Abiotic stresses, such as drought, salinity, extreme temperatures, chemical toxicity and oxidative stress are serious threats to agriculture and the natural status of the environment. Increased salinization of arable land is expected to have devastating global effects, resulting in 30% land loss within the next 25 years, and up to 50% by the year 2050. Therefore, breeding for drought and salinity stress tolerance in crop plants (for food supply) and in forest trees (a central component of the global ecosystem) should be given high research priority in plant biotechnology programs. Molecular control mechanisms for abiotic stress tolerance are based on the activation and regulation of specific stress-related genes. These genes are involved in the whole sequence of stress responses, such as signaling, transcriptional control, protection of membranes and proteins, and free-radical and toxic-compound scavenging. Recently, research into the molecular mechanisms of stress responses has started to bear fruit and, in parallel, genetic modification of stress tolerance has also shown promising results that may ultimately apply to agriculturally and ecologically important plants. The present review summarizes the recent advances in elucidating stress-response mechanisms and their biotechnological applications. Emphasis is placed on transgenic plants that have been engineered based on different stress-response mechanisms. The review examines the following aspects: regulatory controls, metabolite engineering, ion transport, antioxidants and detoxification, late embryogenesis abundant (LEA) and heat-shock proteins.

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Plant responses to drought, salinity and extreme temperatures: towards genetic engineering for stress tolerance

Plant growth and productivity are greatly affected by environmental stresses such as drought, high salinity, and low temperature. Expression of a variety of genes is induced by these stresses in various plants. The products of these genes function not only in stress tolerance but also in stress response. In the signal transduction network from perception of stress signals to stress-responsive gene expression, various transcription factors and cis-acting elements in the stress-responsive promoters function for plant adaptation to environmental stresses. Recent progress has been made in analyzing the complex cascades of gene expression in drought and cold stress responses, especially in identifying specificity and cross talk in stress signaling. In this review article, we highlight transcriptional regulation of gene expression in response to drought and cold stresses, with particular emphasis on the role of transcription factors and cis-acting elements in stress-inducible promoters.

Transcriptional regulatory networks in cellular responses and tolerance to dehydration and cold stresses.

https://www.cell.com/trends/plant-science/pdf/S1360-1385(07)00215-4.pdf

Cold stress regulation of gene expression in plants.

Cold temperatures trigger the expression of the CBF family of transcription factors, which in turn activate many downstream genes that confer chilling and freezing tolerance to plants. We report here the identification of ICE1 (inducer of CBF expression 1), an upstream transcription factor that regulates the transcription of CBF genes in the cold. An Arabidopsis ice1 mutant was isolated in a screen for mutations that impair cold-induced transcription of a CBF3 promoter-luciferase reporter gene. The ice1 mutation blocks the expression of CBF3 and decreases the expression of many genes downstream of CBFs, which leads to a significant reduction in plant chilling and freezing tolerance. ICE1 encodes a MYC-like bHLH transcriptional activator. ICE1 binds specifically to the MYC recognition sequences in the CBF3 promoter. ICE1 is expressed constitutively, and its overexpression in wild-type plants enhances the expression of the CBF regulon in the cold and improves freezing tolerance of the transgenic plants.

/pdf/ice1-a-regulator-of-cold-induced-transcriptome-and-freezing-5cd63j1o9w.pdf

ICE1: a regulator of cold-induced transcriptome and freezing tolerance in Arabidopsis

One-fifth of irrigated agriculture is adversely affected by soil salinity. Hence, developing salt-tolerant crops is essential for sustaining food production. Progress in breeding for salt-tolerant crops has been hampered by the lack of understanding of the molecular basis of salt tolerance and lack of availability of genes that confer salt tolerance. Genetic evidence suggests that perception of salt stress leads to a cytosolic calcium-signal that activates the calcium sensor protein SOS3. SOS3 binds to and activates a ser/thr protein kinase SOS2. The activated SOS2 kinase regulates activities of SOS1, a plasma membrane Na + /H + antiporter, and NHX1, a tonoplast Na + /H + anti-porter. This results in Na + efflux and vacuolar compartmentation. A putative osmosensory histidine kinase (AtHKI)-MAPK cascade probably regulates osmotic homeostasis and ROS scavenging. Osmotic stress and ABA (abscisic acid)-mediated regulation of LEA (late-embryogenesis-abundant)-type proteins also play important roles in plant salt tolerance. Genetic engineering of ion transporters and their regulators, and of the CBF (C-repeat-binding factor) regulons, holds promise for future development of salt-tolerant crops.

Understanding and Improving Salt Tolerance in Plants

In an attempt to improve stress tolerance of tomato (Lycopersicon esculentum) plants, an expression vector containing an Arabidopsis C-repeat/dehydration responsive element binding factor 1 (CBF1) cDNA driven by a cauliflower mosaic virus 35S promoter was transferred into tomato plants. Transgenic expression of CBF1 was proved by northern- and western-blot analyses. The degree of chilling tolerance of transgenic T1 and T2 plants was found to be significantly greater than that of wild-type tomato plants as measured by survival rate, chlorophyll fluorescence value, and radical elongation. The transgenic tomato plants exhibited patterns of growth retardation; however, they resumed normal growth after GA3 (gibberellic acid) treatment. More importantly, GA3-treated transgenic plants still exhibited a greater degree of chilling tolerance compared with wild-type plants. Subtractive hybridization was performed to isolate the responsive genes of heterologous Arabidopsis CBF1 in transgenic tomato plants. CATALASE1 (CAT1) was obtained and showed activation in transgenic tomato plants. The CAT1 gene and catalase activity were also highly induced in the transgenic tomato plants. The level of H2O2 in the transgenic plants was lower than that in the wild-type plants under either normal or cold conditions. The transgenic plants also exhibited considerable tolerance against oxidative damage induced by methyl viologen. Results from the current study suggest that heterologous CBF1 expression in transgenic tomato plants may induce several oxidative-stress responsive genes to protect from chilling stress.

Heterology expression of the Arabidopsis C-repeat/dehydration response element binding factor 1 gene confers elevated tolerance to chilling and oxidative stresses in transgenic tomato.

Erratum: Heterology expression of the Arabidopsis C-repeat/dehydration response element binding factor 1 gene confers elevated tolerance to chilling and oxidative stresses in transgenic tomato (Plant Physiology (2002) 129 (1086-1094))

Jent Turn Lee

Papers

Heterology expression of the Arabidopsis C-repeat/dehydration response element binding factor 1 gene confers elevated tolerance to chilling and oxidative stresses in transgenic tomato.

Erratum: Heterology expression of the Arabidopsis C-repeat/dehydration response element binding factor 1 gene confers elevated tolerance to chilling and oxidative stresses in transgenic tomato (Plant Physiology (2002) 129 (1086-1094))