The role of strigolactones in plant disease

Strigolactones (Sls) have important roles in interactions with beneficial microbes, including as a rhizoshphere signal in arbuscular mycorrhizal (AM) fungal associations and in the roots of legumes during nodulation. However, the potential role of SLs in interactions with pathogenic microbes has only recently begun to be explored, with limited evidence for a positive role in disease protection against foliar fungal pathogens in tomato. Given the production of Sls by roots, with roles both inside and outside the plant we explored the role of Sls in development of root diseases using garden pea (Pisum sativum L.) as a model system. We examined interactions with a soil-borne pathogen, the oomycete Pythium irregulare that causes necrotrophic root rot. In vitro studies provided no evidence that synthetic SL could directly influence the growth of this pathogen in culture, indicating that Sls are not likely to act as rhizosphere signals in this plant-pathogen interactions. When grown with Pythium irregularum, pea mutants defective in key steps of SL biosynthesis, Psccd7 and Psccd8, and SL-insensitive mutant Psf-box, developed disease symptoms in a similar manner to wild type plants, indicating Sls are unlikely to play a significant role in response to this disease in pea. Consistent with this, we found SL production was not significantly altered in Pythium irregulare infected wild type plants. In contrast, parallel studies with an ethyleneinsensitive pea mutant, Psein2, suggest a positive role for ethylene in response to P. irregulare. This work is currently being expanded to look at other root pathogens including the true fungi Fusarium oxysporum f. sp. pisi that grows as a hemibiotroph and leads to vascular wilt of pea.