Photosynthetic-Product-Dependent Activation of Plasma Membrane H+-ATPase and Nitrate Uptake in Arabidopsis Leaves

Chloroplast envelope K+/H+ antiporters are involved in cytosol pH regulation

Variations in light intensity induce cytosol pH changes in photosynthetic tissues, providing a possible signal to adjust a variety of biochemical, physiological and developmental processes to the energy status of the cells. It was shown that these pH changes are partially due to the transport of protons in or out of the thylakoid lumen. However, the ion transporters in the chloroplast that transmit these pH changes to the cytosol are not known. KEA1 and KEA2 are K+/H+ antiporters in the chloroplast inner envelope that adjust stromal pH in light-to-dark transitions. We previously determined that stromal pH is higher in kea1kea2 mutant cells. In this study, we now show that KEA1 and KEA2 are required to attenuate cytosol pH variations upon sudden light intensity changes in leaf mesophyll cells, showing they are important components of the light-modulated pH signalling module. The kea1kea2 mutant mesophyll cells also have a considerably less negative membrane potential. Membrane potential is dependent on the activity of the plasma membrane proton ATPase and is regulated by secondary ion transporters, mainly potassium channels in the plasma membrane. We did not find significant differences in the activity of the plasma membrane proton pump but found a strongly increased membrane permeability to protons, especially potassium, of the double mutant plasma membranes. Our results indicate that chloroplast envelope K+/H+ antiporters not only affect chloroplast pH but also have a strong impact on cellular ion homeostasis and energization of the plasma membrane.

Plasma membrane H+-ATPases in mineral nutrition and crop improvement

Plasma membrane H+-ATPases (PMAs) pump H+ out of the cytoplasm by consuming ATP to generate a membrane potential and proton motive force for the transmembrane transport of nutrients into and out of plant cells. PMAs are involved in nutrient acquisition by regulating root growth, nutrient uptake, and translocation, as well as the establishment of symbiosis with arbuscular mycorrhizas. Under nutrient stresses, PMAs are activated to pump more H+ and promote organic anion excretion, thus improving nutrient availability in the rhizosphere. Herein we review recent progress in the physiological functions and the underlying molecular mechanisms of PMAs in the efficient acquisition and utilization of various nutrients in plants. We also discuss perspectives for the application of PMAs in improving crop production and quality.

Identification of a major QTL and candidate genes analysis for branch angle in rapeseed (Brassica napus L.) using QTL-seq and RNA-seq

Introduction

Branching angle is an essential trait in determining the planting density of rapeseed (Brassica napus L.) and hence the yield per unit area. However, the mechanism of branching angle formation in rapeseed is not well understood.

Methods

In this study, two rapeseed germplasm with extreme branching angles were used to construct an F2 segregating population; then bulked segregant analysis sequencing (BSA-seq) and quantitative trait loci (QTL) mapping were utilized to localize branching anglerelated loci and combined with transcriptome sequencing (RNA-seq) and quantitative real-time PCR (qPCR) for candidate gene mining.

Results and discussion

A branching angle-associated quantitative trait loci (QTL) was mapped on chromosome C3 (C3: 1.54-2.65 Mb) by combining BSA-seq as well as traditional QTL mapping. A total of 54 genes had SNP/Indel variants within the QTL interval were identified. Further, RNA-seq of the two parents revealed that 12 of the 54 genes were differentially expressed between the two parents. Finally, we further validated the differentially expressed genes using qPCR and found that six of them presented consistent differential expression in all small branching angle samples and large branching angles, and thus were considered as candidate genes related to branching angles in rapeseed. Our results introduce new candidate genes for the regulation of branching angle formation in rapeseed, and provide an important reference for the subsequent exploration of its formation mechanism.

Phosphorylation of plasma membrane H+-ATPase Thr881 participates in light-induced stomatal opening

Plasma membrane (PM) H+-ATPase is crucial for light-induced stomatal opening and phosphorylation of a penultimate residue, Thr948 (pen-Thr, numbering according to Arabidopsis AHA1) is required for enzyme activation. In this study, a comprehensive phosphoproteomic analysis using guard cell protoplasts from Vicia faba shows that both red and blue light increase the phosphorylation of Thr881, of PM H+-ATPase. Light-induced stomatal opening and the blue light-induced increase in stomatal conductance are reduced in transgenic Arabidopsis plants expressing mutant AHA1-T881A in aha1-9, whereas the blue light-induced phosphorylation of pen-Thr is unaffected. Auxin and photosynthetically active radiation induce the phosphorylation of both Thr881 and pen-Thr in etiolated seedlings and leaves, respectively. The dephosphorylation of phosphorylated Thr881 and pen-Thr are mediated by type 2 C protein phosphatase clade D isoforms. Taken together, Thr881 phosphorylation, in addition of the pen-Thr phosphorylation, are important for PM H+-ATPase function during physiological responses, such as light-induced stomatal opening in Arabidopsis thaliana.

