IMPACT OF FUNGAL SECONDARY METABOLITES ON TRANSCRIPT REGULATION OF FOLSOMIA CANDIDA

Genetic and molecular evidence to support the hypothesis that fungal secondary metabolites play a significant role in protecting the fungi against fungivory is scarce. We investigated the impact of fungal secondary metabolites on transcript regulation of stress related expressed sequence tags (ESTs) of the Collembola Folsomia candida feeding on mixed vs. single diets. Aspergillus nidulans wildtype (WT; Ascomycota) able to produce secondary metabolites including sterigmatocystin (ST) and a knockout mutant with reduced secondary metabolism (A. nidulans ΔLaeA) were combined with the high quality fungus Cladosporium cladosporioides as mixed diets or offered as single diets. We hypothesized that (i) A. nidulans WT triggers more genes associated with stress responses compared to the A. nidulans ΔlaeA strain with suppressed secondary metabolism, (ii) C. cladosporioides causes significantly different transcript regulation than the A. nidulans strains ΔlaeA and WT, and (iii) mixed diets will cause significantly different transcript expression levels than single diets. All three hypotheses are generally supported despite the fact that many functions of the affected ESTs are unknown. The results bring molecular evidence for the existence of a link between fungal secondary metabolites and responses in springtails supporting the hypothesis that fungal secondary metabolites act as a shield against fungivory. Twenty-three day old Folsomia candida were fed ad libitum for five days to fungal cuts respectively Cladosporium cladosporoides, Aspergillus nidulans WT, Aspergillus nidulans ΔLaeA and two mixed diets of C.cladosporoides/A. nidulans WT (mix 1) and C. cladosporoides/A. nudlans ΔLaeA (mix2) respectively. Four biological replicates were used for every treatment and a dye swap was used with the Cy3/Cy5 labels. This resulted in 20 samples which were analysed in 10 hybridisations executed in an interwoven loop design. The C. cladosporoides diet was used as the reference in the data analysis.