Virginia H. Goekjian

University of Georgia, Атина, Georgia, United States

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Publications (7)30.27 Total impact

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    ABSTRACT: Two separate nuclear binding activities (B1 and B2) in the soybean apical hypocotyl have been identified that interact with a palindromic C-box sequence (TGACGTCA) and which are developmentally regulated in an inverse manner. The bZIP factors responsible for these two binding activities, B1 and B2, were isolated from a cDNA library and designated STGA1 and STFs (STF1 and STF2), respectively. Sequence analysis shows that the STFs contain both a zinc-finger domain and a bZIP domain. The two zinc finger sequences of Cys4–Cys4 are most related to the RING zinc-finger motif carrying a Cys3-His-Cys4. In addition the bZIP domain of STFs is highly homologous to the HY5 protein of Arabidopsis. DNA binding studies revealed that STF1 binding to the TGACGT sequence requires distinct flanking sequences. Furthermore, STF1 binds to the Hex sequence as a heterodimer with G-box binding factors (GBFs), a feature not observed with STGA1. Since STF1 expression is most prevalent in apical and elongating hypocotyls, it is proposed that STF1 may be a transcription factor involved in the process of hypocotyl elongation.
    The Plant Journal 01/2002; 15(2):199 - 209. · 6.58 Impact Factor
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    ABSTRACT: A new member of the GT-2 family of transcription factors, GmGT-2, was isolated from soybean while screening a cDNA library with a protein binding site (D1) in the promoter of Aux28, a member of the Aux/IAA family of auxin-responsive genes. GmGT-2 possesses various primary amino acid sequence characteristics common to all GT-2 factors thus far isolated, including sequence identity in the twin trihelix DNA-binding domains. Recombinant GmGT-2 expressed in Escherichia coli binds oligotetramers of both D1 and various GT-boxes. However, unlike other known members of the GT-2 family, GmGT-2 message levels are down-regulated by light in a phytochrome-dependent manner. Evidence is presented that the expression levels of Aux28 mRNA are also down-regulated by phytochrome. These results and other referenced data implicate the possible convergence of phytochrome and auxin signaling pathways.
    Plant Molecular Biology 01/2001; 47(3):367-378. · 3.52 Impact Factor
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    [Show abstract] [Hide abstract]
    ABSTRACT: Two separate nuclear binding activities (B1 and B2) in the soybean apical hypocotyl have been identified that interact with a palindromic C-box sequence (TGACGTCA) and which are developmentally regulated in an inverse manner. The bZIP factors responsible for these two binding activities, B1 and B2, were isolated from a cDNA library and designated STGA1 and STFs (STF1 and STF2), respectively. Sequence analysis shows that the STFs contain both a zinc-finger domain and a bZIP domain. The two zinc finger sequences of Cys4-Cys4 are most related to the RING zinc-finger motif carrying a Cys3-His-Cys4. In addition the bZIP domain of STFs is highly homologous to the HY5 protein of Arabidopsis. DNA binding studies revealed that STF1 binding to the TGACGT sequence requires distinct flanking sequences. Furthermore, STF1 binds to the Hex sequence as a heterodimer with G-box binding factors (GBFs), a feature not observed with STGA1. Since STF1 expression is most prevalent in apical and elongating hypocotyls, it is proposed that STF1 may be a transcription factor involved in the process of hypocotyl elongation.
    The Plant Journal 08/1998; 15(2):199-209. · 6.58 Impact Factor
  • R T Nagao, V H Goekjian, J C Hong, J L Key
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    ABSTRACT: The promoter region of a soybean auxin-responsive gene, GmAux28, was analyzed to identify protein-binding DNA sequences that may be involved in regulation of expression. Using DNase I footprinting and gel mobility shift assays, multiple regions of interaction, including eight major protein-binding sites, were observed in the GmAux28 gene. Two sequence motifs, TGACGACA and TCCACGTGTC, related to as-1/Hex and G-box elements, respectively, found in several plant promoters, were identified. Four distinct A/T-rich domains were identified; such A/T-rich domains appear to modulate, but not to specify, the expression of many genes. Two new sequence motifs, delta-1 (D1) and delta-4 (D4) were also identified. D1 and D4 share a very similar core sequence, TAGTxxCTGT and TAGTxCTGT, respectively. In gel mobility shift analyses, D1 and D4 elements exhibit a complex interaction of binding proteins. The GmAux22 promoter also contains D1-related elements which compete with the GmAux28 elements. Sequence comparisons have identified D1/D4-like sequences in several other auxin-responsive genes suggesting the possible importance of D1/D4 and the respective binding proteins in the regulation of expression of these genes.
