Strigolactones, a new hormone group with roles in plant-microbe interactions

Plants use a range of signals to regulate their growth, development and response to the environment, foremost the small, potent plant hormones. The discovery of strigolactones (SLs) in 2008 as only the ninth plant hormone group has given rise to a new field of research examining the roles of SLs in plants. SLs are ancient signals present in algae to flowering plants and can act as both internal hormones and rhizosphere signals. SLs have roles throughout the plant, from shoot and root architecture to interactions with symbiotic microbes. Given the widespread nature of SLs across plant species and the current interest in manipulating crop SLs to manage plant architecture, symbiotic relationships and parasitic weed interactions it is essential that we gain an understanding of the role of SLs in plant-pathogen interactions. This work investigates these interactions using two model pathosystems between garden pea (Pisum sativum L.) and the soil-borne pathogens, Pythium irregularum and Fusarium oxysporum f.sp. pisi. We found no evidence that synthetic SLs could directly influence the growth of either pathogen in culture, indicating that unlike interactions with symbiotic arbuscular mycorrhizal fungi, SLs are not likely to act as rhizosphere signals in these plant-pathogen interactions. SL-deficient pea mutants challenged with Pythium irregulare and Fusarium oxysporum f.sp. pisi developed disease symptoms in a similar manner to wild type plants, indicating SLs are unlikely to play a significant role in response to these particular diseases in pea. In contrast, parallel studies with ethylene-insensitive pea mutants suggest a positive role for ethylene in response to P. irregulare.