Characterizing the role of RNA silencing components in Cryptococcus neoformans

Abstract

SummaryThe RNA interference (RNAi) mediated by homology-dependent degradation of the target mRNA with small RNA molecules plays a key role in controlling transcription and translation processes in a number of eukaryotic organisms. The RNAi machinery is also evolutionarily conserved in a wide variety of fungal species, including pathogenic fungi. To elucidate the physiological functions of the RNAi pathway in Cryptococcus neoformans that causes fungal meningitis, here we performed genetic analyses for genes encoding Argonaute (AGO1 and AGO2), RNAdependent RNA polymerase (RDP1), and Dicers (DCR1 and DCR2) in both serotype A and D C. neoformans. The present study shows that Ago1, Rdp1, and Dcr2 are the major components of the RNAi process occurring in C. neoformans. However, the RNAi machinery is not involved in regulation of production of two virulence factors (capsule and melanin), sexual differentiation, and diverse stress response. Comparative transcriptome analysis of the serotype A and D RNAi mutants revealed that only modest changes occur in the genome-wide transcriptome profiles when the RNAi process was perturbed. Notably, the serotype D rdp1Δ mutants showed an increase in transcript abundance of active retrotransposons and transposons, such as T2 and T3, the latter of which is a novel serotype D-specific transposon of C. neoformans. In a wild type background both T2 and T3 were found to be weakly active mobile elements, although we found no evidence of Cnl1 retrotransposon mobility. In contrast, all three transposable elements exhibited enhanced mobility in the rdp1Δ mutant strain. In conclusion, the RNAi pathway plays an important role in controlling transposon activity and genome integrity of C. neoformans.

Genome Comparison of Barley and Maize Smut Fungi Reveals Targeted Loss of RNA Silencing Components and Species-Specific Presence of Transposable Elements

“…U. hordei (and S. reilianum, but not U. maydis) contains the necessary genes Chp1-, Chp2-, and Swi6-like needed for this mechanism (see Supplemental Table 3 online). Direct control of TE activity by RNAi in fungi has also been demonstrated in Saccharomyces species, where DICER and ARGONAUTE proteins silence endogenous retrotransposons (Drinnenberg et al, 2009), and in Cryptococcus neoformans, where RNAi controls TE activity during sexual development (Janbon et al, 2010;Wang et al, 2010). Therefore, fungi seem to use RNAi for protection against TEs similar to other eukaryotes.…”

A PKS gene, pks-1, is involved in chaetoglobosin biosynthesis, pigmentation and sporulation in Chaetomium globosum

“…Recently, RNA interference (RNAi) has emerged as a powerful tool for gene targeting in fungi [26][27][28]. Conventional RNAi machinery components, including the RNA-dependent RNA polymerase, Argonaut proteins and Dicers are conserved in some fungi, e.g., Cryptococcus neoformans [29], Bipolaris oryzae [30], Aspergillus and Fusarium Species [31] and Cochliobolus sativus [32]. However, its application in C. globosum has not been reported.…”

3 RNAi Function and Diversity in Fungi

“…Since one role of RNAi is to control transposable elements, the loss of RNAi allows an increased movement of transposons. This has been observed in C. gatti (Janbon et al 2010;Wang et al 2010Wang et al , 2013. Loss of RNAi could conceivably contribute to a hypermutator phenotype which is advantageous in organisms required to adapt rapidly to new environments.…”