    Plant Molecular Biology 04/1993; 21(6):1147-62. · 3.52 Impact Factor
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    J A Kimpel, R T Nagao, V Goekjian, J L Key
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    ABSTRACT: The transcriptional response of soybean (Glycine max) seedlings during heat shock (HS) was investigated under two different treatment regimes. During prolonged heat treatment at 40 degrees C, active transcription of the HS genes (as measured by "runoff" transcription assays) occurs only during the first few hours. Nonetheless, mRNAs for these genes are present at relatively high abundance even after 9 hours of exposure to 40 degrees C. Because HS mRNAs have a fairly short half-life (less than 3 hours) at 28 degrees C, these results indicate that HS mRNAs are inherently more stable at 40 degrees C. During a second type of heat treatment regime-short pulses of high (45 degrees C) heat followed by 1 to 2 hours at 28 degrees C-transcription of HS genes is comparable to that achieved at 40 degrees C for the first few hours, even though the tissue is maintained at non-HS temperatures. The transcriptional responses to these two different heat treatments indicate that regulatory controls for the transcription of the HS genes must involve more than a simple sensing of ambient temperature, since transcription of these genes can be turned off at 40 degrees C (in the case of prolonged exposure) and can continue at 28 degrees C (following a short, severe heat treatment). Additional results demonstrate that the response of soybean seedlings to a particular HS depends on their prior exposure to heat; seedlings given a preheat treatment (that is known to induce thermotolerance) respond more moderately to a short heat pulse at 45 degrees C. Overall, this research indicates that plants have mechanisms for both monitoring the severity of changes in temperature and for measuring the magnitude and duration of the stress. Such information is then used to regulate the plant's response to heat both transcriptionally and posttranscriptionally.
    Plant physiology 12/1990; 94(3):988-95. · 6.56 Impact Factor
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    ABSTRACT: Two genes from Arabidopsis thaliana related to the auxin-inducible Aux28 and Aux22 genes of soybean have been isolated. These genes belong to a small multi-gene family and are similar to the soybean Aux gene family in the sequence of the predicted proteins, intron/exon locations, and auxin-enhanced expression of their transcripts. Application of auxin to 8-day old Arabidopsis plants, 4-day old etiolated seedlings, and suspension culture cells all resulted in enhanced Aux transcript levels. Comparison of the promoter sequences from the soybean and Arabidopsis genes yielded no significant sequence conservation; however, three regions of near sequence identity are present between the two Arabidopsis Aux genes.
    Plant Molecular Biology 01/1990; 15(4):623-632. · 3.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The transcription response of soybean (Glycine max) seedlings during heat shock (HS) was investigated under two different treatment regimes. During prolonged heat treatment at 40°C, active transcription of the HS genes (as measured by runoff transcription assays) occurs only during the first few hours. Nonetheless, mRNAs for these genes are present at relatively high abundance even after 9 hours of exposure to 40°C. Because HS mRNAs have a fairly short half-life (less than 3 hours) at 28°C, these results indicate that HS mRNAs are inherently more stable at 40°C. During a second type of heat treatment--short pulses of high (45°C) heat followed by 1 to 2 hours at 28°C--transcription of HS genes is comparable to that achieved at 40°C for the first few hours, even though the tissue is maintained at non-HS temperatures. The transcriptional responses to these two different heat treatments indicate that regulatory controls for the transcription of the HS genes must involve more than a simple sensing of ambient temperature, since transcription of these genes can be turned off at 40°C (in the case of prolonged exposure) and can continue at 28°C (following a short, severe heat treatment). Additional results demonstrate that the response of soybean seedlings to a particular HS depends on their prior exposure to heat; seedlings given a preheat treatment (that is known to induce thermotolerance) respond more moderately to a short heat pulse at 45°C. Overall, this research indicates that plants have mechanisms for both monitoring the severity of changes in temperature and for measuring the magnitude and duration of the stress. Such information is then used to regulate the plant's response to heat both transcriptionally and posttranscriptionally.
    Plant Physiology - PLANT PHYSIOL. 01/1990; 94(3):988-995.