Abstract
Isoflavonoids are a group of plant natural compounds synthesized almost exclusively by legumes, and are abundant in soybean seeds and roots. They play important roles in plant-microbial interactions and the induction of nod gene expression in Rhizobia that form nitrogen-fixing nodules on soybean roots. Isoflavonoids also contribute to the positive health effects associated with soybean consumption by humans and animals. An R1 MYB transcription factor GmMYB176 regulates isoflavonoid biosynthesis by activating chalcone synthase (CHS) 8 gene expression in soybean. Using a combination of transcriptomic and metabolomic analyses of GmMYB176-RNAi silenced (GmMYB176-Si), GmMYB176-overexpressed (GmMYB176-OE), and control soybean hairy roots, we identified a total of 33 differentially expressed genes (DEGs) and 995 differentially produced metabolite features (DPMF) in GmMYB176-Si hairy roots, and 5727 DEGs and 149 DPMFs in GmMYB176-OE hairy roots. By a targeted approach, 25 isoflavonoid biosynthetic genes and 6 metabolites were identified as differentially regulated in GmMYB176-OE and GmMYB176-Si soybean hairy roots. Taken together, our results demonstrate the complexity of isoflavonoid biosynthesis in soybean roots and suggest that a coordinated expression of pathway genes, substrate flux and product threshold level may contribute to the dynamic of the pathway regulation.
Highlights
Isoflavonoids are specialized metabolites of dual importance for plant-environment interactions
We showed that GmCHS7 and GmCHS8 genes play a critical role in isoflavonoid biosynthesis in soybean (Glycine max) seeds (Dhaubhadel et al, 2007)
Even though variations in the level of GmMYB176 transcript was observed within the sample sets, its accumulation was increased in GmMYB176-OE, and reduced in GmMYB176-Si samples compared to the controls (Supplementary Figure S1)
Summary
Isoflavonoids are specialized metabolites of dual importance for plant-environment interactions. They act as signaling molecules for symbiosis during nitrogen fixation with Rhizobia (Phillips and Kapulnik, 1995; Ferguson and Mathesius, 2003; Subramanian et al, 2006) and as phytoalexins with antimicrobial properties (Lozovaya et al, 2004a; Lygin et al, 2013). Isoflavonoids are synthesized through a legume-specific branch of phenylpropanoid pathway that is regulated by a coordinated expression of several structural genes. Studying expression levels of members of a gene family can be challenging due to their high sequence identity (Blanc and Wolfe, 2004; Shoemaker et al, 2006; Panchy et al, 2016)
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