Simplified and effective RNA interference and CRISPR-Cas9 systems for Cryptococcus neoformans

Abstract

The 3,4-dihydroxyphenylalanine (DOPA) melanin is one of important virulence factors for Cryptococcus neoformans, which may trigger immune responses in the host. It is worth exploring the genetic function of C. neoformans, by which we may derive more antifungal strategies. Therefore, we established two systems that were constructed quickly and easily for the knock-down/knock-out of LAC1 gene: RNA interference (RNAi) and clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9. The RNAi system used pSilencer 4.1-CMV neo plasmid and short hairpin RNA to realize the effective transcriptional suppression. The CRISPR-Cas9 system used the PNK003 vectors to obtain a stable albino mutant strain. The results of phenotype, qRT-PCR, Transmission Electron Microscope (TEM) and spectrophotometry were used to assess the ability of melanin production. As a result, the RNAi system displayed attenuation of transcriptional suppression when the transformants continuously passed on new plates. However, the transcriptional suppression of long loop in short hairpin RNA were more powerful and lasted longer. The CRISPR-Cas9 system constructed an albino strain completely without the ability to produce melanin. Considering the weakening of transcriptional suppression, we recommend using a long loop for the RNAi system and 1st or 2nd passage of knockdown strains for the subsequent studies. Besides, the different capacities of melanin production might be useful for exploring the linear relation between melanin and immunoreaction of the host. In addition, we recommend applying the PNK003 vectors to other serotypes of C. neoformans for quick screening of possible trait-regulating genes because of its easy construction and valid knockout effect.