Program Book - 27th Fungal Genetics Conference

CONCURRENT SESSION ABSTRACTSEffect of antifungal resistance on virulence of Candida spp. L. Vale-Silva, A. Lohberger, D. Sanglard. Inst Microbiology, Univ Lausanne and Univ HospCenter, Lausanne, VD, Switzerland.Our laboratory has been involved in the understanding of mechanisms of antifungal resistance in fungal pathogens. While resistance is beneficial to fungiin the presence of antifungals both in vitro and in vivo, resistance mechanisms have some impact on the ability of fungal pathogens to propagate in thehost and cause disease. We have addressed this question with two pathogens, C. albicans (Ca) and C. glabrata (Cg). Our studies have focused on resistanceto azoles, which are widely used compounds. In Cg, azole resistance in clinical isolates is almost exclusively mediated by ABC transporters via gain offunction (GOF) mutations in the transcription factor (TF) CgPDR1. We observed that development of azole resistance in Cg was correlated with gain ofvirulence and fitness in animal models as compared to susceptible isolates. Recent results suggest that ABC transporters (especially CgCDR1) participate tothis phenotype. In further studies on interactions of Cg with murine bone marrow-derived macrophages (BMDM), we found that the GOF mutant was ableto evade phagocytosis as compared to a matched susceptible isolate. This effect was a consequence of impaired adhesion. This suggests that themechanism behind escape from phagocytosis was rather based on decreased recognition and/or adhesion by host macrophages. GOF mutations inCgPDR1 may thus allow Cg to evade the host’s innate immune response, which may in turn contribute to increased virulence. In Ca azole resistance ismediated by mutations in TF and in azole targets. GOF mutations in the three different activators including TAC1, MRR1 and UPC2 regulate specific subclassesof drug resistance genes belonging to ABC-transporters, major facilitators and azole targets, respectively. We have constructed sets of isogenicstrains lacking or carrying each GOF mutations in these TF and addressed their effect on virulence and tissue colonization in animal models. The presenceof GOF mutations in TAC1 and MRR1 had a neutral effect on virulence and ability to colonize host tissues. A UPC2 GOF mutation was negatively affectingvirulence and tissue colonization, which suggests that UPC2 activity generates fitness costs in Ca. Our results therefore highlight that the costs ofresistance mechanisms on virulence are depending on the fungal species and the type of resistance mechanism.From enzyme to fungal development or how sdhB mutations impact respiration, fungicide resistance and fitness in the grey mold agent Botrytiscinerea. Anais Laleve 1 , Anne-Sophie Walker 1 , Stephanie Gamet 2 , Valerie Toquin 2 , Daniele Debieu 1 , Sabine Fillinger 1 . 1) BIOGER, INRA, Thiverval-Grignon,France; 2) BAYER SAS, Bayer CropScience, Lyon, France.Respiration inhibitor fungicides are widely used to control fungal diseases on multiple crops. The succinate dehydrogenase inhibitors (SDHIs) are amongthe latest introduced molecules against the grey mold agent Botrytis cinerea on grapevine. We have recently isolated and characterized B. cinerea fieldstrains resistant to the SDHIs. Most of the strains harbor one single mutation in the succinate dehydrogenase subunit gene, sdhB affecting the ubiquinonebindingpocket. In this study we have introduced these mutations into a B. cinerea wild-type strain (B05.10) in order to evaluate the impact of eachmutation on SDH- and respiratory activity and inhibition by SDHIs from different chemistries. We also analyzed several parameters of B. cinerea’s life cycleto assess the fitness cost associated with the resistance mutation. Our results show a strict correlation between the sdhB mutation and the resistancespectra to SDHIs. These resistances can be fully explained by the affinities of the SDHIs to its modified target enzyme. Four out of the seven sdhB alleles ledto significantly reduced SDH activity and, in three cases (H272L, N230I, P225L), to reduced respiration rates. Concerning the fungal biology, we testedmycelial growth and sclerotia production on different media and temperatures, conidia production and germination, resistance to oxidative stress and ROSproduction, as well as pathogenicity on tomato and bean leaves. All mutants were affected for at least one parameter. However, fitness parameters ofmutants sdhB H272R and sdhB P225L showed the strongest modifications among all strains, e.g., reduced pathogenicity, strongly reduced conidia- and sclerotiaproduction(H272R). A clear correlation between fitness and respiration on one hand, fitness and allele frequency among natural populations on the other,is not yet obvious. However, our results in terms of resistance spectra and fitness parameters should help defining more efficient treatment strategiesagainst grey mold.Deciphering fungicide resistance mechanisms in phytopatogenic fungi, towards an assessment of resistance risk in new active ingredient research.Gabriel Scalliet 1* , Andreas Mosbach 1 , Diana Steinhauer 1 , Edel Dominique 1 , Robert Dietrich 2 . 1) Disease Control, Syngenta Crop Protection Munchwilen AG,Stein, Switzerland; 2) Syngenta Biotechnology, Inc 3054 Cornwallis Rd. Research Triangle Park, NC 27709.Resistance to crop protection fungicides can lead to a rapid loss of efficacy in the field. This is a major threat for the sustainability of our products. Anearly assessment is required in order to define best recommendations in product usage but also guide our choice in developing novel active ingredients. Inaddition to monitoring the situation for marketed fungicides, we are conducting early assessments for new active ingredients which include resistancegeneration, mode of resistance identification and fitness penalty determination. High throughput sequencing has become key for a rapid identification ofresistance mechanisms both for novel fungicides but also to holder chemistries for which the resistance mechanisms were so far not confirmed. A fewexamples will be discussed.27th Fungal Genetics Conference | 83