Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Dr. Sangeeta Dhaubhadel

2nd Supervisor

Dr. Mark Bernards

Joint Supervisor


MYB transcription factors are one of the largest transcription factor families characterized in plants. They are classified into four types: R1 MYB, R2R3 MYB, R3 MYB and R4 MYB. GmMYB176 is an R1MYB transcription factor that regulates Chalcone synthase (CHS8) gene expression and isoflavonoid biosynthesis in soybean. Silencing of GmMYB176 suppressed the expression of the GmCHS8 gene and reduced the accumulation of isoflavonoids in soybean hairy roots. However, overexpression of GmMYB176 does not alter either GmCHS8 gene expression or isoflavonoid levels suggesting that GmMYB176 alone is not sufficient for GmCHS8 gene regulation. I hypothesized that GmMYB176 acts cooperatively with another factor(s) for the regulation of GmCHS8 gene expression and it may also regulate other isoflavonoid biosynthetic genes in soybean. The objective of this research was to identify the GmMYB176 interactome for GmCHS8 gene regulation and elucidate the role of GmMYB176 in isoflavonoid biosynthesis in soybean. GmMYB176 interacting proteins were identified using two translational fusion baits (GmMYB176-YFP and YFP-GmMYB176) by co-immunoprecipitation, followed by liquid chromatography-tandem mass spectrometry. The interaction of selected candidates with GmMYB176 was validated in planta and their DNA binding activities determined. GmMYB176 may form a transcriptional complex with Gm04bZIP and/or Gm05bZIP for the regulation of GmCHS8 gene expression. RNA-seq and metabolomics analyses of soybean hairy roots in which GmMYB176 was either silenced or over-expressed revealed that GmMYB176 regulates multiple genes in the isoflavonoid biosynthesis pathway, affecting the production of metabolites in phenylpropanoid pathway such as phenylalanine, liquiritigenin, daidzin, genistin, glycitein, and glyceollin. The knowledge and information generated on the role of GmMYB176 in the regulation of isoflavonoid biosynthesis will allow genetic manipulation of isoflavonoid level in soybean and/or introduce isoflavonoid pathway in non-legumes.