resistance associated with reduced transcript and protein levels of CsGSTU45, and decreased contents of H2 O2 . Therefore, CsMYC2.2 suppresses disease resistance against C. camelliae by binding to the promoter of the CsGSTU45 gene and activating CsGSTU45. CsJAZ1 interacts with CsMYC2.2. Silencing CsJAZ1 attenuates disease resistance, upregulates the expression of CsMYC2.2 elevates the level of the CsGSTU45 protein, and promotes the accumulation of H2 O2 . As a result, CsJAZ1 interacts with CsMYC2.2 and acts as its repressor to suppress the level of CsGSTU45 protein, eventually enhancing disease resistance in tea plants. Taken together, the results show that the JA signaling pathway mediated by CsJAZ1-CsMYC2.2 modulates tea plant susceptibility to C. camelliae by regulating CsGSTU45 to accumulate H2 O2 .

Genome-Wide Identification and Functional Analysis of the TIFY Family Genes in Response to Abiotic Stresses and Hormone Treatments in Tartary Buckwheat (Fagopyrum tataricum)

TIFY is a plant-specific gene family with four subfamilies: ZML, TIFY, PPD, and JAZ. Recently, this family was found to have regulatory functions in hormone stimulation, environmental response, and development. However, little is known about the roles of the TIFY family in Tartary buckwheat (Fagopyrum tataricum), a significant crop for both food and medicine. In this study, 18 TIFY family genes (FtTIFYs) in Tartary buckwheat were identified. The characteristics, motif compositions, and evolutionary relationships of the TIFY proteins, as well as the gene structures, cis-acting elements, and synteny of the TIFY genes, are discussed in detail. Moreover, we found that most FtTIFYs responded to various abiotic stresses (cold, heat, salt, or drought) and hormone treatments (ABA, MeJA, or SA). Through yeast two-hybrid assays, we revealed that two FtTIFYs, FtTIFY1 and FtJAZ7, interacted with FtABI5, a homolog protein of AtABI5 involved in ABA-mediated germination and stress responses, implying crosstalk between ABA and JA signaling in Tartary buckwheat. Furthermore, the overexpression of FtJAZ10 and FtJAZ12 enhanced the heat stress tolerance of tobacco. Consequently, our study suggests that the FtTIFY family plays important roles in responses to abiotic stress and provides two candidate genes (FtJAZ10 and FtJAZ12) for the cultivation of stress-resistant crops.

PHOSPHATE STARVATION RESPONSE1 (PHR1) interacts with JASMONATE ZIM-DOMAIN (JAZ) and MYC2 to modulate phosphate deficiency-induced jasmonate signaling in Arabidopsis

Phosphorus (P) is a macronutrient necessary for plant growth and development. Inorganic phosphate (Pi) deficiency modulates the signaling pathway of the phytohormone jasmonate in Arabidopsis thaliana, but the underlying molecular mechanism currently remains elusive. Here, we confirmed that jasmonate signaling was enhanced under low Pi conditions, and the CORONATINE INSENSITIVE1 (COI1)-mediated pathway is critical for this process. A mechanistic investigation revealed that several JASMONATE ZIM-DOMAIN (JAZ) repressors physically interacted with the Pi signaling-related core transcription factors PHOSPHATE STARVATION RESPONSE1 (PHR1), PHR1-LIKE2 (PHL2), and PHL3. Phenotypic analyses showed that PHR1 and its homologs positively regulated jasmonate-induced anthocyanin accumulation and root growth inhibition. PHR1 stimulated the expression of several jasmonate-responsive genes, whereas JAZ proteins interfered with its transcriptional function. Furthermore, PHR1 physically associated with the basic helix-loop-helix (bHLH) transcription factors MYC2, MYC3, and MYC4. Genetic analyses and biochemical assays indicated that PHR1 and MYC2 synergistically increased the transcription of downstream jasmonate-responsive genes and enhanced the responses to jasmonate. Collectively, our study reveals the crucial regulatory roles of PHR1 in modulating jasmonate responses and provides a mechanistic understanding of how PHR1 functions together with JAZ and MYC2 to maintain the appropriate level of jasmonate signaling under conditions of Pi deficiency.

Advances in Plant Lipid Metabolism Responses to Phosphate Scarcity

Low phosphate (Pi) availability in soils severely limits crop growth and production. Plants have evolved to have numerous physiological and molecular adaptive mechanisms to cope with Pi starvation. The release of Pi from membrane phospholipids is considered to improve plant phosphorus (P) utilization efficiency in response to Pi starvation and accompanies membrane lipid remodeling. In this review, we summarize recent discoveries related to this topic and the molecular basis of membrane phospholipid alteration and triacylglycerol metabolism in response to Pi depletion in plants at different subcellular levels. These findings will help to further elucidate the molecular mechanisms underlying plant adaptation to Pi starvation and thus help to develop crop cultivars with high P utilization efficiency.

