Wang Tao, Tian Zhaomo, Tunlid Anders, Persson Per
Department of Biology, Microbial Ecology Group, Lund University, Ecology Building, SE-223 62, Lund, Sweden.
Centre for Environmental and Climate Research (CEC), Lund University, Ecology Building, SE-223 62, Lund, Sweden.
New Phytol. 2020 Oct;228(2):697-711. doi: 10.1111/nph.16596. Epub 2020 May 12.
In nitrogen (N)-limited boreal forests, trees depend on the decomposing activity of their ectomycorrhizal (ECM) fungal symbionts to access soil N. A large fraction of this N exists as proteinaceous compounds associated with mineral particles. However, it is not known if ECM fungi can access these mineral-associated proteins; accordingly, possible acquisition mechanisms have not been investigated. With tightly controlled isotopic, spectroscopic, and chromatographic experiments, we quantified and analyzed the mechanisms of N acquisition from iron oxide mineral-associated proteins by Paxillus involutus, a widespread ECM fungus in boreal forests. The fungus acquired N from the mineral-associated proteins. The collective results indicated a proteolytic mechanism involving formation of the crucial enzyme-substrate complexes at the mineral surfaces. Hence, the enzymes hydrolyzed the mineral-associated proteins without initial desorption of the proteins. The proteolytic activity was suppressed by adsorption of proteases to the mineral particles. This process was counteracted by fungal secretion of mineral-surface-reactive compounds that decreased the protease-mineral interactions and thereby promoted the formation of enzyme-substrate complexes. The ability of ECM fungi to simultaneously generate extracellular proteases and surface-reactive metabolites suggests that they can play an important role in unlocking the large N pool of mineral-associated proteins to trees in boreal forests.
在氮（N）受限的北方森林中，树木依赖其外生菌根（ECM）真菌共生体的分解活动来获取土壤中的氮。这种氮的很大一部分以与矿物颗粒相关的蛋白质化合物形式存在。然而，尚不清楚ECM真菌是否能够获取这些与矿物相关的蛋白质；因此，尚未对可能的获取机制进行研究。通过严格控制的同位素、光谱和色谱实验，我们对北方森林中广泛存在的ECM真菌卷缘桩菇从氧化铁矿物相关蛋白质中获取氮的机制进行了量化和分析。该真菌从与矿物相关的蛋白质中获取氮。总体结果表明存在一种蛋白水解机制，该机制涉及在矿物表面形成关键的酶 - 底物复合物。因此，这些酶能够水解与矿物相关的蛋白质，而无需蛋白质先进行解吸。蛋白酶吸附到矿物颗粒上会抑制蛋白水解活性。真菌分泌的矿物表面反应性化合物可抵消这一过程，这些化合物会减少蛋白酶与矿物的相互作用，从而促进酶 - 底物复合物的形成。ECM真菌同时产生细胞外蛋白酶和表面反应性代谢物的能力表明，它们在为北方森林中的树木释放大量与矿物相关的蛋白质中的氮库方面可以发挥重要作用。
