Plants respond with changes in their pattern of gene expression and protein products when exposed to low tem- peratures. Thus ability to adapt has an impact on the distribution and survival of the plant, and on crop yields. Many spe- cies of tropical or subtropical origin are injured or killed by non-freezing low temperatures, and exhibit various symptoms of chilling injury such as chlorosis, necrosis, or growth retardation. In contrast, chilling tolerant species are able to grow at such cold temperatures. Conventional breeding methods have met with limited success in improving the cold tolerance of important crop plants involving inter-specific or inter-generic hybridization. Recent studies involving full genome profil- ing/sequencing, mutational and transgenic plant analyses, have provided a deep insight of the complex transcriptional mechanism that operates under cold stress. The alterations in expression of genes in response to cold temperatures are fol- lowed by increases in the levels of hundreds of metabolites, some of which are known to have protective effects against the damaging effects of cold stress. Various low temperature inducible genes have been isolated from plants. Most appear to be involved in tolerance to cold stress and the expression of some of them is regulated by C-repeat binding fac- tor/dehydration-responsive element binding (CBF/DREB1) transcription factors. Numerous physiological and molecular changes occur during cold acclimation which reveals that the cold resistance is more complex than perceived and involves more than one pathway. The findings summarized in this review have shown potential practical applications for breeding cold tolerance in crop and horticultural plants suitable to temperate geographical locations.

/pdf/engineering-cold-stress-tolerance-in-crop-plants-cgfeviyc5o.pdf

Engineering Cold Stress Tolerance in Crop Plants

Plants, algae, and photosynthetic bacteria experience frequent changes in environment. The ability to survive depends on their capacity to acclimate to such changes. In particular, fluctuations in temperature affect the fluidity of cytoplasmic and thylakoid membranes. The molecular mechanisms responsible for the perception of changes in membrane fluidity have not been fully characterized. However, the understanding of the functions of the individual genes for fatty acid desaturases in cyanobacteria and plants led to the directed mutagenesis of such genes that altered the membrane fluidity of cytoplasmic and thylakoid membranes. Characterization of the photosynthetic properties of the transformed cyanobacteria and higher plants revealed that lipid unsaturation is essential for protection of the photosynthetic machinery against environmental stresses, such as strong light, salt stress, and high and low temperatures. The unsaturation of fatty acids enhances the repair of the damaged photosystem II complex under stress conditions. In this review, we summarize the knowledge on the mechanisms that regulate membrane fluidity, on putative sensors that perceive changes in membrane fluidity, on genes that are involved in acclimation to new sets of environmental conditions, and on the influence of membrane properties on photosynthetic functions.

Regulatory role of membrane fluidity in gene expression and physiological functions

Multiple biotic and abiotic environmental stress factors affect negatively various aspects of plant growth, development, and crop productivity. Plants, as sessile organisms, have developed, in the course of their evolution, efficient strategies of response to avoid, tolerate, or adapt to different types of stress situations. The diverse stress factors that plants have to face often activate similar cell signaling pathways and cellular responses, such as the production of stress proteins, upregulation of the antioxidant machinery, and accumulation of compatible solutes. Over the last few decades advances in plant physiology, genetics, and molecular biology have greatly improved our understanding of plant responses to abiotic stress conditions. In this paper, recent progresses on systematic analyses of plant responses to stress including genomics, proteomics, metabolomics, and transgenic-based approaches are summarized.

/pdf/biotechnological-approaches-to-study-plant-responses-to-4ckltq49v6.pdf

Biotechnological approaches to study plant responses to stress.

Modern agricultural crop production relies on the growth of a few of the world's plant species selected for their superior qualities and suitability as food, animal feed, fiber or industrial end uses. Centuries of selection and, more recently, scientific breeding for adaptation to biotic and abiotic stresses have been necessary to improve yield, yield stability, and product quality in agricultural species.

https://www.springer.com/cda/content/document/cda_downloaddocument/9783642048111-c1.pdf?SGWID=0-0-45-925843-p173937306

