Dorota Konopka-Postupolska

The Role of Annexin 1 in Drought Stress in Arabidopsis

Annexins act as targets of calcium signals in eukaryotic cells, and recent results suggest that they play an important role in plant stress responses. We found that in Arabidopsis (Arabidopsis thaliana), AnnAt1 (for annexin 1) mRNA levels were up-regulated in leaves by most of the stress treatments applied. Plants overexpressing AnnAt1 protein were more drought tolerant and knockout plants were more drought sensitive than ecotype Columbia plants. We also observed that hydrogen peroxide accumulation in guard cells was reduced in overexpressing plants and increased in knockout plants both before and after treatment with abscisic acid. Oxidative protection resulting from AnnAt1 overexpression could be due to the low level of intrinsic peroxidase activity exhibited by this protein in vitro, previously linked to a conserved histidine residue found in a peroxidase-like motif. However, analyses of a mutant H40A AnnAt1 protein in a bacterial complementation test and in peroxidase activity assays indicate that this residue is not critical to the ability of AnnAt1 to confer oxidative protection. To further examine the mechanism(s) linking AnnAt1 expression to stress resistance, we analyzed the reactive S3 cluster to determine if it plays a role in AnnAt1 oligomerization and/or is the site for posttranslational modification. We found that the two cysteine residues in this cluster do not form intramolecular or intermolecular bonds but are highly susceptible to oxidation-driven S-glutathionylation, which decreases the Ca2+ affinity of AnnAt1 in vitro. Moreover, S-glutathionylation of AnnAt1 occurs in planta after abscisic acid treatment, which suggests that this modification could be important in regulating the cellular function of AnnAt1 during stress responses.

Structure, function and membrane interactions of plant annexins: an update.

Knowledge accumulated over the past 15 years on plant annexins clearly indicates that this disparate group of proteins builds on the common annexin function of membrane association, but possesses divergent molecular mechanisms. Functionally, the current literature agrees on a key role of plant annexins in stress response processes such as wound healing and drought tolerance. This is contrasted by only few established details of the molecular level mechanisms that are driving these activities. In this review, we appraise the current knowledge of plant annexin molecular, functional and structural properties with a special emphasis on topics of less coverage in recent past overviews. In particular, plant annexin post-translational modification, roles in polar growth and membrane stabilisation processes are discussed.

Role of polyisoprenoids in tobacco resistance against biotic stresses

Infection with avirulent pathogens, tobacco mosaic virus (TMV) or Pseudomonas syringae pv. tabaci induced accumulation of polyisoprenoid alcohols, solanesol and a family of polyprenols [from polyprenol composed of 14 isoprene units (Pren-14) to -18, with Pren-16 dominating] in the leaves of resistant tobacco plants Nicotiana tabacum cv. Samsun NN. Upon TMV infection, solanesol content was increased seven- and eight-fold in the inoculated and upper leaves, respectively, while polyprenol content was increased 2.5- and 2-fold in the inoculated and upper leaves, respectively, on the seventh day post-infection. Accumulation of polyisoprenoid alcohols was also stimulated by exogenously applied hydrogen peroxide but not by exogenous salicylic acid (SA). On the contrary, neither inoculation of the leaves of susceptible tobacco plants nor wounding of tobacco leaves caused an increase in polyisoprenoid content. Taken together, these results indicate that polyisoprenoid alcohols might be involved in plant resistance against pathogens. A putative role of accumulated polyisoprenoids in plant response to pathogen attack is discussed. Similarly, the content of plastoquinone (PQ) was increased two-fold in TMV-inoculated and upper leaves of resistant plants. Accumulation of PQ was also stimulated by hydrogen peroxide, bacteria (P. syringae) and SA. The role of PQ in antioxidant defense in cellular membranous compartments is discussed in the context of the enzymatic antioxidant machinery activated in tobacco leaves subjected to viral infection. Elevated activity of several antioxidant enzymes (ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and superoxide dismutase, especially the CuZn superoxide dismutase isoform) and high, but transient elevation of catalase was found in inoculated leaves of resistant tobacco plants but not in susceptible plants.

