Diverse roles of jasmonates and ethylene in abiotic stress tolerance.

MYB Transcription Factors as Regulators of Phenylpropanoid Metabolism in Plants

Cranberries (Vaccinium macrocarpon Ait.) are an excellent dietary source of phytochemicals that include flavonol glycosides, anthocyanins, proanthocyanidins (condensed tannins), and organic and phenolic acids. Using C-18 and Sephadex Lipophilic LH-20 column chromatography, HPLC and tandem LC-ES/MS, we have analyzed, quantified and separated total cranberry extract (TCE) into fractions enriched in sugars, organic acids, total polyphenols, proanthocyanidins and anthocyanins (39.4, 30.0, 10.6, 5.5, 1.2% composition, respectively). Using a luminescent ATP cell viability assay, the antiproliferative effects of TCE (200 g/mL) vs. all fractions were evaluated against human oral (KB, CAL27), colon (HT-29, HCT116, SW480, SW620) and prostate (RWPE-1, RWPE-2, 22Rv1) cancer cell lines. The total polyphenol fraction was the most active fraction against all cell lines with 96.1 and 95% inhibition of KB and CAL27 oral cancer cells, respectively. For the colon cancer cells, the antiproliferative activity of this fraction was greatest against HCT116 (92.1%) than HT-29 (61.1%), SW480 (60%) and SW620 (63%). TCE and all fractions, showed 50% antiproliferative activity against prostate cancer cells with total polyphenols being the most active fraction (RWPE-1, 95%; RWPE-2, 95%; 22Rv1, 99.6%). Cranberry sugars (78.8 g/mL) did not inhibit the proliferation of any cancer cell lines. The enhanced antiproliferative activity of total polyphenols compared to TCE and its individual phytochemicals suggests synergistic or additive antiproliferative interactions of the anthocyanins, proanthocyanidins and flavonol glycosides within the cranberry extract.

Total Cranberry Extract vs. its Phytochemical Constituents: Antiproliferative and Synergistic Effects against Human Tumor Cell Lines

Agricultural production and quality are adversely affected by various abiotic stresses worldwide and this will be exacerbated by the deterioration of global climate. To feed a growing world population, it is very urgent to breed stress-tolerant crops with higher yields and improved qualities against multiple environmental stresses. Since conventional breeding approaches had marginal success due to the complexity of stress tolerance traits, the transgenic approach is now being popularly used to breed stress-tolerant crops. So identifying and characterizing the critical genes involved in plant stress responses is an essential prerequisite for engineering stress-tolerant crops. Far beyond the manipulation of single functional gene, engineering certain regulatory genes has emerged as an effective strategy now for controlling the expression of many stress-responsive genes. Transcription factors (TFs) are good candidates for genetic engineering to breed stress-tolerant crop because of their role as master regulators of many stress-responsive genes. Many TFs belonging to families AP2/EREBP, MYB, WRKY, NAC, bZIP have been found to be involved in various abiotic stresses and some TF genes have also been engineered to improve stress tolerance in model and crop plants. In this review, we take five large families of TFs as examples and review the recent progress of TFs involved in plant abiotic stress responses and their potential utilization to improve multiple stress tolerance of crops in the field conditions.

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Recent Advances in Utilizing Transcription Factors to Improve Plant Abiotic Stress Tolerance by Transgenic Technology

Water scarcity is one of the major causes of poor plant performance and limited crop yields worldwide and it is the single most common cause of severe food shortage in developing countries. Several molecular networks involved in stress perception, signal transduction and stress responses in plants have been elucidated so far. Transcription factors are major players in water stress signaling. In recent years, different MYB transcription factors, mainly in Arabidopsis thaliana (L.) Heynh. but also in some crops, have been characterized for their involvement in drought response. For some of them there is evidence supporting a specific role in response to water stress, such as the regulation of stomatal movement, the control of suberin and cuticular waxes synthesis and the regulation of flower development. Moreover, some of these genes have also been characterized for their involvement in other abiotic or biotic stresses, an important feature considering that in nature, plants are often simultaneously subjected to multiple rather than single environmental perturbations. This review summarizes recent studies highlighting the role of the MYB family of transcription factors in the adaptive responses to drought stress. The practical application value of MYBs in crop improvement, such as stress tolerance engineering, is also discussed.

Plant MYB Transcription Factors: Their Role in Drought Response Mechanisms.

Isolation and molecular characterization of GmERF7, a soybean ethylene-response factor that increases salt stress tolerance in tobacco.

A novel MYB transcription factor, GmMYBJ1, from soybean confers drought and cold tolerance in Arabidopsis thaliana.

A R2R3-MYB transcription factor, GmMYB12B2, affects the expression levels of flavonoid biosynthesis genes encoding key enzymes in transgenic Arabidopsis plants.

Transformation is one of the fundamental and essential molecular cloning techniques. In this paper, we have reported a modified method for preparation and transformation of competent cells. This modified method, improved from a classical protocol, has made some modifications on the concentration of calcium chloride and competent bacteria solution, rotation speed in centrifugation and centrifugation time. It was found that the optimal transformation efficiency were obtained when the concentration of CaCl 2 was 75 mmol/l, OD 600 of the culture meets 0.35 to 0.45, the temperature of rotation was 4°C , rotation speed was 1000 g and rotation time was 5 min. Even more, we also found out that the transformation efficiency would increase about 10 to 30 times when adding 15% glycerine into CaCl 2  solution. The transformation efficiency, using our new method, reaches 10 8 cf u/μg and higher than ultra-competent Escherichia coli method. This method will improve the efficiency in the molecular cloning and the construction of gene library. Keywords: Competent cells, CaCl 2 , improved method, transformation, glycerine, transformation efficiency

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An improved calcium chloride method preparation and transformation of competent cells

MYB genes are extensively distributed in higher plants and constitute one of the largest transcription factors (TFs) families. These TFs have been proved to be implicated in the regulation of plant growth, development, metabolism, and multiple abiotic stress responses. In the present study, a new soybean MYB gene, denoted GmMYBJ2, was isolated and its function was characterized. The GmMYBJ2 cDNA is 1428 bp in length with an open reading frame (ORF) of 960 bp encoding 319 amino acids. Sequence and yeast one-hybrid analyses showed GmMYBJ2 contains two MYB domains and belongs to R2R3-MYB protein with transactivation activity. Transient expression analysis using the GmMYBJ2-GFP fusion gene in onion epidermal cells showed GmMYBJ2 protein is targeted to the nucleus. GmMYBJ2 was induced by drought, cold, salt, and exogenous abscisic acid (ABA). Arabidopsis overexpressing GmMYBJ2 exhibited a higher seed germination rates (GRs), a notable increase in the soluble sugar content under water-deficit stress, and a lower water loss rate (WLR) when water is sufficient. These results indicated the overexpression of GmMYBJ2 make transgenic Arabidopsis more tolerant to drought stress than wild-type (WT) plants, and GmMYBJ2 may be useful for improving drought stress tolerance in transgenic plant breeding.

Qing-Yu Wang

Papers

Isolation and molecular characterization of GmERF7, a soybean ethylene-response factor that increases salt stress tolerance in tobacco.

A novel MYB transcription factor, GmMYBJ1, from soybean confers drought and cold tolerance in Arabidopsis thaliana.

A R2R3-MYB transcription factor, GmMYB12B2, affects the expression levels of flavonoid biosynthesis genes encoding key enzymes in transgenic Arabidopsis plants.

An improved calcium chloride method preparation and transformation of competent cells

The soybean gene, GmMYBJ2, encodes a R2R3-type transcription factor involved in drought stress tolerance in Arabidopsis thaliana