Plants cope with aluminum (Al) toxicity by secreting organic acids (OAs) into the apoplastic space, which is driven by proton (H 1) pumps. Here, we show that mutation of vacuolar H 1-translocating adenosine triphosphatase (H 1-ATPase) subunit a2 (VHA-a2) and VHA-a3 of the vacuolar H 1-ATPase enhances Al resistance in Arabidopsis (Arabidopsis thaliana). vha-a2 vha-a3 mutant plants displayed less Al sensitivity with less Al accumulation in roots compared to wild-type plants when grown under excessive Al 31. Interestingly, in response to Al 31 exposure, plants showed decreased vacuolar H 1 pump activity and reduced expression of VHA-a2 and VHA-a3, which were accompanied by increased plasma membrane H 1 pump (PM H 1-ATPase) activity. Genetic analysis of plants with altered PM H 1-ATPase activity established a correlation between Al-induced increase in PM H 1-ATPase activity and enhanced Al resistance in vha-a2 vha-a3 plants. We determined that external OAs, such as malate and citrate whose secretion is driven by PM H 1-ATPase, increased with PM H 1-ATPase activity upon Al stress. On the other hand, elevated secretion of malate and citrate in vha-a2 vha-a3 root exudates appeared to be independent of OAs metabolism and tolerance of phosphate starvation but was likely related to impaired vacuolar sequestration. These results suggest that coordination of vacuolar H 1-ATPase and PM H 1-ATPase dictates the distribution of OAs into either the vacuolar lumen or the apoplastic space that, in turn, determines Al tolerance capacity in plants.

Type 2C protein phosphatases (PP2Cs) are the largest protein phosphatase family. PP2Cs dephosphorylate substrates for signaling in Arabidopsis, but the functions of most PP2Cs remain unknown. Here, we characterized PP2C49 (AT3G62260, a Group G PP2C), which regulates Na+ distribution under salt stress and is localized to the cytoplasm and nucleus. PP2C49 was highly expressed in root vascular tissues and its disruption enhanced plant tolerance to salt stress. Compared with wild type, the pp2c49 mutant contained more Na+ in roots but less Na+ in shoots and xylem sap, suggesting that PP2C49 regulates shoot Na+ extrusion. Reciprocal grafting revealed a root‐based mechanism underlying the salt tolerance of pp2c49. Systemic Na+ distribution largely depends on AtHKT1;1 and loss of function of AtHKT1;1 in the pp2c49 background overrode the salt tolerance of pp2c49, resulting in salt sensitivity. Furthermore, compared with plants overexpressing PP2C49 in the wild‐type background, plants overexpressing PP2C49 in the athtk1;1 mutant background were sensitive to salt, like the athtk1;1 mutants. Moreover, protein–protein interaction and two‐voltage clamping assays demonstrated that PP2C49 physically interacts with AtHKT1;1 and inhibits the Na+ permeability of AtHKT1;1. This study reveals that PP2C49 negatively regulates AtHKT1;1 activity and thus determines systemic Na+ allocation during salt stress.

Phytophthora capsici is a broad-host-range oomycete pathogen, which can cause severe phytophthora blight disease of pepper and hundreds of other plant species worldwide. Natural resistance against P. capsici is inadequate, and it is very difficult to control by most of existing chemical fungicides. Therefore, it is urgent demand to develop alternative strategies to control this pathogen. Recently, host-induced or spray-induced gene silencing of pathogen’s essential or virulent genes provided an effective strategy for disease controls. Here, we demonstrated that P. capsici could effectively take up siRNAs from environment. According to RNA-seq and qRT-PCR analysis, we identified four P. capsici RXLR effector genes that are significantly up-regulated during the infection stage. Transient over-expression and promote infection assays indicated that RXLR1 and RXLR4 could promote the pathogen’s infection. Using VIGS system in pepper plants, we found that in planta expressing RNAi construct that target RXLR1 or RXLR4 could significantly reduce the pathogen’s infection, while co-interfering RXLR1 and RXLR4 could confer a more enhanced resistance to P. capsici. We also found that exogenous applying siRNAs that target RXLR1 or RXLR4 could restrict growth of P. capsici on the pepper and Nicotiana benthamiana leaves; when targeting RXLR1 and RXLR4 simultaneously, the control effect was more remarkable. These data suggested that RNAi-based gene silencing of RXLR effectors has great potential for application in crop improvement against P. capsici and also provides an important basis for the development of RNA-based anti-oomycete agents.

Nitrate (NO 3 −) is a source of plant nutrients and osmolytes, but its delivery machineries under osmotic and low-nutrient stress remain largely unknown. Here, we report that AtICln, an Arabidopsis homolog of the nucleotide-sensitive chloride-conductance regulatory protein family (ICln), is involved in response to osmotic and low-NO 3 − stress. The gene AtICln, encoding plasma membrane-anchored proteins, was upregulated by various osmotic stresses, and its disruption impaired plant tolerance to osmotic stress. Compared with the wild type, the aticln mutant retained lower anions, particularly NO 3 − , and its growth retardation was not rescued by NO 3 − supply under osmotic stress. Interestingly, this mutant also displayed growth defects under low-NO 3 stress, which were accompanied by decreases in NO 3 − accumulation, suggesting that AtICln may facilitate the NO 3 − accumulation under NO 3 − deficiency. Moreover, the low-NO 3 − hypersensitive phenotype of aticln mutant was overridden by the overexpression of NRT1.1, an important NO 3 − transporter in Arabidopsis low-NO 3 − responses. Further genetic analysis in the plants with altered activity of AtICln and NRT1.1 indicated that AtICln and NRT1.1 play a compensatory role in maintaining NO 3 − homeostasis under low-NO 3 − environments.These results suggest that AtICln is involved in cellular NO 3 − accumulation and thus determines osmotic adjustment and low-NO 3 − tolerance in plants.