Two trehalase isoforms,produced from a single transcript,regulate drought stress tolerance in Arabidopsis thaliana

Plant Molecular Biology - Alternative translation initiation of the unique Arabidopsis trehalase gene allows for the production of two isoforms with different subcellular localization, providing...     

Heterologous expression of the cysteine proteinase gene VaCP17 from the cold-adapted grapevine Vitis amurensis increases cold tolerance in Arabidopsis

Plant Cell, Tissue and Organ Culture (PCTOC) - Cysteine proteinases (thiol) carry out diverse and critical functions in plants through their ability to hydrolyze peptide bonds in target proteins....     

Cell-type-specific calcium responses to drought, salt and cold in the Arabidopsis root

Little is known about the signalling processes involved in the response of roots to abiotic stresses. The Arabidopsis root is a model system of root anatomy with a simple architecture and is amenable to genetic manipulation. Although it is known that the root responds to cold, drought and salt stress with increases in cytoplasmic free calcium, there is currently no information about the role(s) of the functionally diverse cell types that comprise the root. Transgenic Arabidopsis with enhancer-trapped GAL4 expression in specific cell types was used to target the calcium reporting protein, aequorin, fused to a modified yellow fluorescent protein (YFP). The luminescence output of targeted aequorin enabled in vivo measurement of changes in cytosolic free calcium concentrations ([Ca2+]cyt) in specific cell types during acute cold, osmotic and salt stresses. In response to an acute cold stress, all cell types tested as well as plants constitutively expressing aequorin displayed rapid [Ca2+]cyt peaks. However, there were significant quantitative differences between different cell types in terms of their response to cold stress, osmotic stress (440 mM mannitol) and salt stress (220 mM NaCl), implying specific roles for certain cell types in the detection and/or response to these stimuli. In response to osmotic and salt stress, the endodermis and pericycle displayed prolonged oscillations in cytosolic calcium that were distinct from the responses of the other cell types tested. Targeted expression of aequorin circumvented the technical difficulties involved in fluorescent dye injection as well as the lack of cell specificity of constitutively expressed aequorin, and revealed a new level of complexity in root calcium signalling.     

Costs and benefits of cold tolerance in transgenic Arabidopsis thaliana

Cold tolerance in plants is an ecologically important trait that has been under intensive study for basic and applied reasons. Determining the fitness benefits and costs of cold tolerance has previously been difficult because cold tolerance is normally an induced trait that is not expressed in warm environments. The recent creation of transgenic plants constitutively expressing cold tolerance genes enables the investigation of the fitness consequences of cold tolerance in multiple temperature environments. We studied three genes from the CBF (C-repeat/dehydration responsive element binding factor) cold tolerance pathway, CBF1, 2 and 3, in Arabidopsis thaliana to test for benefits and costs of constitutive cold tolerance. We used multiple insertion lines for each transgene and grew the lines in cold and control conditions. Costs of cold tolerance, as determined by fruit number, varied by individual transgene. CBF2 and 3 overexpressers showed costs of cold tolerance, and no fitness benefits, in both environments. CBF1 overexpressing plants showed no fitness cost of cold tolerance in the control environment and showed a marginal fitness benefit in the cold environment. These results suggest that constitutive expression of traits that are normally induced in response to environmental stress will not always lead to costs in the absence of that stress, and that the ecological risks of CBF transgene escape should be assessed prior to their use in commercial agriculture.     

Cystatin-like cysteine proteinase inhibitors from human liver.

Cysteine proteinase inhibitor (CPI) forms from human liver were purified from the tissue homogenate by alkaline denaturation of cysteine proteinases with which they are complexed, acetone fractionation, affinity chromatography on S-carboxymethyl-papain-Sepharose and chromatofocusing. The multiple forms of CPI were shown immunologically to be forms of two proteins, referred to as CPI-A (comprising the forms of relatively acidic pI) and CPI-B (comprising the more basic forms). CPI-A and CPI-B are similar in their Mr of about 12400, considerable stability to pH2, pH11 and 80 degrees C, and tight-binding inhibition of papain, several related cysteine proteinases and dipeptidyl peptidase I. Ki values were determined for papain, human cathepsins B, H and L, and dipeptidyl peptidase I. The affinity of CPI-A for cathepsin B was about 10-fold greater than that of CPI-B, whereas CBI-B showed about 100-fold stronger inhibition of dipeptidyl peptidase I. For all the cysteine proteinases the liver inhibitors were somewhat less tight binding than cystatin. The resemblance of both CPI-A and CPI-B in several respects to egg-white cystatin is discussed. CPI-A seems to correspond to the epithelial inhibitor described previously, and CPI-B to the inhibitor from other cell types [Järvinen & Rinne (1982) Biochim. Biophys. Acta 708, 210-217].     

