A novel calmodulin-binding protein functions as a negative regulator of osmotic stress tolerance in Arabidopsis thaliana seedlings

A clone for a novel Arabidopsisthaliana calmodulin (CaM)-binding protein of 25 kDa (AtCaMBP25) has been isolated by using a radiolabelled CaM probe to screen a cDNA expression library derived from A. thaliana cell suspension cultures challenged with osmotic stress. The deduced amino acid sequence of AtCaMBP25 contains putative nuclear localization sequences and shares significant degree of similarity with hypothetical plant proteins only. Fusion of the AtCaMBP25 coding sequence to reporter genes targets the hybrid protein to the nucleus. Bacterially expressed AtCaMBP25 binds, in a calcium-dependent manner, to a canonical CaM but not to a less conserved isoform of the calcium sensor. AtCaMBP25 is encoded by a single-copy gene, whose expression is induced in Arabidopsis seedlings exposed to dehydration, low temperature or high salinity. Transgenic plants overexpressing AtCaMBP25 exhibits an increased sensitivity to both ionic (NaCl) and non-ionic (mannitol) osmotic stress during seed germination and seedling growth. By contrast, transgenic lines expressing antisense AtCaMBP25 are significantly more tolerant to mannitol and NaCl stresses than the wild type. Thus, the AtCaMBP25 gene functions as a negative effector of osmotic stress tolerance and likely participates in stress signal transduction pathways.     

Methods and concepts in quantifying resistance to drought, salt and freezing, abiotic stresses that affect plant water status

The abiotic stresses of drought, salinity and freezing are linked by the fact that they all decrease the availability of water to plant cells. This decreased availability of water is quantified as a decrease in water potential. Plants resist low water potential and related stresses by modifying water uptake and loss to avoid low water potential, accumulating solutes and modifying the properties of cell walls to avoid the dehydration induced by low water potential and using protective proteins and mechanisms to tolerate reduced water content by preventing or repairing cell damage. Salt stress also alters plant ion homeostasis, and under many conditions this may be the predominant factor affecting plant performance. Our emphasis is on experiments that quantify resistance to realistic and reproducible low water potential (drought), salt and freezing stresses while being suitable for genetic studies where a large number of lines must be analyzed. Detailed protocols for the use of polyethylene glycol-infused agar plates to impose low water potential stress, assay of salt tolerance based on root elongation, quantification of freezing tolerance and the use of electrolyte leakage experiments to quantify cellular damage induced by freezing and low water potential are also presented.     

Zinc-finger protein GmZF351 improves both salt and drought stress tolerance in soybean

Abiotic stress is one of the most important factors reducing soybean yield. It is essential to identify regulatory factors contributing to stress responses.A previous study found that the tandem CCCH zincfinger protein Gm ZF351 is an oil level regulator. In this study, we discovered that the Gm ZF351 gene is induced by stress and that the overexpression of Gm ZF351 confers stress tolerance to transgenic soybean. Gm ZF351 directly regulates the expression of Gm CIPK9 and Gm SnRK, leading to stoma...     

ALS3 encodes a phloem-localized ABC transporter-like protein that is required for aluminum tolerance in Arabidopsis

Aluminum (Al) toxicity in acid soils is a worldwide agricultural problem that severely limits crop productivity through inhibition of root growth. Previously, Arabidopsis mutants with increased Al sensitivity were isolated in order to identify genes important for Al tolerance in plants. One mutant, als3, exhibited extreme root growth inhibition in the presence of Al, suggesting that this mutation negatively impacts a gene required for Al tolerance. Map-based cloning of the als3-1 mutation resulted in the isolation of a novel gene that encodes a previously undescribed ABC transporter-like protein, which is highly homologous to a putative bacterial metal resistance protein, ybbM. Northern analysis for ALS3 expression revealed that it is found in all organs examined, which is consistent with the global nature of Al sensitivity displayed by als3, and that expression increases in roots following Al treatment. Based on GUS fusion and in situ hybridization analyses, ALS3 is primarily expressed in leaf hydathodes and the phloem throughout the plant, along with the root cortex following Al treatment. Immunolocalization indicates that ALS3 predominantly accumulates in the plasma membrane of cells that express ALS3. From our results, it appears that ALS3 encodes an ABC transporter-like protein that is required for Al resistance/tolerance and may function to redistribute accumulated Al away from sensitive tissues in order to protect the growing root from the toxic effects of Al.     

