Emerging roles of strigolactones in plant responses toward biotic stress

Strigolactones are plant hormones that regulate plant growth and development, particularly in response to nutrient deficiency. However, they are also exuded from roots into the rhizosphere to promote symbiosis with beneficial microorganisms. This multimodal action makes the research both interesting and complex, particularly in terms of how strigolactones evolved. Interest has been growing in recent years about whether strigolactones also influence pathogenic organisms and/or plant responses to disease. In general, strigolactones seem to afford a positive effect on plant biotic stress tolerance. Some of this may be by directly inhibiting microbes in the soil, and some by promoting internal plant responses, such as induction of stress hormone pathways and stomata closure. However, the research is still in its infancy. The complex and possibly multimodal actions by strigolactones seem to depend on the type of disease and the species (or even species variety) that are involved. This chapter summarizes the research up until now and expectations for the future.