Progress 10/01/17 to 09/30/20
Outputs
Target Audience:The target audience is the general research community including NC members and participants at the Asilomar Fungal Genetics and American Phytopathological Society meetings. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This was a difficult year to COVID-19 and precluded travel to meetings. Still, all of my student presented their work at a local meeting by zoom. Also, my student Nick Raffa graduated in Dec 2020 and has started a job with industry. How have the results been disseminated to communities of interest?Yes, one paper was published and there are two more in preparation. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
We continue to examine the role of fungal:bacterial communities on mycotoxin synthesis. We find that when bacteria and fungi encounter each other, mycotoxin synthesis by fungi can either be induced (putative protection for fungus) or repressed (putative advantage for bacterium). This has now changed our concept of mycotoxin production in crops. We have published some of this work (J of Fungi.). We are working on (i) how bacteria may survive in fungi and if mycotoxin production alters this survival and if (ii) patulin synthesis by the post-harvest pathogen Pencillium expansum is in response to competition with other microbes found in apple orchards or on the apple.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Steffan B, Venkatesh N, Keller, NP (2020) Lets Get Physical: Bacterial-Fungal Interactions and Their Consequences in Agriculture and Health. J Fungi. 6(4):E243. doi: 10.3390/jof6040243.
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Progress 10/01/18 to 09/30/19
Outputs
Target Audience:The target audience is the general research community including NCCC members and participants at the Asilomar Fungal Genetics and American Phytopathological Society meetings. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Both students, Nandhitha Venkatesh and Nicholas Raffa, went to the 2019 Asilomar Fungal Genetic meeting (March) this past year to present their research. Both students are mentoring undergraduate students. How have the results been disseminated to communities of interest?Yes, to the attendees at the Asilomar Fungal Genetic meeting. What do you plan to do during the next reporting period to accomplish the goals?We are interested in understanding the mechanisms leading to fungal:bacterial cross talk and the ecological significance of this cross talk. We are focused on elucidating the molecules/genes that allow bacteria to enter fungi and how this entry impacts both fungal and bacterial survival.
Impacts
What was accomplished under these goals?
We have gained tremendous insight into the role of fungal:bacterial communities on mycotoxin synthesis. We find that when bacteria and fungi encounter each other, mycotoxin synthesis by fungi can either be induced (putative protection for fungus) or repressed (putative advantage for bacterium). This has now changed our concept of mycotoxin production in crops. We have published some of this work (Frontiers Microbiology. 10:403. doi: 10.3389/fmicb.2019.00403.). Previous HATCH work showed that, moreover, bacteria can enter inside of pathogenic fungi, a topic we are further exploring (see below). Furthermore, we find that fungal toxins can impede growth of pathogenic bacteria.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Venkatesh N, Keller NP (2019) Mycotoxins in conversation with bacteria, fungi and plants. Frontiers Microbiology. 10:403. doi: 10.3389/fmicb.2019.00403.
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Progress 10/01/17 to 09/30/18
Outputs
Target Audience:The target audience is the general research community including NCCC members and participants at the Asilomar Fungal Genetics and American Phytopathological Society meetings. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Four graduate students (one of them supportedthrough Hatch) were involved in these two studies and presented their work at international meetings. How have the results been disseminated to communities of interest?As above, these studies have been presented at professional meetings. What do you plan to do during the next reporting period to accomplish the goals?We will continue to work on these objectives stemming from logical expansions of scientific questions arising from the published works.
Impacts
What was accomplished under these goals?
