Efficient genome editing using endogenous U6 snRNA promoter-driven CRISPR/Cas9 sgRNA in Sclerotinia sclerotiorum

Characterization of SsHog1 and Shk1 Using Efficient Gene Knockout Systems through Repeated Protoplasting and CRISPR/Cas9 Ribonucleoprotein Approaches in Sclerotinia sclerotiorum

Sclerotinia sclerotiorum is the causal agent of sclerotinia stem rot in over 400 plant species. In a previous study, the group III histidine kinase gene of S. sclerotiorum (Shk1) revealed its involvement in iprodione and fludioxonil sensitivity and osmotic stress. To further investigate the fungicide sensitivity associated with the high-osmolarity glycerol (HOG) pathway, we functionally characterized SsHog1, which is the downstream kinase of Shk1. To generate knockout mutants, split marker transformation combined with a newly developed repeated protoplasting method and CRISPR/Cas9 ribonucleoprotein (RNP) delivery approach were used. The pure SsHog1 and Shk1 knockout mutants showed reduced sensitivity to fungicides and increased sensitivity to osmotic stress. In addition, the SsHog1 knockout mutants demonstrated reduced virulence compared to Shk1 knockout mutants and wild-type. Our results indicate that the repeated protoplasting method and RNP approach can generate genetically pure homokaryotic mutants and SsHog1 is involved in osmotic adaptation, fungicide sensitivity, and virulence in S. sclerotiorum.

Genome editing in the edible fungus Poria cocos using CRISPR-Cas9 system integrating genome-wide off-target prediction and detection

Poria cocos is an important edible and medicinal fungus with a long history. However, the lack of adequate genetic tools has hindered molecular genetic research and the genetic modification of this species. In this study, the endogenous U6 promoters were identified by mining data from the P. cocos genome, and the promoter sequence was used to construct a sgRNA expression vector pFC332-PcU6. Then, the protoplast isolation protocol was developed, and the sgRNA-Cas9 vector was successfully transformed into the cells of P. cocos via PEG/CaCl2-mediated transformation approach. Off-target sites were genome-widely predicted and detected. As a result, the target marker gene ura3 was successfully disrupted by the CRISPR-Cas9 system. This is the first report of genome editing in P. cocos using CRISPR-Cas9 system integrating genome-wide off-target prediction and detection. These data will open up new avenues for the investigation of genetic breeding and commercial production of edible and medicinal fungus.

A Forward Genetic Screen in Sclerotinia sclerotiorum Revealed the Transcriptional Regulation of Its Sclerotial Melanization Pathway

Most plant fungal pathogens that cause worldwide crop losses are understudied, due to various technical challenges. With the increasing availability of sequenced whole genomes of these non-model fungi, effective genetic analysis methods are highly desirable. Here, we describe a newly developed pipeline, which combines forward genetic screening with high-throughput next-generation sequencing to enable quick gene discovery. We applied this pipeline in the notorious soilborne phytopathogen Sclerotinia sclerotiorum and identified 32 mutants with various developmental and growth deficiencies. Detailed molecular studies of three melanization-deficient mutants provide a proof of concept for the effectiveness of our method. A master transcription factor was found to regulate melanization of sclerotia through the DHN (1,8-dihydroxynaphthalene) melanin biosynthesis pathway. In addition, these mutants revealed that sclerotial melanization is important for sclerotia survival under abiotic stresses, sclerotial surface structure, and sexual reproduction. Foreseeably, this pipeline can be applied to facilitate efficient in-depth studies of other non-model fungal species in the future.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.