Responses of soybean to cold temperature / Dehydrins in Arabidopsis and soybean

Yuji Yamasaki, Purdue University

Abstract

Abiotic stresses such as cold, drought, osmotic, and salinity are serious environmental problems for plants. Exposure to stresses can lead to the decline of free water, ion imbalance, lipid peroxidation, and loss of enzyme function, all of which influence metabolic activities. Cold tolerant plants, such as Arabidopsis, are able to acclimate and thus survive in sustained or more severe stress conditions. In the cold acclimation process, specific transcription factors are accumulated to induce the expression of genes that increase cold stress tolerance. Most members of DREB1/CBF family are cold responsive transcription factors in vegetative tissues. CBF 1-3 are ABA-independent, cold-specific transcription factors that are strongly accumulated within the first one hour after cold exposure. They induce the expression of cold-regulated genes such as dehydrins, which are known to contribute to cold tolerance. The goal of this project is to understand the role of dehydrins in stress tolerance in Arabidopsis (a cold tolerant plant) and begin to understand the reasons why soybean is not cold tolerant. To reach to this goal, 4 main aims were developed: 1) to characterize the functional role of Arabidopsis dehydrins through tissue localization of two acidic dehydrins, AtERD14 and AtQ9T022; and a phenotypic analysis of the basic dehydrin, AtXERO1, 2) to identify and characterize soybean dehydrins, 3) to identify and test the functionality of soybean CBF genes, and 4) to evaluate the correlation between fatty acid composition and cold imbibition tolerance in seeds of domesticated and wild soybean lines. AtERD14 was found to be expressed primarily in vegetative vascular tissue and in early stages of embryo development. AtQ9T022 expression was localized in meristems during early seed development and was found only in meristem tissues after germination. These two genes thus seemed unlikely to be functionally redundant. The phenotype of atxero1ko, a higher yield of total RNA extractable from dry seeds, was complemented by introduction of the wild-type gene. Organ localization of soybean dehydrins showed that 3 genes are primarily expressed in vegetative tissues and 7 genes are primarily expressed in seeds. GmERD14 was the only soybean acidic dehydrin confirmed to be expressed at the protein level in soybean vegetative tissue. GmERD14 protein is heat stable, has cation binding activity, and can be phosphorylated similarly to the Arabidopsis vegetative acidic dehydrins. However, unlike the Arabidopsis vegetative dehydrins, GmERD14 was found not to be a cold-inducible gene. This observation suggested that the cold response pathway, especially the CBF pathway, is not functional in soybean. To determine whether the deficiency resides in the transcriptional machinery, the GmCBF transcription factors were examined. Transcript from all 7 soybean CBF genes (GmCBFs) accumulated in response to cold stress. More ever, transgenic expression of the GmCBF genes in Arabidopsis, confirmed that several GmCBF genes were functional. These results indicated that the deficiency in the soybean cold signaling pathway is downstream of the transcriptional activation of the CBF genes. Comparison of cold-sensitive germination and fatty acid content in several soybean varieties indicated that the ability to germinate after cold imbibition was a positively correlated with the amount of unsaturated fatty acids present in the seeds.

Degree

Ph.D.

Advisors

Randall, Purdue University.

Subject Area

Molecular biology|Plant biology

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