|Waewthongrak, Waewruedee - Prince Of Songkla University|
|Leelasuphakul, Wichitra - Prince Of Songkla University|
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2014
Publication Date: 10/15/2014
Citation: Waewthongrak, W., Mccollum, T.G., Leelasuphakul, W. 2014. Cyclic lipopeptides from Bacillus subtilis ABS-S14 elicit defense-related gene expression in citrus fruit. PLoS One. 9(10):1-11.
Interpretive Summary: Significant losses of citrus fruit can occur following harvest and prior to utilization as a consequence of decay caused by fungal pathogens. Green mold caused by Penicillium digitatum is generally is the most serious postharvest decay of citrus worldwide. Currently, fungicides are applied to citrus fruit following harvest to reduce losses caused by green mold. However, concerns regarding the effects of fungicide treatments on human health, the environment, and the potential for resistance necessitate the development of biorational treatments for decay control. Bacillus subtilis is a soil microorganism that produces compounds know as cyclic lipopeptides. Cyclic lipopeptides have been shown to reduce green mold decay of citrus, but their mechanism of action is unknown. Our hypothesis was that cyclic lipopeptides induce plant defensive responses which are involved in the inhibition of decay. Our objective was to determine if cyclic lipopetides produced by Bacillus subtilis induce defense responses in citrus fruit. Three cyclic lipopetides, fengicin, surfactin, and iturin A were purified from Bacillus subtilis. The three cyclic lipopetides were applied to citrus fruit either alone or in combination with Penicillium digitatum. Following treatment, levels of messenger RNA coding for the defense-related enzymes chitinase, glucanase, peroxidase and lipoxygenase and activity of each enzyme were determined. We found that fengycin caused a significant increase in the level of glucanase messenger RNA and surfactin increased the levels of lipoxygenase and peroxidase transcripts. Fengycin in combination with itruin A or with surfactin had synergistic effects on the abundance of chitinase and glucanase transcripts. Activities of glucanase peroxidase, and lipoxygenase followed trends similar to those of gene expression, however, changes in chitinase activity were not observed. Results of this research indicate that Bacillus subtilis cyclic lipopeptides can induce defense responses in citrus fruit that may contribute to their effect on decay inhibition.
Technical Abstract: Effects of cyclic lipopeptides obtained from B. subtilis ABS-S14 on eliciting defense-related gene transcription and activity of defense-related enzymes glucanase (GLU), chitinase (CHI), peroxidase (POX) and lipoxygenase (LOX) in Citrus sinensis cv. Valencia fruit were determined. The maximum level of GLU transcripts induced in fruit treated with fengycin was significantly greatest among treatments at 48 h. Surfactin enhanced the LOX and POX transcripts. In parallel, corresponding enzyme activities were correlated with changes in gene expression observed in fruit inoculated with P. digitatum following treatment with individual CLPs. Synergistic effects of fengycin and iturin A; fengycin and surfactin were shown in gene transcript of GLU and CHI, respectively, and surfactin induced 24 POX and LOX gene expression of citrus flavedo without pathogen infection. These results suggest that fengycin and surfactin act as elicitors of defense-related gene expression in “Valencia” fruit following infection.