Strigolactones (SLs) are rhizosphere signaling molecules and phytohormones. The biosynthetic pathway of SLs in tomato has been partially elucidated, but the structural diversity in tomato SLs predicts that additional biosynthetic steps are required. Here, root RNAseq data and co-expression analysis were used for SL biosynthetic gene discovery.
This strategy resulted in a candidate gene list containing several cytochrome P450s. Heterologous expression in Nicotiana benthamiana and yeast showed that one of these, CYP712G1, can catalyze the double oxidation of orobanchol, resulting in the formation of three didehydro-orobanchol (DDH) isomers.
Virus Induced Gene Silencing (VIGS) and heterologous expression in yeast showed that one of these DDH isomers is converted to solanacol, one of the most abundant SLs in tomato root exudate. Protein modeling and substrate docking analysis suggest that hydroxy-orbanchol is the likely intermediate in the conversion from orobanchol to the DDH isomers.
Phylogenetic analysis demonstrated the occurrence of CYP712G1 homologs in the Eudicots only, which fits with the reports on DDH isomers in that clade. Protein modelling and orobanchol docking of the putative tobacco CYP712G1 homolog suggest that it can convert orobanchol to similar DDH isomers as tomato.