SOS5 gene-abscisic acid crosstalk and their interaction with antioxidant system in Arabidopsis thaliana under salt stress

Functional identification of DNA demethylase gene CaROS1 in pepper (Capsicum annuum L.) involved in salt stress

Pepper, which is a widely cultivated important vegetable, is sensitive to salt stress, and the continuous intensification of soil salinization has affected pepper production worldwide. However, genes confer to salt tolerance are rarely been cloned in pepper. Since the REPRESSOR OF SILENCING 1 (ROS1) is a DNA demethylase that plays a crucial regulatory role in plants in response to various abiotic stresses, including salt stress. We cloned a ROS1 gene in pepper, named CaROS1 (LOC107843637). Bioinformatic analysis showed that the CaROS1 protein contains the HhH-GPD glycosylase and RRM_DME domains. qRT-PCR analyses showed that the CaROS1 was highly expressed in young and mature fruits of pepper and rapidly induced by salt stress. Functional characterization of the CaROS1 was performed by gene silencing in pepper and overexpressing in tobacco, revealed that the CaROS1 positively regulates salt tolerance ability. More detailly, CaROS1-silenced pepper were more sensitive to salt stress, and their ROS levels, relative conductivity, and malondialdehyde content were significantly higher in leaves than those of the control plants. Besides, CaROS1-overexpressing tobacco plants were more tolerant to salt stress, with a higher relative water content, total chlorophyll content, and antioxidant enzyme activity in leaves compared to those of WT plants during salt stress. These results revealed the CaROS1 dose play a role in salt stress response, providing the theoretical basis for salt tolerance genetic engineering breeding in pepper.

Salinity-Induced Physiochemical Alterations to Enhance Lipid Content in Oleaginous Microalgae Scenedesmus sp. BHU1 via Two-Stage Cultivation for Biodiesel Feedstock

In the recent past, various microalgae have been considered a renewable energy source for biofuel production, and their amount and extent can be enhanced by applying certain types of stress including salinity. Although microalgae growing under salinity stress result in a higher lipid content, they simultaneously reduce in growth and biomass output. To resolve this issue, the physiochemical changes in microalgae Scenedesmus sp. BHU1 have been assessed through two-stage cultivation. In stage-I, the maximum carbohydrate and lipid contents (39.55 and 34.10%) were found at a 0.4 M NaCl concentration, while in stage-II, the maximum carbohydrate and lipid contents (42.16 and 38.10%) were obtained in the 8-day-old culture. However, under increased salinity, Scenedesmus sp. BHU1 exhibited a decrease in photosynthetic attributes, including Chl-a, Chl-b, Fv/Fm, Y(II), Y(NPQ), NPQ, qP, qL, qN, and ETRmax but increased Y(NO) and carotenoids content. Apart from physiological attributes, osmoprotectants, stress biomarkers, and nonenzymatic antioxidants were also studied to elucidate the role of reactive oxygen species (ROS) facilitated lipid synthesis. Furthermore, elemental and mineral ion analysis of microalgal biomass was performed to evaluate the biomass quality for biofuel and cell homeostasis. Based on fluorometry analysis, we found the maximum neutral lipids in the 8-day-old grown culture at stage-II in Scenedesmus sp. BHU1. Furthermore, the use of Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy analyses confirmed the presence of higher levels of hydrocarbons and triacylglycerides (TAGs) composed of saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs) in the 8-day-old culture. Therefore, Scenedesmus sp. BHU1 can be a promising microalga for potential biodiesel feedstock.

Response of Prolyl 4 Hydroxylases, Arabinogalactan Proteins and Homogalacturonans in Four Olive Cultivars under Long-Term Salinity Stress in Relation to Physiological and Morphological Changes

