Phosphorus (P) is an essential macronutrient for plant growth and development. To adapt to low inorganic-phosphate (Pi) environments, plants have evolved complex mechanisms and pathways that regulate ...the acquisition and remobilization of Pi and maintain P homeostasis. These mechanisms are regulated by complex gene regulatory networks through the functions of Pi transporters (PTs) and Pi starvation-induced (PSI) genes. This review summarizes recent progress in determining the molecular regulatory mechanisms of phosphate transporters and the Pi signaling network in the dicot Arabidopsis (Arabidopsis thaliana) and the monocot rice (Oryza sativa L.). Recent advances in this field provide a reference for understanding plant Pi signaling and specific mechanisms that mediate plant adaptation to environments with limited Pi availability. We propose potential biotechnological applications of known genes to develop plant cultivars with improved Pi uptake and use efficiency.
The intrinsically disordered region (IDR) is a preserved signature of phytobacterial type III effectors (T3Es). The T3E IDR is thought to mediate unfolding during translocation into the host cell and ...to avoid host defense by sequence diversification. Here, we demonstrate a mechanism of host subversion via the T3E IDR. We report that the Xanthomonas campestris T3E XopR undergoes liquid-liquid phase separation (LLPS) via multivalent IDR-mediated interactions that hijack the Arabidopsis actin cytoskeleton. XopR is gradually translocated into host cells during infection and forms a macromolecular complex with actin-binding proteins at the cell cortex. By tuning the physical-chemical properties of XopR-complex coacervates, XopR progressively manipulates multiple steps of actin assembly, including formin-mediated nucleation, crosslinking of F-actin, and actin depolymerization, which occurs through competition for actin-depolymerizing factor and depends on constituent stoichiometry. Our findings unravel a sophisticated strategy in which bacterial T3E subverts the host actin cytoskeleton via protein complex coacervation.
Phosphorus (P) is an essential macronutrient for plant growth and development, but the molecular mechanism determining how plants sense external inorganic phosphate (Pi) levels and reprogram ...transcriptional and adaptive responses is incompletely understood.
In this study, we investigated the function of OsSPX6 (hereafter SPX6), an uncharacterized member of SPX domain (SYG1, Pho81 and XPR1)-containing proteins in rice, using reverse genetics and biochemical approaches.
Transgenic plants overexpressing SPX6 exhibited decreased Pi concentrations and suppression of phosphate starvation-induced (PSI) genes. By contrast, transgenic lines with decreased SPX6 transcript levels or spx6 mutant showed significant Pi accumulation in the leaf and upregulation of PSI genes. Overexpression of SPX6 genetically suppressed the overexpression of PHOSPHATE STARVATION RESPONSE REGULATOR 2 (PHR2) in terms of the accumulation of high Pi content. Moreover, direct interaction of SPX6 with PHR2 impeded PHR2 translocation into the nucleus, and inhibited PHR2 binding to the P1BS (PHR1 binding sequence) element. SPX6 protein was degraded in leaves under Pi-deficient conditions, whereas it accumulated in roots.
We conclude that rice SPX6 is another important negative regulator in Pi starvation signaling through the interaction with PHR2. SPX6 shows different responses to Pi starvation in shoot and root, which differ from those of other SPX proteins.
Soil contamination with arsenic (As) can cause phytotoxicity and elevated As accumulation in rice grain. Here, we used a forward genetics approach to investigate the mechanism of arsenate (As(V)) ...tolerance and accumulation in rice.
A rice mutant hypersensitive to As(V), but not to As(III), was isolated. Genomic resequencing and complementation tests were used to identify the causal gene. The function of the gene, its expression pattern and subcellular localization were characterized.
OsHAC4 is the causal gene for the As(V)-hypersensitive phenotype. The gene encodes a rhodanase-like protein that shows As(V) reductase activity when expressed in Escherichia coli. OsHAC4 was highly expressed in roots and was induced by As(V). In OsHAC4pro-GUS transgenic plants, the gene was expressed exclusively in the root epidermis and exodermis. OsHAC4-eGFP was localized in the cytoplasm and the nucleus. Mutation in OsHAC4 resulted in decreased As(V) reduction in roots, decreased As(III) efflux to the external medium and markedly increased As accumulation in rice shoots. Overexpression of OsHAC4 increased As (V) tolerance and decreased As accumulation in rice plants.
OsHAC4 is an As(V) reductase that is critical for As(V) detoxification and for the control of As accumulation in rice. As(V) reduction, followed by As(III) efflux, is an important mechanism of As(V) detoxification.
Membraneless organelles (MLO) regulate diverse biological processes in a spatiotemporally controlled manner spanning from inside to outside of the cells. The plasma membrane (PM) at the cell surface ...serves as a central platform for forming multi-component signaling hubs that sense mechanical and chemical cues during physiological and pathological conditions. During signal transduction, the assembly and formation of membrane-bound MLO are dynamically tunable depending on the physicochemical properties of the surrounding environment and partitioning biomolecules. Biomechanical properties of MLO-associated membrane structures can control the microenvironment for biomolecular interactions and assembly. Lipid-protein complex interactions determine the catalytic region's assembly pattern and assembly rate and, thereby, the amplitude of activities. In this review, we will focus on how cell surface microenvironments, including membrane curvature, surface topology and tension, lipid-phase separation, and adhesion force, guide the assembly of PM-associated MLO for cell signal transductions.
