Functional expression of two NADPH-cytochrome P450 reductases from Siraitia grosvenorii

Cytochrome P450 reductase (CPR) is the redox partner of various P450s involved in primary and secondary metabolism. Here, we identified and characterized two paralogs of cytochrome P450 reductase from Siraitia grosvenorii. There were two full-length CPR isoforms in the S. grosvenorii fruit transcriptome dataset. They had the same open reading frames of 2, 124 bp, encoding 707 amino acids. A phylogenetic analysis characterized both SgCPR1 and SgCPR2 as Class II dicotyledonous CPRs. The recombinant proteins SgCPR1 and SgCPR2 could reduce cytochrome c and ferricyanide in a NADPH-dependent manner. The SgCPR1 and SgCPR2 transcripts were detected in all examined tissues of S. grosvenorii, and in fresh fruit, they had expression patterns similar to several key enzymes that require CPR as a partner during their biosynthesis. The expression levels of the SgCPRs were induced after a methyl jasmonate treatment. The extracts from yeast co-expressing SgCPR1/SgCPR2 and the cytochrome P450 enzyme CYP76AH1 produced ferruginol, indicating the positive effects of SgCPR1/SgCPR2 on the CYP76AH1 activity. A docking analysis confirmed the experimentally deduced functional activities of SgCPR1 and SgCPR2 for NADPH, FAD and FMN. Thus, SgCRP1 and SgCPR2 are both likely to participate in secondary metabolism, especially mogroside biosynthesis in S. grosvenorii.