Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108, USA.
Fungal Genet Biol. 2012 Jul;49(7):578-87. doi: 10.1016/j.fgb.2012.05.001. Epub 2012 May 12.
Highly diverse communities of microbial symbionts occupy eukaryotic organisms, including plants. While many well-studied symbionts may be characterized as either parasites or as mutualists, the prevalent but cryptic endophytic fungi are less easily qualified because they do not cause observable symptoms of their presence within their host. Here, we investigate the interactions of an endophytic fungus, Fusarium verticillioides with a pathogen, Ustilago maydis, as they occur within maize (Zea mays). We used experimental inoculations to evaluate metabolic mechanisms by which these three organisms might interact. We assessed the impacts of fungal-fungal interactions on endophyte and pathogen growth within the plant, and on plant growth. We find that F. verticillioides modulates the growth of U. maydis and thus decreases the pathogen's aggressiveness toward the plant. With co-inoculation of the endophyte with the pathogen, plant growth is similar to that which would be gained without the pathogen present. However, the endophyte may also break down plant compounds that limit U. maydis growth, and obtains a growth benefit from the presence of the pathogen. Thus, an endophyte such as F. verticillioides may function as both a defensive mutualist and a parasite, and express nutritional modes that depend on ecological context.
高度多样化的微生物共生体群落栖息在真核生物中，包括植物。虽然许多研究充分的共生体可以被定性为寄生虫或互利共生体，但普遍存在但隐蔽的内生真菌则不太容易被定性，因为它们在宿主体内不会引起明显的存在症状。在这里，我们研究了内生真菌镰刀菌（Fusarium verticillioides）与病原体玉米黑粉菌（Ustilago maydis）在玉米（Zea mays）中的相互作用。我们使用实验接种来评估这三个生物体可能相互作用的代谢机制。我们评估了真菌-真菌相互作用对植物内生菌和病原体生长以及植物生长的影响。我们发现，镰刀菌会调节玉米黑粉菌的生长，从而降低病原体对植物的侵袭性。内生菌与病原体共同接种时，植物的生长与没有病原体存在时相似。然而，内生菌也可能分解限制玉米黑粉菌生长的植物化合物，并从病原体的存在中获得生长优势。因此，像镰刀菌这样的内生菌可能同时充当防御性互利共生体和寄生虫，并表现出依赖于生态背景的营养模式。
