Functional conservation of the strigolactone biosynthetic pathway in root parasitic plants

Root parasitic plants in the Orobanchaceae family cause widespread and serious damage to crop production, especially in sub-Saharan Africa. The obligate root parasitic plants in this family, such as Striga and Orobanche, germinate in response to host root-derived small molecules called strigolactones (SLs). Facultative root parasitic plants in the same family, such as Phtheirospermum japonicum, do not require SLs for germination. However, they also sense host root-derived SLs for the chemotropic response to grow toward the host. Thus, both the obligate and facultative root parasitic plants can detect the presence of the host by sensing host-derived SLs. SLs are known to act as plant hormones that regulate shoot branching. Therefore it might be possible that root parasitic plants also can produce SLs by themselves. However, whether root parasitic plants can biosynthesize SLs has not been resolved. To address this fundamental question, we searched for SL biosynthetic genes in both obligate (Orobanche minor) and facultative (Phtheirospermum japonicum) parasitic plants and analysed the biochemical function of those gene products. Our results demonstrate that the biochemical functions of SL biosynthetic enzymes (D27, CCD7, CDD8, CYP711A, and CLAMT) in both plant species were conserved compared with the corresponding orthologs in non-parasitic plant species. Therefore, our results strongly suggest that the root parasitic plants can themselves produce SLs.