Olive (Olea europeae L.) salinity stress induces responses at morphological, physiological and molecular levels, affecting plant productivity. Four olive cultivars with differential tolerance to salt were grown under saline conditions in long barrels for regular root growth to mimic field conditions. Arvanitolia and Lefkolia were previously reported as tolerant to salinity, and Koroneiki and Gaidourelia were characterized as sensitive, exhibiting a decrease in leaf length and leaf area index after 90 days of salinity. Prolyl 4-hydroxylases (P4Hs) hydroxylate cell wall glycoproteins such as arabinogalactan proteins (AGPs). The expression patterns of P4Hs and AGPs under saline conditions showed cultivar-dependent differences in leaves and roots. In the tolerant cultivars, no changes in OeP4H and OeAGP mRNAs were observed, while in the sensitive cultivars, the majority of OeP4Hs and OeAGPs were upregulated in leaves. Immunodetection showed that the AGP signal intensity and the cortical cell size, shape and intercellular spaces under saline conditions were similar to the control in Arvanitolia, while in Koroneiki, a weak AGP signal was associated with irregular cells and intercellular spaces, leading to aerenchyma formation after 45 days of NaCl treatment. Moreover, the acceleration of endodermal development and the formation of exodermal and cortical cells with thickened cell walls were observed, and an overall decrease in the abundance of cell wall homogalacturonans was detected in salt-treated roots. In conclusion, Arvanitolia and Lefkolia exhibited the highest adaptive capacity to salinity, indicating that their use as rootstocks might provide increased tolerance to irrigation with saline water.

The regulation of the cell wall by glycosylphosphatidylinositol-anchored proteins in Arabidopsis

A polysaccharides-based cell wall covers the plant cell, shaping it and protecting it from the harsh environment. Cellulose microfibrils constitute the cell wall backbone and are embedded in a matrix of pectic and hemicellulosic polysaccharides and glycoproteins. Various environmental and developmental cues can regulate the plant cell wall, and diverse glycosylphosphatidylinositol (GPI)-anchored proteins participate in these regulations. GPI is a common lipid modification on eukaryotic proteins, which covalently tethers the proteins to the membrane lipid bilayer. Catalyzed by a series of enzymic complexes, protein precursors are post-translationally modified at their hydrophobic carboxyl-terminus in the endomembrane system and anchored to the lipid bilayer through an oligosaccharidic GPI modification. Ultimately, mature proteins reach the plasma membrane via the secretory pathway facing toward the apoplast and cell wall in plants. In Arabidopsis, more than three hundred GPI-anchored proteins (GPI-APs) have been predicted, and many are reported to be involved in diverse regulations of the cell wall. In this review, we summarize GPI-APs involved in cell wall regulation. GPI-APs are proposed to act as structural components of the cell wall, organize cellulose microfibrils at the cell surface, and during cell wall integrity signaling transduction. Besides regulating protein trafficking, the GPI modification is potentially governed by a GPI shedding system that cleaves and releases the GPI-anchored proteins from the plasma membrane into the cell wall.

How salt stress-responsive proteins regulate plant adaptation to saline conditions

An overview is presented of recent advances in our knowledge of candidate proteins that regulate various physiological and biochemical processes underpinning plant adaptation to saline conditions. Salt stress is one of the environmental constraints that restrict plant distribution, growth and yield in many parts of the world. Increased world population surely elevates food demands all over the globe, which anticipates to add a great challenge to humanity. These concerns have necessitated the scientists to understand and unmask the puzzle of plant salt tolerance mechanisms in order to utilize various strategies to develop salt tolerant crop plants. Salt tolerance is a complex trait involving alterations in physiological, biochemical, and molecular processes. These alterations are a result of genomic and proteomic complement readjustments that lead to tolerance mechanisms. Proteomics is a crucial molecular tool that indicates proteins expressed by the genome, and also identifies the functions of proteins accumulated in response to salt stress. Recently, proteomic studies have shed more light on a range of promising candidate proteins that regulate various processes rendering salt tolerance to plants. These proteins have been shown to be involved in photosynthesis and energy metabolism, ion homeostasis, gene transcription and protein biosynthesis, compatible solute production, hormone modulation, cell wall structure modification, cellular detoxification, membrane stabilization, and signal transduction. These candidate salt responsive proteins can be therefore used in biotechnological approaches to improve tolerance of crop plants to salt conditions. In this review, we provided comprehensive updated information on the proteomic data of plants/genotypes contrasting in salt tolerance in response to salt stress. The roles of salt responsive proteins that are potential determinants for plant salt adaptation are discussed. The relationship between changes in proteome composition and abundance, and alterations observed in physiological and biochemical features associated with salt tolerance are also addressed.

