Oxidative Damage Control during Decay of Wood by Brown Rot Fungus Using Oxygen Radicals.

摘要: ABSTRACT Brown rot wood-degrading fungi deploy reactive oxygen species (ROS) to loosen plant cell walls and enable selective polysaccharide extraction. These ROS, including Fenton-generated hydroxyl radicals (HO˙), react with little specificity risk damaging hyphae secreted enzymes. Recently, it was shown that brown reduce this risk, in part, by differentially expressing genes involved HO˙ generation ahead of those coding carbohydrate-active enzymes (CAZYs). However, there are notable exceptions pattern, we hypothesized would require additional extracellular mechanisms limit ROS damage. To assess this, grew Postia placenta directionally on wood wafers spatially segregate early from later decay stages. Extracellular production (avoidance) quenching (suppression) capacities among the stages were analyzed, along ability CAZYs maintain activity postoxidation (tolerance). First, found H2O2 Fe2+ concentrations environment conducive (H2O2:Fe2+ ratio 2:1) but not (ratio 1:131) decay. Second, ABTS radical cation (antioxidant capacity) higher stages, coincident fungal phenolic concentrations. Third, surveying enzyme activities before/after exposure HO˙, early, amid more tolerant oxidative stress than expressed homologs model CAZY producer Trichoderma reesei. Collectively, indicates P. uses avoidance, suppression, tolerance mechanisms, extracellularly, complement intracellular differential expression, enabling fungus use degrade wood. IMPORTANCE Wood is one largest pools carbon Earth, its decomposition dominated most systems fungi. Wood-degrading specialize extracting sugars bound within lignin, either removing lignin first (white rot) or using “loosen” walls, sugar extraction (brown rot). Although white lignin-degrading pathways well characterized, many uncertainties mechanisms. Our study addressed a key uncertainty how without themselves they secrete. In addition revealing promote only decay, our revealed three spatial control avoid/tolerate ROS: (i) constraining Fenton reactant (H2O2, Fe2+), (ii) via antioxidants, (iii) secreting ROS-tolerant results offer insight into natural also generate targets for biotechnological development.