Twin anchors of the soybean isoflavonoid metabolon: evidence for tethering of the complex to the endoplasmic reticulum by IFS and C4H.

Dastmalchi, M., Bernards, M.A., and Dhaubhadel, S. (2016). "Twin anchors of the soybean isoflavonoid metabolon: evidence for tethering of the complex to the endoplasmic reticulum by IFS and C4H.", The Plant Journal, 85(6), pp. 689-706. doi : 10.1111/tpj.13137  Access to full text

Abstract

Isoflavonoids are specialized plant metabolites, almost exclusive to legumes, and their biosynthesis forms a branch of the diverse phenylpropanoid pathway. Plant metabolism can be coordinated at many strata, including the formation of protein complexes, or ‘metabolons’, which represent the molecular level of organization. Here, we have substantiated the long-postulated isoflavonoid metabolon by identifying elements of the complex, their subcellular localizations and interactions. Isoflavone synthase (IFS) and cinnamate 4-hydroxylase (C4H) have been determined to be tandem P450 enzymes, anchored in the ER, interacting with soluble enzymes of the phenylpropanoid and isoflavonoid pathways (C4H, CHS, CHR and CHI). The soluble enzymes of these pathways, whether localized to the cytoplasm or nucleus, are tethered to the ER through interaction with these P450s. The complex is also held together by interactions between the soluble elements. We have shown evidence for IFS interaction with upstream, and non-consecutive enzymes. Such a protein complex describes a possible mechanism for the flux of metabolites into the isoflavonoid pathway. Further, through interaction studies we identified several candidates that are associated with GmIFS2, an isoform of IFS, in soybean hairy roots. This list could provide additional candidates for various biosynthetic and structural elements that are involved in isoflavonoid production. Our interaction studies provide valuable information about isoform specificity, among isoflavonoid enzymes, which can guide future engineering of the pathway in legumes or help overcome bottlenecks in heterologous expression.

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