Abstract
Although there are many antimicrobial proteins in plants, they are not well-explored. Understanding the mechanism of action of plant antifungal proteins (AFPs) may help combat fungal infections that impact crop yields. In this study, we aimed to address this gap by screening Oryza sativa leaves to isolate novel AFPs. We identified a thioredoxin protein with antioxidant properties. Being ubiquitous, thioredoxins (Trxs) function in the redox balance of all living organisms. Sequencing by Edman degradation method revealed the AFP to be O. sativa Thioredoxin m-type isoform (OsTrxm). We purified the recombinant OsTrxm and its cysteine mutant proteins (OsTrxm C/S) in Escherichia coli. The recombinant OsTrxm proteins inhibited the growth of various pathogenic fungal cells. Interestingly, OsTrxm C/S mutant showed higher antifungal activity than OsTrxm. A growth inhibitory assay against various fungal pathogens and yeasts confirmed the pertinent role of cysteine residues. The OsTrxm protein variants penetrated the fungal cell wall and membrane, accumulated in the cells and generated reactive oxygen species. Although the role of OsTrxm in chloroplast development is known, its biochemical and molecular functions have not been elucidated. These findings suggest that in addition to redox regulation, OsTrxm also functions as an antimicrobial agent.
Highlights
As sessile organisms, plants are continuously exposed to diverse biotic/abiotic factors, such as pathogens, adverse climates, and hormones
To isolate a novel antifungal proteins (AFPs) from natural sources, crude proteins were extracted from the rice leaves which were homogenized with liquid nitrogen
SEC was applied to purify pure AFP in Superdex 200 column (Figure 1B) and the antifungal effect of the presented fractions was ascertained against F. moniliforme conidia
Summary
Plants are continuously exposed to diverse biotic/abiotic factors, such as pathogens, adverse climates, and hormones. In their defense against external pathogenic attacks, antimicrobial proteins play an important role. Antioxidants 2019, 8, 598 proteins (AFPs) are not well understood. This is significant since decreases in crop yield ire often attributed to fungal infections. Thioredoxin proteins act as antioxidants in various ubiquitous cellular processes, including the activation of ribonucleotide reductase, regulation of transcription factors, ROS scavenging, and the photosynthetic pathway in plant cells [1,2,3,4,5,6]. According to subcellular localization and sequence similarity of Trx proteins, 15 subgroups have been classified [8,9,10,11]
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