The rice phosphoinositide-specific phospholipase C3 is involved in responses to osmotic stresses via modulating ROS homeostasis

AlgU mediates hyperosmotic tolerance in Pseudomonas protegens SN15-2 by regulating membrane stability, ROS scavenging, and osmolyte synthesis

Pseudomonas protegens can serve as an agricultural biocontrol agent. P. protegens often encounters hyperosmotic stress during industrial production and field application. The ability of P. protegens to withstand hyperosmotic stress is important for its application as a biocontrol agent. AlgU is a global regulator responsible for stress response and biocontrol ability. However, the specific regulatory role of AlgU in the hyperosmotic adaptation of P. protegens is poorly understood. In this study, we found that the AlgU mutation disrupted the hyperosmotic tolerance of P. protegens. Many genes and metabolites related to cell envelope formation were significantly downregulated in ΔalgU compared with that in the wild-type (WT) strain under hyperosmotic conditions, and we found that the algU mutation caused membrane integrity to be compromised and increased membrane permeability. Further experiments revealed that the cell envelope integrity protein TolA, which is regulated by AlgU, contributes to cell membrane stability and osmotic tolerance in P. protegens. In addition, several genes related to oxidative stress response were significantly downregulated in ΔalgU, and higher levels of intracellular reactive oxygen species were found in ΔalgU. Furthermore, we found that the synthesis of N-acetyl glutaminyl glutamine amide is directly regulated by AlgU and contributes to the hyperosmotic adaptation of P. protegens. This study revealed the mechanisms of AlgU's participation in osmotic tolerance in P. protegens, and it provides potential molecular targets for research on the hyperosmotic adaptation of P. protegens.IMPORTANCEIn this study, we found that the extracytoplasmic function sigma factor AlgU is essential for the survival of P. protegens under hyperosmotic conditions. We provided evidence supporting the roles of AlgU in influencing cell membrane stability, intracellular reactive oxygen species (ROS) accumulation, and dipeptide N-acetylglutaminylglutamine amide (NAGGN) synthesis in P. protegens under hyperosmotic conditions. Our findings revealed the mechanisms of AlgU's participation in hyperosmotic stress tolerance in P. protegens, and they provide potential molecular targets for research on the hyperosmotic adaptation of P. protegens, which is of value in improving the biocontrol ability of P. protegens.

Appropriate Drought Training Induces Optimal Drought Tolerance by Inducing Stepwise H2O2 Homeostasis in Soybean

Soybean is considered one of the most drought-sensitive crops, and ROS homeostasis can regulate drought tolerance in these plants. Understanding the mechanism of H2O2 homeostasis and its regulatory effect on drought stress is important for improving drought tolerance in soybean. We used different concentrations of polyethylene glycol (PEG) solutions to simulate the progression from weak drought stress (0.2%, 0.5%, and 1% PEG) to strong drought stress (5% PEG). We investigated the responses of the soybean plant phenotype, ROS level, injury severity, antioxidant system, etc., to different weak drought stresses and subsequent strong drought stresses. The results show that drought-treated plants accumulated H2O2 for signaling and exhibited drought tolerance under the following stronger drought stress, among which the 0.5% PEG treatment had the greatest effect. Under the optimal treatment, there was qualitatively describable H2O2 homeostasis, characterized by a consistent increasing amplitude in H2O2 content compared with CK. The H2O2 signal formed under the optimum treatment induced the capacity of the antioxidant system to remove excess H2O2 to form a primary H2O2 homeostasis. The primary H2O2 homeostasis further induced senior H2O2 homeostasis under the following strong drought and maximized the improvement of drought tolerance. These findings might suggest that gradual drought training could result in stepwise H2O2 homeostasis to continuously improve drought tolerance.