Increased cysteine availability is essential for cadmium tolerance and accumulation in Arabidopsis thaliana

Employing genetic transformation using an Atcys-3A cDNA construct expressing the cytosolic O-acetylserine(thiol)lyase (OASTL), we obtained two Arabidopsis lines with different capabilities for supplying cysteine under metal stress conditions. Lines 1-2 and 10-10, grown under standard conditions, showed similar levels of cysteine and glutathione (GSH) to those of the wild-type. However, in the presence of cadmium, line 10-10 showed significantly higher levels. The increased thiol content allowed line 10-10 to survive under severe heavy metal stress conditions (up to 400 microm of cadmium in the growth medium), and resulted in an accumulation of cadmium in the leaves to a level similar to that of metal hyperaccumulator plants. Investigation of the epidermal leaf surface clearly showed that most of the cadmium had accumulated in the trichomes. Furthermore, line 10-10 was able to accumulate more cadmium in its trichomes than the wild-type, whereas line 1-2 showed a reduced capacity for cadmium accumulation. Our results suggest that an increased rate of cysteine biosynthesis is responsible for the enhanced cadmium tolerance and accumulation in trichome leaves. Thus, molecular engineering of the cysteine biosynthesis pathway, together with modification of the number of leaf trichomes, may have considerable potential in increasing heavy metal accumulation for phytoremediation purposes.     

Phytochrome B increases drought tolerance by enhancing ABA sensitivity in Arabidopsis thaliana

Phytochrome B (phyB) can adjust morphological and physiological responses according to changes in the red : far‐red (R:FR) ratio. phyB‐driven acclimation of plants to open environments (high R:FR ratio) increases carbon gain at the expense of increased water loss. This behaviour alleviates stressful conditions generated by an excess of light, but increases the chances of desiccation. Here we evaluated how phyB modulates this drought‐tolerance response by comparing wild‐type Arabidopsis thaliana adult plants to the null phyB in response to water shortage. phyB wilted before the wild type, and this was due to phyB maintaining open stomata under a reduction in soil water availability. Although phyB presented enhanced ABA levels under well‐watered conditions, this mutant was less sensitive than the wild type in diminishing stomatal conductance in response to exogenous ABA application. Reduced sensitivity to ABA in phyB correlated with a lower expression of ABCG22, which encodes a putative ABA influx transporter, and PYL5, which encodes a soluble ABA receptor. Furthermore, the expression of RAB18 and RD29A, both typical ABA‐induced genes, was lower in phyB than the wild type after ABA treatment. We propose that phyB contributes to the acclimation of plants to open environments by enhancing ABA sensitivity when soil water becomes limiting.     

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.     

Cloning and characterisation of a Primula heat shock protein gene, PfHSP17.1, which confers heat, salt and drought tolerance in transgenic Arabidopsis thaliana

Small heat shock proteins (sHSPs) are the critical components of responses to various environmental stresses. However, few have been functionally characterised in Primula. In this study, we cloned a sHSP gene, PfHSP17.1, which is highly up-regulated in the leaves of Primula forrestii exposed to thermal stress (42 °C for 2 h). Sequence alignment and phylogenetic analysis indicated that PfHSP17.1 is a member of the plant cytosolic class I sHSPs. This gene was basally and ubiquitously expressed in different plant organs. The expression of PfHSP17.1 was also triggered remarkably by salt, drought and oxidative stress conditions but was only slightly induced by abscisic acid. Transgenic Arabidopsis thaliana constitutively expressing PfHSP17.1 displayed increased thermotolerance and higher resistance to salt and drought compared with wild-type plants. These results highlight the important role that PfHSP17.1 plays in diverse physiological and biochemical processes related to adverse conditions.     

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...