Transcriptomic Responses of Fusarium verticillioides to Lactam and Lactone Xenobiotics

Authors: GAO, MINGLU - University Of Georgia; Gold, Scott; GU, XI - University Of Georgia; Satterlee, Tim; Duke, Mary; Scheffler, Brian; Glenn, Anthony - Tony

Submitted to: Frontiers in Fungal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2022
Publication Date: 6/20/2022
Citation: Gao, M., Gold, S.E., Gu, X., Satterlee, T.R., Duke, M.V., Scheffler, B.E., Glenn, A.E. 2022. Transcriptomic Responses of Fusarium verticillioides to Lactam and Lactone Xenobiotics. Frontiers in Fungal Biology. https://doi.org/10.3389/ffunb.2022.923112.
DOI: https://doi.org/10.3389/ffunb.2022.923112

Interpretive Summary: Even after decades of drug discovery, nature still has much to offer in terms of new antimicrobial compounds. Many of the known antibacterial and antifungal chemical compounds have structural features defining them as either lactams or lactones. Likewise, many bacteria and fungi produce lactamase and lactonase enzymes that degrade these antimicrobials and protect the microbes from these inhibitory compounds. To identify the underlying genes responsible for production of these and other enzymes, we conducted a series of studies exposing the mycotoxin-producing fungus Fusarium verticillioides to four different structurally related lactam and/or lactone compounds. A method called RNA-Seq was used to identify the F. verticillioides genes differentially expressed in response to these chemicals. By identifying the differentially expressed genes that are shared or unique to each compound, we hoped to identify potentially new detoxification strategies and perhaps new targets for chemically controlling the ability of this fungus to infect corn and contaminate kernels with mycotoxins. The expression data are presented in detail, and new gene targets for subsequent study are discussed.

Technical Abstract: The important cereal crops of maize, rye, and wheat constitutively produce precursors to 2-benzoxazolinone, a phytochemical having antifungal effects towards many Fusarium species. However, Fusarium verticillioides can tolerate 2-benzoxazolinone by converting it into non-toxic metabolites through the synergism of two previously identified gene clusters, FDB1 and FDB2. Inspired by the induction of these two clusters upon exposure to 2-benzoxazolinone, RNA sequencing experiments were carried out by challenging F. verticillioides individually with 2-benzoxazolinone and three related chemical compounds, 2-oxindole, 2-coumaranone, and chlorzoxazone. Chlorzoxazone is a chlorinated 2-benzoxazolinone (5-chloro-2-benzoxazolinone). These compounds all contain lactam and/or lactone moieties, and transcriptional analysis provided inferences regarding the degradation of such lactams and lactones. Besides induction of FDB1 and FDB2 gene clusters, four additional clusters were identified as induced by 2-benzoxazolinone exposure, including a cluster thought to be responsible for biosynthesis of pyridoxine (vitamin B6), a known antioxidant providing tolerance to reactive oxygen species. Three putative gene clusters were identified as induced by challenging F. verticillioides with 2-oxindole, two with 2-coumaranone, and two with chlorzoxazone. Interestingly, 2-benzoxazolinone and 2-oxindole each induced two specific gene clusters with similar composition of enzymatic functions. Exposure to 2-coumranone elicited the expression of the fusaric acid biosynthetic gene cluster. Another gene cluster that may encode enzymes responsible for degrading intermediate catabolic metabolites with carboxylic ester bonds was induced by 2-benzoxazolinone, 2-oxindole, and chlorzoxazone. Also, the induction of a dehalogenase encoding gene during chlorzoxazone exposure suggested its role in the removal of the chlorine atom. Together, this work identifies genes and putative gene clusters responsive to the 2-benzoxazolinone-like compounds with metabolic inferences, and interesting targets for future functional analyses are discussed.