Abstract
We investigated the properties of platelet-activating factor acetylhydrolase (PAF-AH) derived from Trichoderma harzianum. The enzyme, comprised of 572 amino acids, shares high homology with PAF-AH proteins from T. koningii and other microbial species. The optimum enzymatic activity of PAF-AH occurred at pH 6 in the absence of Ca2+ and it localized in the cytoplasm, and we observed the upregulation of PAF-AH expression in response to carbon starvation and strong heat shock. Furthermore, PAF-AH knockout transformant growth occurred more slowly than wild type cells and over-expression strains grown in SM medium at 37°C and 42°C. In addition, PAF-AH expression significantly increased under a series of maize root induction assay. Eicosanoic acid and ergosterol levels decreased in the PAF-AH knockouts compared to wild type cells, as revealed by GC/MS analysis. We also determined stress responses mediated by PAF-AH were related to proteins HEX1, Cu/Zn superoxide dismutase, and cytochrome c. Finally, PAF-AH exhibited antagonistic activity against Rhizoctonia solani in plate confrontation assays. Our results indicate PAF-AH may play an important role in T. harzianum stress response and antagonism under diverse environmental conditions.
Highlights
The platelet-activating factor acetylhydrolase (PAF-AH) belongs to the phospholipase A2 (PLA2) enzyme superfamily
We currently observed Trichoderma harzianum (T28) PAF-AH expression was significantly upregulated under heat stimulus and that T28 PAF-AH transformants grew more slowly than the wild type strain. These results indicate PAF-AH plays an important role in Trichoderma stress response, but little information is available regarding its physiological function(s)
The PAF-AH of T. harzianum T28 was located with other ascomycete sequences, and it formed a distinct subclade with a PAF-AH protein from T. koningii, supported by a bootstrap value of 100%
Summary
The platelet-activating factor acetylhydrolase (PAF-AH) belongs to the phospholipase A2 (PLA2) enzyme superfamily. These enzymes hydrolyze ester bonds at the sn-2 position of glycerophospholipids to release free fatty acids and lysophospholipids, which often trigger signal transduction pathways in animal or human cells. PAF-AH is involved in human health and disease by promoting proinflammation [4,5] and mediating stress responses in eukaryotic cells. Et al [6] reported intracellular type II PAF-AH could protect against oxidative stress-induced hepatic injury by metabolizing oxidized phospholipids. The PAF-AH gene in Saccharomyces cerevisiae significantly enhances the yeast’s resistance to oxidative stress [7]
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