The ultimate goal is to figure out how fungi make toxins that contaminate our food and feed products. We were able to achieve two major studies that resulted in two publications. 1. Specific goal 1: to find pathways that impactfungal development, aflatoxin production and virulence of A flavus. Aspergillus flavus is a saprophytic soil fungus that poses a serious threat worldwide as it contaminates many food and feed crops with the carcinogenic mycotoxin called aflatoxin. This pathogen persists as sclerotia in the soil which enables fungal survival in harsh environmental conditions. Sclerotia formation by A. flavus depends on successful cell communication and hyphal fusion events. Loss of LaeA, a conserved developmental regulator in fungi, abolishes sclerotia formation in this species whereas overexpression (OE) of laeA results in enhanced sclerotia production. Here we demonstrate that sclerotia loss and inability to form heterokaryons in A. flavusΔlaeA is mediated by homologs of the Neurospora crassa ham (hyphal anastomosis) genes termed hamE-I in A. flavus. LaeA positively regulates ham gene expression and deletion of hamF, G, H, or I phenocopies ΔlaeA as demonstrated by heterokaryon and sclerotia loss and reduced aflatoxin synthesis and virulence of these mutants. Deletion of hamE showed a less severe phenotype. hamE-I homologs are positively regulated by the clock controlled transcription factor ADV-1 in N. crassa. Similarly, the ADV-1 homolog NosA regulates hamE-I expression in A. flavus, is required for sclerotial development and is itself positively regulated by LaeA. We speculate that a putative LaeA>NosA>fusion cascade underlies the previously described circadian clock regulation of sclerotia production in A. flavus. Specific Goal 2: Impacts of the microbiome on mycotoxigenic fungi.Small-molecule signaling is one major mode of communication within the polymicrobial consortium of soil and rhizosphere. While microbial secondary metabolite (SM) production and responses of individual species have been studied extensively, little is known about potentially conserved roles of SM signals in multilayered symbiotic or antagonistic relationships. Here, we characterize the SM-mediated interaction between the plant-pathogenic bacterium Ralstonia solanacearum and the two plant-pathogenic fungi Fusarium fujikuroi and Botrytis cinerea We show that cellular differentiation and SM biosynthesis in F.fujikuroi are induced by the bacterially produced lipopeptide ralsolamycin (synonym ralstonin A). In particular, fungal bikaverin production is induced and preferentially accumulates in fungal survival spores (chlamydospores) only when exposed to supernatants of ralsolamycin-producing strains of R.solanacearum Although inactivation of bikaverin biosynthesis moderately increases chlamydospore invasion by R.solanacearum, we show that other metabolites such as beauvericin are also induced by ralsolamycin and contribute to suppression of R.solanacearum growth in vitro Based on our findings that bikaverin antagonizes R.solanacearum and that ralsolamycin induces bikaverin biosynthesis in F.fujikuroi, we asked whether other bikaverin-producing fungi show similar responses to ralsolamycin. Examining a strain of B.cinerea that horizontally acquired the bikaverin gene cluster from Fusarium, we found that ralsolamycin induced bikaverin biosynthesis in this fungus. Our results suggest that conservation of microbial SM responses across distantly related fungi may arise from horizontal transfer of protective gene clusters that are activated by conserved regulatory cues, e.g., a bacterial lipopeptide, providing consistent fitness advantages in dynamic polymicrobial networks.IMPORTANCE Bacteria and fungi are ubiquitous neighbors in many environments, including the rhizosphere. Many of these organisms are notorious as economically devastating plant pathogens, but little is known about how they communicate chemically with each other. Here, we uncover a conserved antagonistic communication between the widespread bacterial wilt pathogen Ralstonia solanacearum and plant-pathogenic fungi from disparate genera, Fusarium and Botrytis Exposure of Fusarium fujikuroi to the bacterial lipopeptide ralsolamycin resulted in production of the antibacterial metabolite bikaverin specifically in fungal tissues invaded by Ralstonia Remarkably, ralsolamycin induction of bikaverin was conserved in a Botrytis cinerea isolate carrying a horizontally transferred bikaverin gene cluster. These results indicate that horizontally transferred gene clusters may carry regulatory prompts that contribute to conserved fitness functions in polymicrobial environments.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2018
Citation:
Conserved Responses in a War of Small Molecules between a Plant-Pathogenic Bacterium and Fungi.
Spraker JE, Wiemann P, Baccile JA, Venkatesh N, Schumacher J, Schroeder FC, Sanchez LM, Keller NP.
MBio. 2018 May 22;9(3). pii: e00820-18. doi: 10.1128/mBio.00820-18.
- Type:
Journal Articles
Status:
Published
Year Published:
2017
Citation:
Front Microbiol. 2017 Oct 5;8:1925. doi: 10.3389/fmicb.2017.01925. eCollection 2017.
A Cellular Fusion Cascade Regulated by LaeA Is Required for Sclerotial Development in Aspergillus flavus.
Zhao X, Spraker JE, Bok JW, Velk T, He ZM, Keller NP
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