Isoflavonoid-specific prenyltransferase gene family in soybean: GmPT01, a pterocarpan 2-dimethylallyltransferase involved in glyceollin biosynthesis.

Phytoalexin glyceollins are soybean-specific antimicrobial compounds that are derived from the isoflavonoid pathway. They are synthesized by soybean in response to extrinsic stress such as pathogen attack or injury, thereby conferring partial resistance if synthesized rapidly at the site of infection and at the required concentration. Soybean produces multiple forms of glyceollins that result from the differential prenylation reaction catalyzed by prenyltransferases (PTs) on either the C-2 or C-4 carbon of a pterocarpan glycinol. The soybean genome contains 77 PT-encoding genes (GmPTs) where at least 11 are (iso)flavonoid-specific. Transcript accumulation of five candidates GmPTs was increased in response to Phytophthora sojae infection, suggesting their role in phytoalexin synthesis. The induced GmPTs localize to plastids and display tissue-specific expression. We have in this study identified two additional GmPTs: an isoflavone dimethylallyltransferase 3 (IDT3); and a glycinol 2-dimethylallyl transferase GmPT01. GmPT01 prenylates (-)-glycinol at the C-2 position, localizes in the plastid, and exhibits root-specific gene expression. Furthermore, its expression is induced rapidly in response to stress, and is associated with a quantitative trait loci linked with resistance to P. sojae. Based on these results, we conclude that GmPT01 are possibly one of the loci involved in conferring partial resistance against stem and root rot disease in soybean.