MONOLIGNOL GLUCOSIDES AS SPECIFIC RECOGNITION MESSENGERS IN FUNGUS-PLANT SYMBIOSES

Most land plants harbour endophytic fungi within their tissues. Such endophytes, which often do not damage their host, provide useful models to study mutualistic and pathogenic fungus-plant symbioses. In the Xylariaceae a family of mostly endophytic fungi, ascospores are irreversibly activated, prior to germination, within minutes of contact with a potential host. This activation was studied to establish the biochemical nature and specificity of recognition between these fungi and various host plants. Ascospores of different xylariaceous species can recognize different plant species. The biochemical signature responsible for this recognition is provided by mixtures of monolignols, including the glycosides Z-isoconiferin and Z-syringin, released to the plant surface from small wounds in the bark. Dose-response curves for ascospore activation by crude extracts and by the purified monolignols demonstrate that these compounds can act as high-affinity messengers, and that spores can distinguish structurally similar monolignols, leading us to postulate the existence of specific receptors for these molecules in fungal spores. © 1991.