Genes encoding chitinase-antifreeze proteins are regulated by cold and expressed by all cell types in winter rye shoots.
ABSTRACT One group of antifreeze proteins (AFPs) is composed of two chitinases that accumulate in the apoplast of winter rye leaves during cold acclimation. In this study, the 28- and 35-kDa chitinase-AFPs were localized in nonacclimated and cold-acclimated rye leaves by immunoelectron microscopy with an antiserum produced against the purified winter rye 35-kDa chitinase-AFP. In cold-acclimated winter rye leaves, labelled chitinase-AFPs were abundant in the walls of epidermal, parenchymal sheath and mesophyll cells and xylem vessels, while less label was present in walls of vascular parenchyma cells. In contrast, chitinase labelling was essentially absent in the nonacclimated cells except in xylem vessels. As shown by RNA blotting, the transcripts of chitinase-AFPs accumulated to a high level in rye leaves during cold acclimation, to a lesser extent in crowns and were not detectable in roots. mRNA transcripts of the 28-kDa chitinase-AFP were localized in rye leaves by in situ hybridization. The chitinase-AFP transcripts were found in the same cell types as the protein itself. We conclude that all metabolically active cell types in cold-acclimated winter rye leaves and crowns are able to synthesize chitinase-AFPs and secrete them into adjacent cell walls, where they may interact with ice to delay its propagation through the plant and modify its growth.
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ABSTRACT: Cold signals interact with other environmental cues to modulate plant developmental processes. Recent studies have shown that many Pathogenesis-Related (PR) genes are induced and disease resistance is enhanced after exposure to low temperatures, linking cold signals with pathogenesis in plants. However, the underlying molecular mechanisms and signaling schemes are largely unknown. Here, we demonstrate that cold stimulates proteolytic activation of a plasma membrane-tethered NAC (NAM/ATAF1/2/CUC2) transcription factor NTL6. The transcriptionally active NTL6 protein enters the nucleus, where it induces a subset of PR genes by directly binding to a conserved sequence in the promoters of cold-responsive PR genes, such as PR1, PR2, and PR5. While transgenic plants overexpressing an active NTL6 form exhibited enhanced disease resistance, RNAi plants with reduced NTL6 activity were more susceptible to pathogen infection at low temperatures. Accordingly, cold induction of PR1 disappeared in the RNAi plants. Consistent with the close relationship between cold and pathogenesis, cold-acclimated plants showed enhanced resistance to pathogen infection. In this signaling cascade, controlled activation of the membrane-tethered, dormant NTL6 transcription factor serves as a molecular link that incorporates cold signals into pathogen resistance responses. However, the NTL6-mediated cold induction of the PR genes is independent of salicylic acid (SA). The PR genes were still induced by SA in the NTL6 RNAi plants. Cold regulation of the PR genes through the membrane-mediated transcriptional control is thought to be an adaptive process that ensures quick plant responses to incoming pathogens that frequently occur during cold seasons.The Plant Journal 11/2009; 61(4):661-71. · 6.58 Impact Factor
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ABSTRACT: Plants are constantly exposed to a variety of environmental stresses. Freezing or extremely low temperature constitutes a key factor influencing plant growth, development and crop productivity. Plants have evolved a mechanism to enhance tolerance to freezing during exposure to periods of low, but non-freezing temperatures. This phenomenon is called cold acclimation. During cold acclimation, plants develop several mechanisms to minimize potential damages caused by low temperature. Cold response is highly complex process that involves an array of physiological and biochemical modifications. Furthermore, alterations of the expression patterns of many genes, proteins and metabolites in response to cold stress have been reported. Recent studies demonstrate that post-transcriptional and post-translational regulations play a role in the regulation of cold signaling. In this review article, recent advances in cold stress signaling and tolerance are highlighted.International Journal of Molecular Sciences 01/2013; 14(3):5312-37. · 2.46 Impact Factor
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ABSTRACT: Antifreeze proteins depress the non-equilibrium freezing point of aqueous solutions, but only have a small effect on the equilibrium melting point. This difference between the freezing and melting points has been termed thermal hysteresis activity (THA). THA identifies the presence and relative activity of antifreeze proteins. Two antifreeze protein cDNAs, dafp-1 and dafp-4, encoding two self-enhancing (have a synergistic effect on THA) antifreeze proteins (DAFPs) from the beetle Dendroides canadensis, were introduced into the genome of Arabidopsis thaliana via Agrobacterium-mediated floral dip transformation. Southern blot analysis indicated multiple insertions of transgenes. Both DAFP-1 and/or DAFP-4 were expressed in transgenic A. thaliana as shown by RT-PCR and Western blot. Apoplastic fluid from T 3 DAFP-1 + DAFP-4-producing transgenic A. thaliana exhibited THA in the range of 1.2–1.35°C (using the capillary method to determine THA), demonstrating the presence of functioning antifreeze proteins (with signal peptides for extracellular secretion). The freezing temperature of DAFP-1 + DAFP-4-producing transgenic A. thaliana was lowered by approximately 2–3°C compared with the wild type.Plant Molecular Biology Reporter 01/2011; · 5.32 Impact Factor