The F-Box/DUF295 Brassiceae specific 2 is involved in ABA-inhibited seed germination and seedling growth in Arabidopsis

To bear harsh environmental threats, plants have developed complex protection mechanisms involving phytohormones, counting abscisic acid (ABA). The function of the F-Box family containing the Domain of Unknown Function 295 (DUF295) has not yet been comprehensively characterized in Arabidopsis (Arabidopsis thaliana). In this study, we evaluated the function of a putative member of the F-Box/DUF295 family in Arabidopsis, F-box/DUF295 Brassiceae specific 2 (FDB2). We found that FDB2 expression was suppressed by ABA and abiotic stresses. FDB2 overexpression (OE) reduced ABA sensitivity during seed germination and seedling growth, but enhanced ABA-sensitivity of seed germination and seedling growth in fdb2 mutants was scored. When treated with ABA, expressions of ABI3, ABI4 and ABI5 showed decreased in OE lines but increased in fdb2 mutants. In addition, ABA-induced FDB2 degradation exhibited sensitive to MG132, suggesting that FDB2 degradation by ABA might be mediated by the ubiquitin-26S proteasome system. Moreover, ABA-induced significant over-accumulation of reactive oxygen species (ROS) at the root tips of fdb2 mutants was observed, this phenomenon was correlated to reduced activities of a set of ROS scavengers in fdb2 mutants relative to Col-0. In summary, our results suggest that Arabidopsis FDB2 is involved in ABA-mediated inhibition of seed germination, seedling growth including modulation of ROS homeostasis in roots.

The phosphoinositide-specific phospholipase C1 modulates flowering time and grain size in rice

Preferential expression of OsPLC1 is detected at the heading stage of rice, OsPLC1 overexpression results in early flowering, increased-grain size and yield; however, opposing phenotypes produced in the osplc1 mutants. Abstract: The importance of phospholipase C (PLC) in plant development has been demonstrated in several studies. OsPLC1, a member of PI-PLC in rice, although its role in the response to salt stress of rice seedlings has been reported, its functions in the growth and development of rice is elusive. Here, we report that OsPLC1 expression could be detectable in various tissues throughout the developmental stages of rice, and the highest expression level of OsPLC1 was detected at the heading stage. OsPLC1 overexpression (OE) produced rice plants with early flowering, whereas OsPLC1 loss-of-function led to delay in flowering. The expression levels of subset genes, which are involved in the control of flowering time in rice, were altered in the plants of OE and osplc1. In addition, the enlargement of grain size was observed in OE plants, however, the reduction of grain size was noticed in osplc1 mutants. The increase in the grain size and the grain yield of OE lines were associated with the improvement of cell length and expression levels of a set of genes related to cell expansion, contrarily, the decrease in osplc1 mutant grain size and yield were linked to declined cell length and expression levels of related genes. No significant differences, in terms of the grain quality of mature seeds, were found in OE and osplc1 mutants, with compared to those in Nipponbare (Nip). In summary, our study suggests that OsPLC1 could modulate rice flowering time and grain size.

Metabolomic Analysis Reveals Insights into Deterioration of Rice Quality during Storage

To determine the changes in the quality of rice during storage, this study investigated the comprehensive metabolomic profiles of Nanjing 9108 (typical japonica rice) and Jianzhen 2 (typical indica rice) varieties in China, using metabolomics. A total of 13 categories of 593 metabolites including lipids (134 species), phenolic acids (78 species), flavonoids (70 species), alkaloids (67 species), organic acids (64 species), amino acids and derivatives (64 species), saccharides and alcohols (44 species), nucleotides and derivatives (37 species), vitamins (14 species), lignans and coumarins (9 species), tannins (2 species), terpenoids (2 species), and others (8 species) were identified in both varieties. The result showed significant changes in 204 metabolites in Nanjing 9108, while only 26 were altered in Jianzhen 2 during storage. These metabolites involved 46 metabolic pathways. The TCA cycle, linoleic, and α-linolenic acid metabolic pathways were unique in Nanjing 9108. Finally, the results of quantitative mass spectrometry of 11 metabolites provided insight into biomarkers associated with quality deterioration of rice. This study provides insights into the mechanism of deterioration in the quality of rice during storage.