In grapevines, the MYB transcription factors play an important regulatory role in the phenylpropanoid pathway including proanthocyanidin, anthocyanin, and flavonoid biosynthesis. However, the role of MYB in abiotic stresses is not clear. In this study, an R2R3-MYB transcription factor, VyMYB24, was isolated from a high drought-tolerant Chinese wild Vitis species V. yanshanesis. Our findings demonstrated that it was involved in plant development and drought tolerance. VyMYB24 is a nuclear protein and is significantly induced by drought stress. When over-expressed in tobacco, VyMYB24 caused plant dwarfing including plant height, leaf area, flower size, and seed weight. The GA1+3 content in transgenic plants was reduced significantly, and spraying exogenous gibberellin could recover the dwarf phenotype of VyMYB24 transgenic plants, suggesting that VyMYB24 might inhibit plant development by the regulation of gibberellin (GA) metabolism. Under drought stress, the VyMYB24 transgenic plants improved their tolerance to drought with a lower wilting rate, lower relative electrical conductivity, and stronger roots. Compared to wild-type tobacco plants, VyMYB24 transgenic plants accumulated less reactive oxygen, accompanied by increased antioxidant enzyme activity and upregulated gene expression levels of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) genes. In addition, transgenic plants accumulated more proline, and their related synthetic genes NtP5CR and NtP5CS genes were significantly upregulated when exposed to drought. Besides, abiotic stress-responsive genes, NtDREB, NtERD10C, NtERD10D, and NtLEA5, were upregulated significantly in VyMYB24 transgenic plants. These results indicate that VyMYB24 plays a positive regulatory role in response to drought stress and also regulates plant development, which provides new evidence to further explore the molecular mechanism of drought stress of the MYB gene family.
BACKGROUND: HD-Zip genes encode several large and highly conserved protein families of transcription factors that play important roles in plant development and responses to environmental stress. To date, information about the involvement of HD-Zip in grape to drought response is limited. OBJECTIVE: The production of grapes is limited by a range of biotic and abiotic stresses, which cause significant losses in yield every year as well as a reduction in fruit quality. Identification and analysis of stress related genes in grapes are very important for cultivating more robust varieties with environmental stress resistance METHODS: We isolated a homeodomain-leucine zipper gene (HD-Zip), VvHDZ4, from grape, Vitis vinifera L. “Yatomi Rose”, and characterized VvHDZ4 based on analyses of its expression patterns, subcellular localization, transcription activity, and overexpression. RESULTS: We found that VvHDZ4 was highly expressed in roots and leaves, localized to nucleus, and activated the expression of reporter genes in yeast. The overexpression (OE) of VvHDZ4 led to enhanced drought stress tolerance in Solanum lycopersicum L. “Ailsa Craig” (tomato). The drought-tolerant phenotypes of the OE lines exhibited decreases in electrolyte leakage and rate of water loss, higher photosynthetic production and net photosynthesis rate, and showed up-regulation of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX), all of which are key antioxidant enzymes known to be activated during drought stress. Moreover, we observed the up-regulation of four additional drought stress indicator genes, SIDREB2A, SIAREB, SIRD29 and SIERD10, in the OE lines. VvHDZ4 improved drought tolerance in tomato, and the modes of action possibly consist of reducing membrane damage, increasing photosynthetic productivity, and modulating the expression of stress defense genes. CONCLUSIONS: This work increases our understanding of the important roles HD-Zip transcription factors in the responses of plants to the environment, especially abiotic stress.
Grape (Vitis vinifera) is among the world’s most important fruit crops and is a commonly used woody plant for genomics and post-genomics research. NAC transcription factors play central roles in plant growth and development, floral organ morphogenesis, and responses to biological stress. It is therefore important to identify key transcription factors from grape and clarify their mechanisms of action to generate genetic resources for grape molecular improvement. Our research group previously cloned a NAC transcription factor from V. vinifera ‘Yatomi Rosa’ [drought and leaf roll gene 1 (DRL1)] and demonstrated that it caused dwarfing of tobacco (Nicotiana benthamiana) plants when overexpressed. In the present work, we demonstrate that overexpression of DRL1 in transgenic tobacco delays flowering time and markedly reduces pollen viability. Furthermore, crosses between male DRL1 transgenic tobacco and female wild-type tobacco exhibit substantially lower fruit set, fruit and seed weights, fruit and seed shape indices, and seed germination rates than selfed wild-type plants or crosses with a transgenic female parent. DLR1 overexpression strongly influences flowering time and reproduction in transgenic tobacco, primarily through its effects on pollen development. These results provide a foundation for further functional characterization of DLR1 in grape.
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