Abstract
Much research has been conducted on the changes in gene expression of the model plant Arabidopsis to low-oxygen stress. Flooding results in a low oxygen environment in the root zone. However, there is ample evidence that tolerance to soil flooding is more than tolerance to low oxygen alone. In this study, we investigated the physiological response and differential expression of root-related transcription factors (TFs) associated with the tolerance of soybean plants to soil flooding. Differential responses of PI408105A and S99-2281 plants to ten days of soil flooding were evaluated at physiological, morphological and anatomical levels. Gene expression underlying the tolerance response was investigated using qRT-PCR of root-related TFs, known anaerobic genes, and housekeeping genes. Biomass of flood-sensitive S99-2281 roots remained unchanged during the entire 10 days of flooding. Flood-tolerant PI408105A plants exhibited recovery of root growth after 3 days of flooding. Flooding induced the development of aerenchyma and adventitious roots more rapidly in the flood-tolerant than the flood-sensitive genotype. Roots of tolerant plants also contained more ATP than roots of sensitive plants at the 7th and 10th days of flooding. Quantitative transcript analysis identified 132 genes differentially expressed between the two genotypes at one or more time points of flooding. Expression of genes related to the ethylene biosynthesis pathway and formation of adventitious roots was induced earlier and to higher levels in roots of the flood-tolerant genotype. Three potential flood-tolerance TFs which were differentially expressed between the two genotypes during the entire 10-day flooding duration were identified. This study confirmed the expression of anaerobic genes in response to soil flooding. Additionally, the differential expression of TFs associated with soil flooding tolerance was not qualitative but quantitative and temporal. Functional analyses of these genes will be necessary to reveal their potential to enhance flooding tolerance of soybean cultivars.
Highlights
Flooding is a common environmental stress that impacts plant growth and reduces soybean grain yield in the humid temperate region of the United States, where heavy rainfall can exceed surface and subsurface drainage capabilities [1,2,3]
To gain an understanding of gene expression associated with the tolerance response of PI408105A to soil flooding, high-throughput Quantitative Reverse-Transcription PCR (qRT-PCR) was conducted with 169 root-related transcription factor genes
Controlled experiments on young soybean plants conducted under greenhouse conditions confirmed results from field studies that indicated greater flooding tolerance of PI408105A than S99-2281
Summary
Flooding is a common environmental stress that impacts plant growth and reduces soybean grain yield in the humid temperate region of the United States, where heavy rainfall can exceed surface and subsurface drainage capabilities [1,2,3]. Of all the Arabidopsis genes examined are differentially expressed in response to low-oxygen stress [10,12,13,14,35,36,37]. Liu et al [12] reported that 2085 genes in the whole-genome amplicon arrays of 26,777 genes showed significant differential expression to low-oxygen These genes were involved in a wide range of biological processes, molecular functions, cellular components and metabolic pathways as identified by gene ontology analysis. Banti et al [52] reported that over expression of the heat shock transcription factor HsfA2 enhances the tolerance of transgenic Arabidopsis plants to heat and to anoxia and submergence stress. Identification of additional TFs and understanding their molecular mechanism and function could enhance development of cultivars that have the ability to overcome flooding stress for the benefit of soybean producers, especially in regions where soil drainage is either impractical or impossible
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