Abstract
The lignin peroxidase (LIP) production and regulation, in manganese ions (Mn2+) deficient cultures of the white rot fungus Phanerochaete chrysosporium, is still not clearly understood. Mn2+ deficiency is correlated to low levels of manganese containing superoxide dismutase (MnSOD). In this work, we show that despite the low activity level of MnSOD in Mn2+-deficient cultures, the presence of H2O2 is essential for the expression of the lip-H2 gene, which encodes for the major LIP isoenzyme produced (LIP-H2). Thus, the H2O2 present in Mn2+-deficient cultures is probably produced by other mechanisms rather than dismutation of superoxide ions by MnSOD. Glyoxal oxidase gene (glox) expression was significantly higher than MnSOD (MnSOD1) and cellobiose dehydrogenase (cdh1) expression in Mn2+-deficient cultures, indicating its clear involvement in H2O2 production in those cultures. Glyoxal oxidase may compensate the absence of MnSOD activity in Mn2+-deficient cultures. The high levels of reactive oxygen species (ROS) needed for the enhancement of LIP expression in Mn2+-deficient cultures were not directly correlated to the protein kinase C (PKC) activity involved in signal transduction pathway. High level of oxidative stress was observed in MnSOD silenced mutants, grown in the presence of Mn2+, indicating that oxidative stress in Mn2+-deficient cultures was caused by low levels of MnSOD rather than the deficiency in Mn2+. The results of this work can further contribute to the understanding of LIP regulation in Mn2+-deficient cultures.
Highlights
Lignin is an amorphous and insoluble polymer lacking stereoregularity, which plays a key role in the carbon cycle as the most abundant aromatic compound and as a protective matrix surrounding the cellulose microfibrils of plant cell walls [1] [2]
Higher level of oxidative stress was confirmed in manganese containing superoxide dismutase (MnSOD) silenced mutant (MSC1) in comparison to MnSOD non-silenced mutant (Bar5), by measuring lower GSH/GSSG ratio and higher level of oxidized lipids, in spite of the presence of Mn2+ in the medium
Results obtained with BAR5 are comparable to that reported in the past for the highest lignin peroxidase (LIP)-producing oxygenated cultures [6]
Summary
Lignin is an amorphous and insoluble polymer lacking stereoregularity, which plays a key role in the carbon cycle as the most abundant aromatic compound and as a protective matrix surrounding the cellulose microfibrils of plant cell walls [1] [2]. The most intensively studied white rot fungus, Phanerochaete chrysosporium, secretes an array of peroxidases that act via the generation of aromatic free radicals, which undergo spontaneous cleavage reactions. Two major families of hydrogen peroxide (H2O2)-requiring extracellular heme-peroxidases designated lignin peroxidase (LIP) and manganese-dependent peroxidase (MNP) were identified [5]. The regulation of the gene families encoding extracellular peroxidases is poorly understood, but it is clear that oxidative stress is a key factor [6]-[8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