Salt induced oxidative stress alters physiological, biochemical and metabolomic responses of green microalga Chlamydomonas reinhardtii

Salinity is one of the most significant environmental factors limiting microalgal biomass productivity. In the present study, the model microalga Chlamydomonas reinhardtii (C. reinhardtii) was exposed to 200 mM NaCl for eight days to explore the physiological, biochemical and metabolomic changes. C. reinhradtii exhibited a significant decrease in growth rate, and Chl a and Chl b levels. 200 mM NaCl induced ROS generation in C. reinhardtii with increase in H2O2 content. This caused lipid peroxidation with increase in MDA levels. C. reinhardtii also exhibited an increase in carbohydrate and lipid accumulation under 200 mM NaCl conditions as storage molecules in cells to maintain microalgal survival. In addition, NaCl stress increased the content of carotenoids, polyphenols and osmoprotectant molecules such as proline. SOD and APX activities decreased, while ROS-scavenger enzymes (POD and CAT) decreased. Metabolomic response showed an accumulation of the major molecules implicated in membrane remodelling and stress resistance such oleic acid (40.29%), linolenic acid (19.29%), alkanes, alkenes and phytosterols. The present study indicates the physiological, biochemical and metabolomic responses of C. reinhardtii to salt stress.

The antioxidant defense and glyoxalase systems contribute to the thermotolerance of Heliotropium thermophilum

This study focused on the impact of the antioxidant defence and glyoxalase systems on extreme heat tolerance of the thermophilic plant Heliotropium thermophilum L. For this purpose, plants were exposed to 20, 40, 60 and 80±5°C soil temperature gradually for 15days under laboratory conditions. Our results showed that the hydrogen peroxide and superoxide levels of H. thermophilum were lower at 40±5°C and higher at 80±5°C compared with plants grown at 20±5°C. Some antioxidant enzyme activities tended to increase in plants at 40, 60 and 80±5°C compared with those at 20±5°C and the protein contents responsible for the antioxidant enzymes were in parallel with these enzyme activities. The contents of both reduced and oxidised ascorbate and glutathione rose with increasing temperature. Methylglyoxal level was lower at 40±5°C and higher at 80±5°C compared with plants grown at 20±5°C. Glyoxalase activities highly increased with rising of soil temperature from 20±5°C to 80±5°C. The results of this study suggest that differential modulations of enzymatic antioxidants and the increase in non-enzymatic antioxidants and glyoxalase activities can contribute to the development of the thermotolerance of H. thermophilum through the detoxification of reactive oxygen species and methylglyoxal.

The FLA4-FEI Pathway: A Unique and Mysterious Signaling Module Related to Cell Wall Structure and Stress Signaling

Cell wall integrity control in plants involves multiple signaling modules that are mostly defined by genetic interactions. The putative co-receptors FEI1 and FEI2 and the extracellular glycoprotein FLA4 present the core components of a signaling pathway that acts in response to environmental conditions and insults to cell wall structure to modulate the balance of various growth regulators and, ultimately, to regulate the performance of the primary cell wall. Although the previously established genetic interactions are presently not matched by intermolecular binding studies, numerous receptor-like molecules that were identified in genome-wide interaction studies potentially contribute to the signaling machinery around the FLA4-FEI core. Apart from its function throughout the model plant Arabidopsis thaliana for the homeostasis of growth and stress responses, the FLA4-FEI pathway might support important agronomic traits in crop plants.

Arabinogalactan Proteins in Plant Roots - An Update on Possible Functions

Responsiveness to environmental conditions and developmental plasticity of root systems are crucial determinants of plant fitness. These processes are interconnected at a cellular level with cell wall properties and cell surface signaling, which involve arabinogalactan proteins (AGPs) as essential components. AGPs are cell-wall localized glycoproteins, often GPI-anchored, which participate in root functions at many levels. They are involved in cell expansion and differentiation, regulation of root growth, interactions with other organisms, and environmental response. Due to the complexity of cell wall functional and regulatory networks, and despite the large amount of experimental data, the exact molecular mechanisms of AGP-action are still largely unknown. This dynamically evolving field of root biology is summarized in the present review.