The assembly of macromolecules on the plasma membrane concentrates cell surface biomolecules into nanometer- to micrometer-scale clusters (nano- or microdomains) that help the cell initiate or ...respond to signals. In plant-microbe interactions, the actin cytoskeleton undergoes rapid remodeling during pathogen-associated molecular pattern-triggered immunity (PTI). The nanoclustering of formin-actin nucleator proteins at the cell surface has been identified as underlying actin nucleation during plant innate immune responses. Here, we show that the condensation of nanodomain constituents and the self-assembly of remorin proteins enables this mechanism of controlling formin condensation and activity during innate immunity in Arabidopsis thaliana. Through intrinsically disordered region-mediated remorin oligomerization and formin interaction, remorin gradually recruits and condenses formins upon PTI activation in lipid bilayers, consequently increasing actin nucleation in a time-dependent manner postinfection. Such nanodomain- and remorin-mediated regulation of plant surface biomolecules is expected to be a general feature of plant innate immune responses that creates spatially separated biochemical compartments and fine tunes membrane physicochemical properties for transduction of immune signals in the host.
Membraneless organelles (MLO) regulate diverse biological processes in a spatiotemporally controlled manner spanning from inside to outside of the cells. The plasma membrane (PM) at the cell surface ...serves as a central platform for forming multi-component signaling hubs that sense mechanical and chemical cues during physiological and pathological conditions. During signal transduction, the assembly and formation of membrane-bound MLO are dynamically tunable depending on the physicochemical properties of the surrounding environment and partitioning biomolecules. Biomechanical properties of MLO-associated membrane structures can control the microenvironment for biomolecular interactions and assembly. Lipid-protein complex interactions determine the catalytic region’s assembly pattern and assembly rate and, thereby, the amplitude of activities. In this review, we will focus on how cell surface microenvironments, including membrane curvature, surface topology and tension, lipid-phase separation, and adhesion force, guide the assembly of PM-associated MLO for cell signal transductions.
Ammonia (NH3) can be used as carbon-free alternative fuel for modern energy and transportation systems. Co-firing NH3 with syngas can overcome the high ignition energy and low burning velocities of ...pure NH3 flames on the one hand, while regarding the characteristics of syngas on the other hand, this strategy may have low-emission potential in real application, and a corresponding research can be helpful for validating or developing NH3 co-firing mechanisms with more complex fuels. The present study experimentally investigated laminar burning velocities of NH3/syngas/air flames at atmospheric pressure and 298 K using the heat flux method. Two types of syngas components were used, i.e., SYN_A: 5 vol% H2 + 95 vol% CO and SYN_B: 50 vol% H2 + 50 vol% CO, and the measured conditions cover wide ranges of mixing ratios and equivalence ratios. Several literature kinetic mechanisms were tested and a new mechanism was proposed. Results calculated by the present mechanism agree well with experimental data of the burning velocities and the ignition delay times of NH3, NH3/H2, NH3/CO, and NH3/syngas flames at various mixing ratios, equivalence ratios, and pressures. The present mechanism also reproduces the trend of NOx emission characteristic in literature. Detailed kinetic analyses using the present mechanism were carried out, showing the NH3 oxidation processes in NH3/syngas/air flames and the most rate-limiting reactions for predicting the laminar burning velocities. Important reactions with different rate parameters from different sources were labeled, which could be helpful for future organization or optimization of NH3 kinetic mechanisms.
Ammonia (NH3) is a promising carbon-free alternative fuel, and blending NH3 with other more active fuels can enhance the low burning rate of pure NH3 flames, which makes it more compatible with ...existing combustors. There are laminar burning velocity data of NH3+H2, NH3+CO/syngas, and NH3+CH4 flames in literature, however, blending NH3 with the oxygenated alternative fuel alcohols have not yet been checked. In the present work, the laminar burning velocities of NH3+CH3OH/air and NH3+C2H5OH/air flames were measured using the heat flux method at 1 atm with varied equivalence ratios and mixing ratios. Measurements were carried out at 298 K and elevated temperatures until 448 K unburnt temperatures, in order to check the data consistency via the temperature coefficient α in SLSL0=(TuTu0)α. A new updated kinetic mechanism, based on our previous mechanism named CEU-NH3, was proposed and validated based on the present and published experimental data for laminar burning velocity, ignition delay times and species profiles. This mechanism contains 91 species and 444 reactions, which is small in size and thus advantageous to be used in the modeling of complex combustion fields. By numerical analyses using the CEU-NH3 and the detailed Konnov mechanisms, the interactions between C- and N- containing species are found to be insignificant for the laminar burning velocities of the various NH3 blending mixtures.
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