Down‐regulation of CBP80 gene expression as a strategy to engineer a drought‐tolerant potato

Developing new strategies for crop plants to respond to drought is crucial for their innovative breeding. The down-regulation of nuclear cap-binding proteins in Arabidopsis renders plants drought tolerant. The CBP80 gene in the potato cultivar Desiree was silenced using artificial microRNAs. Transgenic plants displayed a higher tolerance to drought, ABA-hypersensitive stomatal closing, an increase in leaf stomata and trichome density, and compact cuticle structures with a lower number of microchannels. These findings were correlated with a higher tolerance to water stress. The level of miR159 was decreased, and the levels of its target mRNAs MYB33 and MYB101 increased in the transgenic plants subjected to drought. Similar trends were observed in an Arabidopsis cbp80 mutant. The evolutionary conservation of CBP80, a gene that plays a role in the response to drought, suggests that it is a candidate for genetic manipulations that aim to obtain improved water-deficit tolerance of crop plants.

Is annexin 1 a multifunctional protein during stress responses

Accumulating evidence suggest that certain annexins can play a role in abiotic stress responses in plants. We found that for one member of the Arabidopsis annexin gene family, annexin 1 (AnnAt1), loss-of-function mutants are more sensitive to drought stress and gain-of-function mutants are more tolerant1. We also found that AnnAt1 is able to regulate accumulation of H2O2 in vivo in Arabidopsis cells based on the observation that the level of ROS accumulation following induction by ABA correlates with the level of AnnAt1 protein in transgenic Arabidopsis plants. Here we provide more commentary on the antioxidant activity of AnnAt1, critically assess the evidence that AnnAt1 and other annexins possess peroxidase activity, emphasize a redox-induced post-translational modification which occurs to AnnAt1 during ABA signaling, and discuss ways this annexin’s membrane associations could mediate stress signaling while addressing the potential that AnnAt1 is a multifunctional protein in plants.

Potato Annexin STANN1 Promotes Drought Tolerance and Mitigates Light Stress in Transgenic Solanum tuberosum L. Plants.

Annexins are a family of calcium- and membrane-binding proteins that are important for plant tolerance to adverse environmental conditions. Annexins function to counteract oxidative stress, maintain cell redox homeostasis, and enhance drought tolerance. In the present study, an endogenous annexin, STANN1, was overexpressed to determine whether crop yields could be improved in potato (Solanum tuberosum L.) during drought. Nine potential potato annexins were identified and their expression characterized in response to drought treatment. STANN1 mRNA was constitutively expressed at a high level and drought treatment strongly increased transcription levels. Therefore, STANN1 was selected for overexpression analysis. Under drought conditions, transgenic potato plants ectopically expressing STANN1 were more tolerant to water deficit in the root zone, preserved more water in green tissues, maintained chloroplast functions, and had higher accumulation of chlorophyll b and xanthophylls (especially zeaxanthin) than wild type (WT). Drought-induced reductions in the maximum efficiency and the electron transport rate of photosystem II (PSII), as well as the quantum yield of photosynthesis, were less pronounced in transgenic plants overexpressing STANN1 than in the WT. This conferred more efficient non-photochemical energy dissipation in the outer antennae of PSII and probably more efficient protection of reaction centers against photooxidative damage in transgenic plants under drought conditions. Consequently, these plants were able to maintain effective photosynthesis during drought, which resulted in greater productivity than WT plants despite water scarcity. Although the mechanisms underlying this stress protection are not yet clear, annexin-mediated photoprotection is probably linked to protection against light-induced oxidative stress.

Annexins as Overlooked Regulators of Membrane Trafficking in Plant Cells

Annexins are an evolutionary conserved superfamily of proteins able to bind membrane phospholipids in a calcium-dependent manner. Their physiological roles are still being intensively examined and it seems that, despite their general structural similarity, individual proteins are specialized toward specific functions. However, due to their general ability to coordinate membranes in a calcium-sensitive fashion they are thought to participate in membrane flow. In this review, we present a summary of the current understanding of cellular transport in plant cells and consider the possible roles of annexins in different stages of vesicular transport.

Collagenase as a useful tool for the analysis of plant cellular peripheries.

A technique for the selective loosening of the cell wall structure and the isolation of proteins permanently knotted in the cell walls was elaborated. Following treatment with collagenase, some proteins, such as calreticulin (CRT) and auxin binding protein 1 (ABP1) were released from purified cell walls, most probably through destruction of respective interacting proteins. The results were confirmed by the immunolocalization of the ABP1 and CRT with confocal and electron microscopy. On the other hand, potential substrates of collagenase, among them annexin 1 have been recognized. Mass spectra of annexin 1 obtained after collagenase digestion and results from analysis of potential cleavage sites suggested that the mechanism of enzyme cleavage might not depend on the amino acid sequence. Summarizing, collagenase was found to be a very useful tool for exploring molecules involved in the functioning of cellular peripheries.