Pre-conditioning the epigenetic response to high vapor pressure deficit increases the drought tolerance of Arabidopsis thaliana

Epigenetic modification of the genome via cytosine methylation is a dynamic process that responds to changes in the growing environment. This modification can also be heritable. The combination of both properties means that there is the potential for the life experiences of the parental generation to modify the methylation profiles of their offspring and so potentially to “pre-condition” them to better accommodate abiotic conditions encountered by their parents. We recently identified high vapor pressure deficit (vpd)-induced DNA methylation at 2 gene loci in the stomatal development pathway and an associated reduction in leaf stomatal frequency.¹ Here, we test whether this epigenetic modification pre-conditioned parents and their offspring to the more severe water stress of periodic drought. We found that 3 generations of high vpd-grown plants were better able to withstand periodic drought stress over 2 generations. This resistance was not directly associated with de novo methylation of the target stomata genes, but was associated with the cmt3 mutant’s inability to maintain asymmetric sequence context methylation. If our finding applies widely, it could have significant implications for evolutionary biology and breeding for stressful environments.     

The Arabidopsis UDP‐glycosyltransferases UGT79B2 and UGT79B3, contribute to cold,salt and drought stress tolerance via modulating anthocyanin accumulation

The plant family 1 UDP‐glycosyltransferases (UGTs) are the biggest GT family in plants, which are responsible for transferring sugar moieties onto a variety of small molecules, and control many metabolic processes; however, their physiological significance in planta is largely unknown. Here, we revealed that two Arabidopsis glycosyltransferase genes, UGT79B2 and UGT79B3, could be strongly induced by various abiotic stresses, including cold, salt and drought stresses. Overexpression of UGT79B2/B3 significantly enhanced plant tolerance to low temperatures as well as drought and salt stresses, whereas the ugt79b2/b3 double mutants generated by RNAi (RNA interference) and CRISPR‐Cas9 strategies were more susceptible to adverse conditions. Interestingly, the expression of UGT79B2 and UGT79B3 is directly controlled by CBF1 (CRT/DRE‐binding factor 1, also named DREB1B) in response to low temperatures. Furthermore, we identified the enzyme activities of UGT79B2/B3 in adding UDP‐rhamnose to cyanidin and cyanidin 3‐O‐glucoside. Ectopic expression of UGT79B2/B3 significantly increased the anthocyanin accumulation, and enhanced the antioxidant activity in coping with abiotic stresses, whereas the ugt79b2/b3 double mutants showed reduced anthocyanin levels. When overexpressing UGT79B2/B3 in tt18 (transparent testa 18), a mutant that cannot synthesize anthocyanins, both genes fail to improve plant adaptation to stress. Taken together, we demonstrate that UGT79B2 and UGT79B3, identified as anthocyanin rhamnosyltransferases, are regulated by CBF1 and confer abiotic stress tolerance via modulating anthocyanin accumulation.     

Molecular genetics of heat tolerance and heat shock proteins in cereals

Heat stress is common in most cereal-growing areas of the world. In this paper, we summarize the current knowledge on the molecular and genetic basis of thermotolerance in vegetative and reproductive tissues of cereals. Significance of heat stress response and expression of heat shock proteins (HSPs) in thermotolerance of cereal yield and quality is discussed. Major avenues for increasing thermotolerance in cereals via conventional breeding or genetic modification are outlined.     

A cellulose synthase‐like protein is required for osmotic stress tolerance in Arabidopsis

Osmotic stress imposed by soil salinity and drought stress significantly affects plant growth and development, but osmotic stress sensing and tolerance mechanisms are not well understood. Forward genetic screens using a root‐bending assay have previously identified salt overly sensitive (sos) mutants of Arabidopsis that fall into five loci, SOS1 to SOS5. These loci are required for the regulation of ion homeostasis or cell expansion under salt stress, but do not play a major role in plant tolerance to the osmotic stress component of soil salinity or drought. Here we report an additional sos mutant, sos6‐1, which defines a locus essential for osmotic stress tolerance. sos6‐1 plants are hypersensitive to salt stress and osmotic stress imposed by mannitol or polyethylene glycol in culture media or by water deficit in the soil. SOS6 encodes a cellulose synthase‐like protein, AtCSLD5. Only modest differences in cell wall chemical composition could be detected, but we found that sos6‐1 mutant plants accumulate high levels of reactive oxygen species (ROS) under osmotic stress and are hypersensitive to the oxidative stress reagent methyl viologen. The results suggest that SOS6/AtCSLD5 is not required for normal plant growth and development but has a critical role in osmotic stress tolerance and this function likely involves its regulation of ROS under stress.     

