Proteomic changes in Arthrobotrys oligospora conidia in response to benzaldehyde-induced fungistatic stress.

Soil fungistasis limits the effect of fungal agents designed to control plant-parasitic nematodes. Benzaldehyde is a fungistatic factor produced by soil microorganisms that can suppress conidial germination, but the molecular mechanism of this suppression is unknown. In this study, three conidial proteomes of Arthrobotrys oligospora ATCC24927, a nematode-trapping fungus, were obtained, quantified, and compared. Under benzaldehyde fungistatic stress, conidial protein expression profile changed significantly. Screening with a twofold selection criterion revealed 164 up-regulated and 110 down-regulated proteins. 17 proteins related to protein translation were down-regulated and gene transcription analysis suggested that the repression of proteins translation might be one mechanism by which benzaldehyde inhibites conidial germination. Benzaldehyde also resulted in the down-regulation of respiratory chain proteins and mitochondrial processes, as well as the repression of conidial DNA synthesis. In addition, the conidia up-regulated several proteins that enable it to resist benzaldehyde-induced fungistatis, and this was confirmed by a functional assessment of two knockout mutants. This study reveals putative mechanisms by which benzaldehyde causes fungistasis as well as the proteomic response of conidia to benzaldehyde. SIGNIFICANCE: Soil fungistasis limits the effect of fungal agents designed to control plant-parasitic nematodes. Benzaldehyde is one of fungistatic factors produced by soil microorganisms that can suppress conidial germination. In this study, we found that conidial protein expression profile changed significantly under benzaldehyde fungistatic stress. This research revealed new mechanistic data that describe how benzaldehyde is responsible for fungiststis by inhibiting conidial germination. Moreover, we also found that conidia can resist benzaldehyde by up-regulating proteins such as benzaldehyde dehydrogenase and heat shock proteins. This study also showed that proteomics methods play important roles in addressing soil fungistatic mechanisms.

Quantitative proteomics revealed partial fungistatic mechanism of ammonia against conidial germination of nematode-trapping fungus Arthrobotrys oligospora ATCC24927.

Ammonia is one of the fungistatic factors in soil that can suppress conidial germination, but the molecular mechanism underlying the suppression is unknown. In this study, the proteomes of fungistatic conidia, fresh conidia and germinated conidia of Arthrobotrys oligospora ATCC24927 were determined and quantified. The protein expression profile of fungistatic conidia was significantly different from those in the other two conditions. 281 proteins were down expressed in fungistatic conidia and characterized by GO annotation. Gene transcription analysis and inhibition of puromycin (a protein translation inhibitor) on conidial germination suggested that down expression of 33 protein translation related proteins might well result in repression of protein synthesis and inhibition of conidial germination. In addition, 16 down-expressed proteins were mapped to the Ras/mitogen-activated protein (Ras/MAP) regulatory networks which regulate conidial DNA synthesis. The conidial DNA synthesis was found to be definitely inhibited under by ammonia, and function studies of two Ras/MAP proteins by using knock-out strains provided partial evidence that Ras/MAP pathway regulate the conidial germination. These results suggested that down-expression of Ras/MAP related proteins might result in inhibition of DNA synthesis and finally result in inhibition conidial germination. This study revealed partial fungistatic mechanism of ammonia against conidial germination.