Transgene induced co-suppression during vegetative growth in Cryptococcus neoformans

Area of Science:

• Molecular Biology
• Genetics
• Mycology

Background:

• Homology-dependent gene silencing is observed across diverse organisms.
• Previous work showed high gene silencing during mating in Cryptococcus neoformans, but low frequency during vegetative growth.

Purpose of the Study:

• To investigate a robust asexual co-suppression phenomenon in Cryptococcus neoformans.
• To elucidate the mechanisms underlying transgene-induced gene silencing during vegetative growth.

Main Methods:

• Ectopic integration of a cpa1::ADE2 transgene into the Cryptococcus neoformans genome.
• Detection of CPA1-derived small interfering RNAs (siRNAs).
• Assessment of RNA interference (RNAi) pathway component requirements (Rdp1, Ago1, Dcr2) and replication protein A (RPA) involvement.

Main Results:

• Introduction of the cpa1::ADE2 transgene led to high-frequency silencing of endogenous CPA1 and CPA2 genes.
• Silencing efficiency correlated with transgene copy number, reaching ~90% with >25 copies.
• RNAi pathway components and RPA were essential for this asexual co-suppression.
• Silencing of the ADE2 gene occurred less frequently than CPA1/2, indicating copy number is not the sole factor.

Conclusions:

• A robust asexual co-suppression process, mediated by RNAi and dependent on RPA, operates during Cryptococcus neoformans vegetative growth.
• This phenomenon shares mechanistic similarities with quelling in Neurospora crassa.
• Transgene copy number and other factors influence silencing efficiency.