Decreased capacity for sodium export out of Arabidopsis chloroplasts impairs salt tolerance,photosynthesis and plant performance

Salt stress is a widespread phenomenon, limiting plant performance in large areas around the world. Although various types of plant sodium/proton antiporters have been characterized, the physiological function of NHD1 from Arabidopsis thaliana has not been elucidated in detail so far. Here we report that the NHD1–GFP fusion protein localizes to the chloroplast envelope. Heterologous expression of AtNHD1 was sufficient to complement a salt‐sensitive Escherichia coli mutant lacking its endogenous sodium/proton exchangers. Transport competence of NHD1 was confirmed using recombinant, highly purified carrier protein reconstituted into proteoliposomes, proving Na⁺/H⁺ antiport. In planta NHD1 expression was found to be highest in mature and senescent leaves but was not induced by sodium chloride application. When compared to wild‐type controls, nhd1 T–DNA insertion mutants showed decreased biomasses and lower chlorophyll levels after sodium feeding. Interestingly, if grown on sand and supplemented with high sodium chloride, nhd1 mutants exhibited leaf tissue Na⁺ levels similar to those of wild‐type plants, but the Na⁺ content of chloroplasts increased significantly. These high sodium levels in mutant chloroplasts resulted in markedly impaired photosynthetic performance as revealed by a lower quantum yield of photosystem II and increased non‐photochemical quenching. Moreover, high Na⁺ levels might hamper activity of the plastidic bile acid/sodium symporter family protein 2 (BASS2). The resulting pyruvate deficiency might cause the observed decreased phenylalanine levels in the nhd1 mutants due to lack of precursors.     

An RNA chaperone,AtCSP2, negatively regulates salt stress tolerance

Cold shock domain (CSD) proteins are RNA chaperones that destabilize RNA secondary structures. Arabidopsis Cold Shock Domain Protein 2 (AtCSP2), one of the 4 CSD proteins (AtCSP1-AtCSP4) in Arabidopsis, is induced during cold acclimation but negatively regulates freezing tolerance. Here, we analyzed the function of AtCSP2 in salt stress tolerance. A double mutant, with reduced AtCSP2 and no AtCSP4 expression (atcsp2–3 atcsp4–1), displayed higher survival rates after salt stress. In addition, overexpression of AtCSP2 resulted in reduced salt stress tolerance. These data demonstrate that AtCSP2 acts as a negative regulator of salt stress tolerance in Arabidopsis.     

A B-box zinc finger protein,MdBBX10, enhanced salt and drought stresses tolerance in Arabidopsis

Plant Molecular Biology - The expression of MdBBX10 was significantly induced by different stresses and ABA treatments. Overexpression of MdBBX10 in Arabidopsis significantly enhanced abiotic...     

Biostimulants enhance growth and drought tolerance in Arabidopsis thaliana and exhibit chemical priming action

The usage of biostimulants in agriculture has been steadily increasing in recent years, and their benefits have been recognised by growers. The growing interest from industry has led to a boom in the number of products on the market, many of which are derived from a diverse range of sources such as microbials, plant extracts, hydrolysed amino acids and algal extracts. However, there has been a slower recognition of the biostimulant sector by the scientific community. This has been a result of limited fundamental research into the modes of action of many biostimulant products and the speed at which new multi‐compound products have entered the market. In this study, we have developed a readily reproducible bioassay using the model plant Arabidopsis thaliana to test biostimulant efficacy under drought conditions and assess any chemical priming action. We have screened three products with biostimulant action derived from amino acids (Delfan Plus), Ascophyllum nodosum extract (Phylgreen) or potassium phosphite (Trafos K). Under a progressive soil drought condition, we measured changes in plant growth, biochemical content and gene expression levels. Our results demonstrated biostimulant‐mediated drought tolerance, with the products requiring different application timings for successful stress mitigation. The analysis of the biochemical and gene expression changes provided evidence of chemical priming action when plants were pre‐treated with biostimulants prior to the drought stress exposure.