Symbiotic Cooperation in the Biosynthesis of a Phytotoxin

摘要

Natural products play a key role in symbiotic interactions between microorganisms and higher organisms, covering all kingdoms of life.The function of these secondary metabolites may range from signaling compounds in mutualism to virulence factors and antibiotics in parasitic relationships. In many cases the interactions involve multiple partners and thus the biogenetic basis of chemical mediators can be quite complex. This complexity is well exemplified by the unparalleled tripartite relationship among the rice-seedling-blight fungus Rhizopus microsporias, its host plant Oryza sativa and endosymbiotic bacteria that reside in the fungal cytosol. The bacterial symbionts (Burkholderia species) produce a phytotoxin complex to assist the phytopathogenic fungus in colonizing rice seedlings. In turn the bacteria profit from a safe niche and access to nutrients released from the decaying plant. Initially, the macrolide rhizoxin (1, Figure 1) and various congeners such as WF-1360F (2) were isolated from cultures of R. microsporias van Tieghem var. chinensis and identified as the causative agent of rice seedling blight.