Strigolactones as mediators between fungi and plants

Abstract

A constantly changing environment is challenging for all organisms on Earth, especially for terrestrial plants, which face several environmental stresses despite their static way of life. In attempts to understand the mechanisms responsible for plant growth and development, scientists have recently focused on a small group of carotenoid derivatives called “strigolactones” (SLs), which are synthesized mostly in the roots in response to a variety of external factors. Strigolactones are compounds that define plant plasticity towards many environmental factors, including the establishment of mycorrhizal symbiosis under nutrient-deficient conditions. As exogenous signals, they can stimulate the branching of arbuscular mycorrhizal fungal (AMF) hyphae and as endogenous signals they adjust a plant architecture, including changes within the roots, allowing host plant and fungi to meet. SLs can also function as signaling molecules that allow colonization and establishment of the later stages of mutualistic symbioses between organisms such as AMF. SLs act on AMF metabolism by stimulating its mitochondrial respiration. Genes encoding enzymes crucial for SL biosynthesis – CCD7 and CCD8 – are also found in gymnosperm genomes, which encourages speculation that strigolactones may also be part of a host-plant and ectomycorrhizal fungi signaling pathway during the establishment of symbiosis. Nevertheless, SLs impact on ectomycorrhiza formation remain unknown. The broad spectrum of SL bioactivity has made these compounds valuable from an industrial perspective. In the future, SLs may be commercialized in plant protection products, biostimulants, or as substances used in genetic engineering to allow the creation of crops capable of growing under disadvantageous conditions.