Browsing by Author "Yamasaki, Yuji"

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    The Ethylene Signaling Pathway Negatively Impacts CBF/DREB-Regulated Cold Response in Soybean (Glycine max)
    (Frontiers, 2019) Robison, Jennifer D.; Yamasaki, Yuji; Randall, Stephen K.; Biology, School of Science
    During cold stress, soybean CBF/DREB1 transcript levels increase rapidly; however, expected downstream targets appear unresponsive. Here we asked whether the ethylene signaling pathway, which is enhanced in the cold can negatively regulate the soybean CBF/DREB1 cold responsive pathway; thus contributing to the relatively poor cold tolerance of soybean. Inhibition of the ethylene signaling pathway resulted in a significant increase in GmDREB1A;1 and GmDREB1A;2 transcripts, while stimulation led to decreased GmDREB1A;1 and GmDREB1B;1 transcripts. A cold responsive reporter construct (AtRD29Aprom::GFP/GUS), as well as predicted downstream targets of soybean CBF/DREB1 [ Glyma.12g015100 (ADH), Glyma.14g212200 (ubiquitin ligase), Glyma.05g186700 (AP2), and Glyma.19g014600 (CYP)] were impacted by the modulation of the ethylene signaling pathway. Photosynthetic parameters were affected by ethylene pathway stimulation, but only at control temperatures. Freezing tolerance (as measured by electrolyte leakage), free proline, and MDA; in both acclimated and non-acclimated plants were increased by silver nitrate but not by other ethylene pathway inhibitors. This work provides evidence that the ethylene signaling pathway, possibly through the action of EIN3, transcriptionally inhibits the CBF/DREB1 pathway in soybean.
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    Functionality of soybean CBF/DREB1 transcription factors
    (Elsevier, 2016-05) Yamasaki, Yuji; Randall, Stephen K.; Department of Biology, School of Science
    Soybean (Glycine max) is considered to be cold intolerant and is not able to significantly acclimate to cold/freezing stress. In most cold tolerant plants, the C-repeat/DRE Binding Factors (CBF/DREBs) are critical contributors to successful cold-responses; rapidly increasing following cold treatment and regulating the induction of many cold responsive genes. In soybean vegetative tissue, we found strong, transient accumulation of CBF transcripts in response to cold stress; however, the soybean transcripts of typical cold responsive genes (homologues to Arabidopsis genes such as dehydrins, ADH1, RAP2.1, and LEA14) were not significantly altered. Soybean CBFs were found to be functional, as when expressed constitutively in Arabidopsis they increased the levels of AtCOR47 and AtRD29a transcripts and increased freezing tolerance as measured by a decrease in leaf freezing damage and ion leakage. Furthermore the constitutive expression of GmDREB1A;2 and GmDREB1B;1 in Arabidopsis led to stronger up-regulation of downstream genes and more freezing tolerance than GmDREB1A;1, the gene whose transcript is the major contributor to total CBF/DREB1 transcripts in soybean. The inability for the soybean CBFs to significantly up regulate the soybean genes that contribute to cold tolerance is consistent with poor acclimation capability and the cold intolerance of soybean.
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    Glycine max and Glycine soja are capable of cold acclimation
    (Wiley, 2017-12) Robison, Jennifer; Arora, Nigam; Yamasaki, Yuji; Saito, M.; Boone, J.; Blacklock, Brenda; Randall, Stephen; Biology, School of Science
    Soybean has been considered a cold intolerant species; based largely upon seed germination and soil emergent evaluations. This study reports a distinct acquisition of cold tolerance, in seedlings, following short acclimation periods. Diversity in cold responses was assessed in eight cultivars of Glycine max and six accessions of G. soja. All varieties of soybean significantly increased in freezing tolerance following acclimation. This study indicates soybean seedlings are indeed capable of sensing cold and acquiring cold tolerance. Germination rates after cold imbibition were negatively correlated with maturity group, but positively correlated with cold acclimation potential in G. soja. Seed fatty acid composition was varied between the species, with Glycine soja accessions containing about 2-times more linolenic acid (18:3) than G. max. Furthermore, high levels of linoleic acid (18:2) in seeds were positively correlated with germination rates following cold imbibition in G. soja only. We suggest that domestication has not impacted the overall ability of soybean to cold acclimate at the seedling stage and that there is little variation within the domesticated species for ability to cold acclimate. Thus, this brief comparative study reduces the enthusiasm for the “wild” species as an additional source of genetic diversity for cold tolerance.