Exogenous auxin alters the polycyclic aromatic hydrocarbons apoplastic and symplastic uptake by wheat seedling roots

Polycyclic aromatic hydrocarbons (PAHs) are a category of organic pollutants known for their high carcinogenicity. Our previous research has illustrated that plant roots actively absorb PAHs through a co-transport mechanism with H+ ions. Because auxin can increase the H+-ATPase activity, the wheat roots were exposed to PAHs with/without auxins to study whether auxins facilitate the uptake of PAHs by plant roots and to gain insights into the underlying mechanisms of this process. In our study, indole acetic acid (100 μM) and α-naphthaleneacetic acid (10 μM) significantly increased the PAHs concentrations in apoplast and symplast, and the treating time and concentrations were positively correlated with PAHs accumulations. The time-dependent kinetics for 36 h followed the Elovich equation, and the concentration-dependent kinetics of apoplastic and symplastic uptake for 4 h could be described with the Freundlich and Michaelis-Menten equations, respectively. The proportion of PAHs accumulated in apoplast could be enhanced by auxins in most treatments. Our findings offer novel insights into the mechanisms of PAH uptake by plant roots under auxin exposure. Additionally, this research aids in refining strategies for ensuring crop safety and improving phytoremediation of PAH-contaminated soil and water.

The conserved evolution of plant H+-ATPase family and the involvement of soybean H+-ATPases in sodium bicarbonate stress responses

Plant plasma membrane (PM) H+-ATPases are essential pumps involved in multiple physiological processes. They play a significant role in regulating pH homeostasis and membrane potential by generating the electrochemical gradient of the proton across the plasma membrane. However, information on soybean PM H+-ATPase is still limited. In this study, we conducted the evolutionary analysis of PM H+-ATPases in land plants and investigated the subfamily classification and whole genome duplication of PM H+-ATPases in angiosperms. We further characterized the extremely high conservation of the soybean PM H+-ATPase family in terms of gene structure, domain architecture, and protein sequence identity. Using the yeast system, we confirmed the highly conserved biochemical characteristics (14-3-3 binding affinity and pump activity) of soybean PM H+-ATPases and their conserved function in enhancing tolerance to high pH and NaHCO3 stresses. Meanwhile, our results also revealed their divergence in the transcriptional expression in different tissues and under sodium bicarbonate stress. Finally, the function of soybean PM H+-ATPases in conferring sodium bicarbonate tolerance was validated using transgenic Arabidopsis. Together, these results conclude that the soybean PM H+-ATPase is evolutionarily conserved and positively regulates the response to sodium bicarbonate stress.

Physiological and transcriptome profiling of Chlorella sorokiniana: A study on azo dye wastewater decolorization

Over decades, synthetic dyes have become increasingly dominated by azo dyes posing a significant environmental risk due to their toxicity. Microalgae-based systems may offer an alternative for treatment of azo dye effluents to conventional physical-chemical methods. Here, microalgae were tested to decolorize industrial azo dye wastewater (ADW). Chlorella sorokiniana showed the highest decolorization efficiency in a preliminary screening test. Subsequently, the optimization of the experimental design resulted in 70% decolorization in a photobioreactor. Tolerance of this strain was evidenced using multiple approaches (growth and chlorophyll content assays, scanning electron microscopy (SEM), and antioxidant level measurements). Raman microspectroscopy was employed for the quantification of ADW-specific compounds accumulated by the microalgal biomass. Finally, RNA-seq revealed the transcriptome profile of C. sorokiniana exposed to ADW for 72 h. Activated DNA repair and primary metabolism provided sufficient energy for microalgal growth to overcome the adverse toxic conditions. Furthermore, several transporter genes, oxidoreductases-, and glycosyltransferases-encoding genes were upregulated to effectively sequestrate and detoxify the ADW. This work demonstrates the potential utilization of C. sorokiniana as a tolerant strain for industrial wastewater treatment, emphasizing the regulation of its molecular mechanisms to cope with unfavorable growth conditions.