Global transcriptomic responses orchestrate difenoconazole resistance in Penicillium spp. causing blue mold of stored apple fruit

Authors: LITCHNER, FRANZ - Oak Ridge Institute For Science And Education (ORISE); Gaskins, Verneta; COX, KERIK - Cornell University; Jurick, Wayne

Submitted to: BioMed Central (BMC) Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2020
Publication Date: 8/24/2020
Citation: Litchner, F.J., Gaskins, V.L., Cox, K., Jurick II, W.M. 2020. Global transcriptomic responses orchestrate difenoconazole resistance in Penicillium spp. causing blue mold of stored apple fruit. BioMed Central (BMC) Genetics. https://doi.org/10.1186/s12864-020-06987-z.
DOI: https://doi.org/10.1186/s12864-020-06987-z

Interpretive Summary: Antimicrobial resistance (AMR) is a widespread problem that occurs in medical, veterinary, and agriculturally relevant microbes upon repeated use of antibiotics and fungicides. Tactics to abate AMR have been slow to advance due to the lack of fundamental knowledge on how these pathogens develop. AMR interferes with agricultural product quality in apple fruit, which are stored for 6 to 12 months, and are highly vulnerable to rot without fungicide application. These fungi cause product loss, reduce fruit quality, and produce mycotoxins (e.g. patulin) that impact human health. Recently, difenoconazole-resistant Penicillium spp. isolates causing apple blue mold have been detected in packing and storage environments in the United States. Hence, we sought to compare the genetic changes in a fungicide-resistant and sensitive blue mold isolates. We found differences in the expression of genes involved in pump activation and metabolism that will be used to design detection tools for monitoring storage and packinghouse environments.

Technical Abstract: Blue mold decay is a globally important and economically impactful postharvest problem of apple caused by multiple Penicillium spp. There are currently four postharvest fungicides registered for blue mold control, and some isolates have developed resistance manifesting in decay on fungicide-treated fruit during storage. Critical information on fungicide resistance mechanisms have not been explored in this fungus via a transcriptomic approach nor have they been coupled with in vitro studies to provide biologically relevant information to confirm new resistance mechanisms. We have conducted a comparative transcriptomic study by exposing a naturally difenoconazole (DIF) resistant (G10) and sensitive (P11) blue mold isolates to technical grade DIF, an azole ingredient in the postharvest fungicide Academy (Syngenta Crop Protection, LLC). Dynamic changes in gene expression patterns were observed encompassing candidates involved in active efflux, metabolism, and signal transduction between the resistant and sensitive isolates. Amongst these were cytochrome P450 monoxygenase, in which 3 isoforms were detected and activated in both sensitive and resistant strains upon DIF treatment. Active efflux pumps were coordinately regulated in the resistant isolate and were shown to mediate the global resistance mechanism as their inhibition reversed the DIF-resistant phenotype in vitro. Our results support the observation that global changes at the transcriptional level are a biologically significant contributor of the DIF resistance mechanism in Penicillium spp. While the dogma of CYP51 overexpression is supported in the resistant isolate, our studies shed light on additional mechanisms on a global scale in Penicillium spp. These new findings broaden our fundamental understanding of azole fungicide resistance in fungi, which has identified multiple genetic targets, that can be used for the detection, management, and abatement of difenoconazole-resistant blue mold isolates during storage.