Functional analysis of polyketide synthases in the biocontrol fungus Clonosthachys rosea

Abstract: Clonostachys rosea, a filamentous ascomycete, is a well-known biological control agent (BCA) against a wide range of plant pathogenic fungi. Genome sequencing revealed that C. rosea strain IK726 possess 32 genes encoding for polyketide synthases (PKS), which is significantly higher than the more studied biocontrol fungi Trichoderma. During our previous study, we showed a culture medium dependent antagonistic effect of C. rosea against plant pathogenic fungi Alternaria alternata, Botrytis cinerea, Fusarium graminearum, and Rhizoctonia solani. Furthermore, we showed a positive correlation between pks gene expression and antagonism in C. rosea. The aim of the present study was to i) analyse the expression of pks genes in C. rosea under developmental stages and during C. rosea interaction with prey fungi; and ii) to characterize the biological function of one or few polyketide synthases in C. rosea by generating gene deletion mutants. The expression pattern of pks in C. rosea during pigmentation and during antagonistic interaction with plant pathogenic fungi B. cinerea and F. graminearum was investigated using quantitative polymerase chain reaction. Our results showed that 19 pks in C. rosea were significantly induced during pigmentation compared to the non-pigmented control. Our result also showed induced expression of 18 pks during C. rosea and B. cinerea interaction (Cr-Bc) compared to C. rosea self-interaction (Cr-Cr) or C. rosea and F. graminearum interaction (Cr-Fg), and 7 pks during Cr-Fg compared to Cr-Cr or Cr-Bc. Phenotypic analyses of C. rosea wild-type (WT), pks22 and pks29 gene deletion mutants (Δpks22 and Δpks29) demonstrate that Δpks22 had a significant reduction (P ≤ 0.004) in mycelial growth rate in comparison to WT. However, no significant difference in antagonism against B. cinerea or F. graminearum between WT and Δpks22 was found. On the other hand, deletion of pks29 resulted in no significant difference in growth rate but reduction (P ≤ 0.011) in antagonistic ability against B. cinerea or F. graminearum in C. rosea. These data show that the PKS is important for normal growth and development, and antagonism in C. rosea.