Monogalactosyl diacylglycerol synthase 3 affects phosphate utilization and acquisition in rice

Galactolipids are essential to compensate for the loss of phospholipids by 'membrane lipid remodelling' in plants under phosphorus (P) deficiency conditions. Monogalactosyl diacylglycerol (MGDG) synthases catalyse the synthesis of MGDG which is further converted into digalactosyl diacylglycerol (DGDG), later replacing phospholipids in the extraplastidial membranes. However, the roles of these enzymes are not well explored in rice. In this study, the rice MGDG synthase 3 gene (OsMGD3) was identified and functionally characterized. We showed that the plant phosphate (Pi) status and the transcription factor PHOSPHATE STARVATION RESPONSE 2 (OsPHR2) are involved in the transcriptional regulation of OsMGD3. CRISPR/Cas9 knockout and overexpression lines of OsMGD3 were generated to explore its potential role in rice adaptation to Pi deficiency. Compared with the wild type, OsMGD3 knockout lines displayed a reduced Pi acquisition and utilization while overexpression lines showed an enhancement of the same. Further, OsMGD3 showed a predominant role in roots, altering lateral root growth. Our comprehensive lipidomic analysis revealed a role of OsMGD3 in membrane lipid remodelling, in addition to a role in regulating diacylglycerol and phosphatidic acid contents that affected the expression of Pi transporters. Our study highlights the role of OsMGD3 in affecting both internal P utilization and P acquisition in rice.

Ethylene inhibits rice root elongation in compacted soil via ABA- and auxin-mediated mechanisms

Intensive agriculture and changing tillage practices are causing soils to become increasingly compacted. Hard soils cause roots to accumulate the hormone ethylene, triggering reduced root elongation and increased radial swelling. We demonstrate that ethylene regulates these distinct root growth responses using different downstream signals, auxin, and abscisic acid (ABA). Auxin is primarily required to reduce cell elongation during a root compaction response, whereas ABA promotes radial cell expansion. Radial swelling was originally thought to aid root penetration in hard soil, yet rice ABA-deficient mutants disrupted in radial swelling of root tips penetrate compacted soil better than wild-type plants. The combined growth responses to auxin and ABA function to reduce the ability of roots to penetrate compacted soil.

Soil compaction represents a major agronomic challenge, inhibiting root elongation and impacting crop yields. Roots use ethylene to sense soil compaction as the restricted air space causes this gaseous signal to accumulate around root tips. Ethylene inhibits root elongation and promotes radial expansion in compacted soil, but its mechanistic basis remains unclear. Here, we report that ethylene promotes abscisic acid (ABA) biosynthesis and cortical cell radial expansion. Rice mutants of ABA biosynthetic genes had attenuated cortical cell radial expansion in compacted soil, leading to better penetration. Soil compaction-induced ethylene also up-regulates the auxin biosynthesis gene OsYUC8. Mutants lacking OsYUC8 are better able to penetrate compacted soil. The auxin influx transporter OsAUX1 is also required to mobilize auxin from the root tip to the elongation zone during a root compaction response. Moreover, osaux1 mutants penetrate compacted soil better than the wild-type roots and do not exhibit cortical cell radial expansion. We conclude that ethylene uses auxin and ABA as downstream signals to modify rice root cell elongation and radial expansion, causing root tips to swell and reducing their ability to penetrate compacted soil.

OsJAZ11 regulates spikelet and seed development in rice

Seed size is one of the major determinants of seed weight and eventually, crop yield. As the global population is increasing beyond the capacity of current food production, enhancing seed size is a key target for crop breeders. Despite the identification of several genes and QTLs, current understanding about the molecular regulation of seed size/weight remains fragmentary. In the present study, we report novel role of a jasmonic acid (JA) signaling repressor, OsJAZ11 controlling rice seed width and weight. Transgenic rice lines overexpressing OsJAZ11 exhibited up to a 14% increase in seed width and ~30% increase in seed weight compared to wild type (WT). Constitutive expression of OsJAZ11 dramatically influenced spikelet morphogenesis leading to extra glume-like structures, open hull, and abnormal numbers of floral organs. Furthermore, overexpression lines accumulated higher JA levels in spikelets and developing seeds. Expression studies uncovered altered expression of JA biosynthesis/signaling and MADS box genes in overexpression lines compared to WT. Yeast two-hybrid and pull-down assays revealed that OsJAZ11 interacts with OsMADS29 and OsMADS68. Remarkably, expression of OsGW7, a key negative regulator of grain size, was significantly reduced in overexpression lines. We propose that OsJAZ11 participates in the regulation of seed size and spikelet development by coordinating the expression of JA-related, OsGW7 and MADS genes.

Regulation and integration of plant jasmonate signaling: a comparative view of monocot and dicot

The phytohormone jasmonate plays a pivotal role in various aspects of plant life, including developmental programs and defense against pests and pathogens. A large body of knowledge on jasmonate biosynthesis, signal transduction as well as its functions in diverse plant processes has been gained in the past two decades. In addition, there exists extensive crosstalk between jasmonate pathway and other phytohormone pathways, such as salicylic acid (SA) and gibberellin (GA), in co-regulation of plant immune status, fine-tuning the balance of plant growth and defense, and so on, which were mostly learned from studies in the dicotyledonous model plants Arabidopsis thaliana and tomato but much less in monocot. Interestingly, existing evidence suggests both conservation and functional divergence in terms of core components of jasmonate pathway, its biological functions and signal integration with other phytohormones, between monocot and dicot. In this review, we summarize the current understanding on JA signal initiation, perception and regulation, and highlight the distinctive characteristics in different lineages of plants.

Plant phosphate nutrition: sensing the stress

Phosphorus (P) is obtained by plants as phosphate (Pi) from the soil and low Pi levels affects plant growth and development. Adaptation to low Pi condition entails sensing internal and external Pi levels and translating those signals to molecular and morphophysiological changes in the plant. In this review, we present findings related to local and systemin Pi sensing with focus the molecular mechanisms behind root system architectural changes and the impact of hormones and epigenetic mechanisms affecting those changes. We also present some of the recent advances in the Pi sensing and signaling mechanisms focusing on inositol pyrophosphate InsP8 and its interaction with SPX domain proteins to regulate the activity of the central regulator of the Pi starvation response, PHR.