Transgenic Plants for Abiotic Stress Resistance

A tomato (Lycopersicon esculentum Mill.) monodehydroascorbate reductase gene (LeMDAR) was isolated. The LeMDAR-green fluorescence protein (GFP) fusion protein was targeted to chloroplast in Arabidopsis mesophyll protoplast. RNA and protein gel blot analyses confirmed that the sense- and antisense- LeMDAR were integrated into the tomato genome. The MDAR activities and the levels of reduced ascorbate (AsA) were markedly increased in sense transgenic lines and decreased in antisense transgenic lines compared with wild-type (WT) plants. Under low and high temperature stresses, the sense transgenic plants showed lower level of hydrogen peroxide (H(2)O(2)), lower thiobarbituric acid reactive substance (TBARS) content, higher net photosynthetic rate (P(n)), higher maximal photochemical efficiency of PSII (F(v)/F(m)) and fresh weight compared with WT plants. The oxidizable P700 decreased more obviously in WT and antisense plants than that in sense plants at chilling temperature under low irradiance. Furthermore, the sense transgenic plants exhibited significantly lower H(2)O(2) level, higher ascorbate peroxidase (APX) activity, greater P(n) and F(v)/F(m) under methyl viologen (MV)-mediated oxidative stresses. These results indicated that overexpression of chloroplastic MDAR played an important role in alleviating photoinhibition of PSI and PSII and enhancing the tolerance to various abiotic stresses by elevating AsA level.

Overexpression of chloroplastic monodehydroascorbate reductase enhanced tolerance to temperature and methyl viologen-mediated oxidative stresses

A tomato (Lycopersicon esculentum Mill.) glycerol-3-phosphate acyltransferase gene (LeGPAT) was isolated. The deduced amino acid sequence revealed that LeGPAT contained four acyltransferase domains, showing high identities with GPAT in other plant species. A GFP fusion protein of LeGPAT was targeted to chloroplast in cowpea mesophyll protoplast. RNA gel blot showed that the mRNA accumulation of LeGPAT in the wild type (WT) was induced by chilling temperature. Higher expression levels were observed when tomato leaves were exposed to 4°C for 4 h. RNA gel and western blot analysis confirmed that the sense gene LeGPAT was transferred into the tomato genome and overexpressed under the control of 35S-CaMV. Although tomato is classified as a chilling-sensitive plant, LeGPAT exhibited selectivity to 18:1 over 16:0. Overexpression of LeGPAT increased total activity of LeGPAT and cis-unsaturated fatty acids in PG in thylakoid membrane. Chilling treatment induced less ion leakage from the transgenic plants than from the WT. The photosynthetic rate and the maximal photochemical efficiency of PS II (Fv/Fm) in transgenic plants decreased more slowly during chilling stress and recovered faster than in WT under optimal conditions. The oxidizable P700 in both WT and transgenic plants decreased obviously at chilling temperature under low irradiance, but the oxidizable P700 recovered faster in transgenic plants than in the WT. These results indicate that overexpression of LeGPAT increased the levels of PG cis-unsaturated fatty acids in thylakoid membrane, which was beneficial for the recovery of chilling-induced PS I photoinhibition in tomato.

Overexpression of glycerol-3-phosphate acyltransferase gene improves chilling tolerance in tomato.

A chloroplast-localized tomato (Lycopersicon esculentum Mill.) glycerol-3-phosphate acyltransferase (LeGPAT) gene was isolated. The antisense tomato plants were got under the control of the caulifower mosaic virus 35S promoter (35S-CaMV). RNA gel blot analysis confirmed that the expression of LeGPAT was inhibited in the tomato genome. The depletion of LeGPAT caused a massive arrest in pollen development. It also increased the size of tapetal cells, delayed tapetum degeneration, reduced ER membrane biogenesis and altered oil body size. Results therefore suggested that LeGPAT played a crucial role in pollen development. There was, however, no effect on the ovule. The depletion of LeGPAT also increased the saturation of phosphatidylglycerol (PG) fatty acids in thylakoid membranes. Increase of PG-saturated fatty acids was helpful in alleviating photoinhibition of PSII in tomato plants under heat stress.

Shi-Jie Zhao

Papers

Overexpression of glycerol-3-phosphate acyltransferase gene improves chilling tolerance in tomato.

Antisense-mediated depletion of tomato chloroplast glycerol-3-phosphate acyltransferase affects male fertility and increases thermal tolerance

Photosynthetic Characteristics of a Super High Yield Cultivar of Winter Wheat During Late Growth Period