UBC Theses and Dissertations

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UBC Theses and Dissertations

Molecular responses of plants to symbiotic fungi Ribeiro Quitans, Isadora Louise Alves da Costa


Plants and fungi interact in complex ways that can benefit or harm a plant. To better understand how plants defend against pathogens and enhance interactions with beneficial fungi, I used several different approaches to identify genes and pathways involved in these processes. First, I developed a bioinformatics pipeline to search for antimicrobial peptides (AMPs) in public DNA sequence databases. I found 16,870 novel candidate AMPs from 1,003 species, and demonstrated that transcripts of heveins and cyclolinopeptides (CLPs), especially, increased abundance in response to a pathogenic fungus (Fusarium oxysporum f. sp. lini) but not a mutualistic fungus (Rhizoglomus irregulare). Second, I developed an in vitro system to evaluate the effects of the interaction of two mutualistic fungi (Rhizoglomus irregulare and Clonostachys rosea) on flax roots infected by F. oxysporum. I found that both R. irregulare and C. rosea have bio-protective effects against F. oxysporum. R. irregulare also increased flax biomass production, while mitigating the negative effects caused by F. oxysporum on shoot length and biomass. Third, I used RNA-Seq to compare the pre-colonization responses of flax roots to inoculation with R. irregulare or F. oxysporum, separately and in combination. I found distinct classes of genes that responded uniquely to the pathogen and the mutualist. Finally, I tested the activity of flax CLPs, polyamines (PAs), and carbendazim against three pathogenic fungi: F. oxysporum, S. linicola, and Alternaria sp. I found that CLPs and PAs have antifungal activity in vitro against the fungi studied at a concentration range that might be biologically relevant. We suggest that CLPs and PAs should be tested for the mitigation of Alternaria sp. in vivo, since these compounds had better effects on the growth inhibition of this fungus in comparison to a commercial antifungal agent. Together, these data will improve the understanding of mechanisms underlying pathogenicity and mutualism, and will lead to the development of better strategies to control fungal diseases.

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