Transcriptomic analysis to identify candidate genes conferring gossypol tolerance in Fusarium oxysporum f. sp. vasinfectum

Abstract

Fusarium oxysporium f.sp vasinfectum (Fov) is a soilborne filamentous fungus that causes vascular wilt on cotton. In response to pathogens such as Fov, cotton plants produce the phytoalexin gossypol as a defense mechanism. This research aims to explore the molecular mechanism(s) utilized by Fov to tolerate the antimicrobial action of gossypol during infection and colonization of cotton. Candidate genes that could be responsible for gossypol tolerance were identified through RNA sequencing. Four RNA samples were extracted from germlings of a highly virulent race 4 genotype Fov isolate that was grown in minimal medium in the presence of 80 μg/mL of gossypol for 1, 2, and 4 hours as well as untreated control. RNA-seq data showed upregulation of ABC and major facilitator transporters, fungal transcription factors, cytochrome P450s, and several classes of dehydrogenases when compared with transcripts isolated from the non-treated Fov RNA sample. KEGG pathway analysis identified genes involved in various metabolic pathways, including the biosynthesis of secondary metabolites and antibiotics. The RNA-seq data was validated through RT-qPCR where out of the selected 29 upregulated genes, 16 were significantly expressed through a paired t-test. Even though some genes were not significantly expressed, the expression was increased 70 to 240-fold for at least a single time point. Importantly, candidate genes and gene classes that could be involved in conferring gossypol tolerance were identified Including a beta lactamse, a tannase, several dehydrogenases, transcription factors, cytochrome P450s, and multiple ABC and major facilitator superfamily transporters. Collectively, these findings provide a framework for further investigation into Fov virulence and the mechanisms underlying gossypol tolerance.

Keywords: cotton, Fusarium oxysporum f.sp. vasinfectum, gossypol, tolerance