The C2H2 Transcription Factor SsZFH1 Regulates the Size, Number, and Development of Apothecia in Sclerotinia sclerotiorum

Transcriptional Activator UvXlnR Is Required for Conidiation and Pathogenicity of Rice False Smut Fungus Ustilaginoidea virens

Transcription factors play critical roles in diverse biological processes in fungi. XlnR, identified as a transcriptional activator that regulates the expression of the extracellular xylanase genes in fungi, has not been extensively studied for its function in fungal development and pathogenicity in rice false smut fungus Ustilaginoidea virens. In this study, we characterized UvXlnR in U. virens and established that the full-length, N-terminal, and C-terminal forms have the ability to activate transcription. The study further demonstrated that UvXlnR plays crucial roles in various aspects of U. virens biology. Deletion of UvXlnR affected growth, conidiation, and stress response. UvXlnR mutants also exhibited reduced pathogenicity, which could be partially attributed to the reduced expression of xylanolytic genes and extracellular xylanase activity of U. virens during the infection process. Our results indicate that UvXlnR is involved in regulating growth, conidiation, stress response, and pathogenicity.

The Transcription Factor SsZNC1 Mediates Virulence, Sclerotial Development, and Osmotic Stress Response in Sclerotinia sclerotiorum

Sclerotinia sclerotiorum is a fungal pathogen with a broad range of hosts, which can cause diseases and pose a great threat to many crops. Fungal-specific Zn2Cys6 transcription factors (TFs) constitute a large family prevalent among plant pathogens. However, the function of Zn2Cys6 TFs remains largely unknown. In this study, we identified and characterized SsZNC1, a Zn2Cys6 TF in S. sclerotiorum, which is involved in virulence, sclerotial development, and osmotic stress response. The expression of SsZNC1 was significantly up-regulated in the early stages of S. sclerotiorum infection on Arabidopsis leaves. The target deletion of SsZNC1 resulted in reduced virulence on Arabidopsis and oilseed rape. In addition, sclerotial development ability and growth ability under hyperosmotic conditions of SsZNC1 knockout transformants were reduced. A transcriptomic analysis unveiled its regulatory role in key cellular functions, including cellulose catabolic process, methyltransferase activity, and virulence, etc. Together, our results indicated that SsZNC1, a core regulatory gene involved in virulence, sclerotial development and stress response, provides new insight into the transcription regulation and pathogenesis of S. sclerotiorum.

Heritability and gene functions associated with sclerotia formation of Rhizoctonia solani AG-7 using whole genome sequencing and genome-wide association study

Sclerotia are specialized fungal structures formed by pigmented and aggregated hyphae, which can survive under unfavourable environmental conditions and serve as the primary inocula for several phytopathogenic fungi including Rhizoctonia solani. Among 154 R. solani anastomosis group 7 (AG-7) isolates collected in fields, the sclerotia-forming capability regarding sclerotia number and sclerotia size varied in the fungal population, but the genetic makeup of these phenotypes remained unclear. As limited studies have focused on the genomics of R. solani AG-7 and the population genetics of sclerotia formation, this study completed the whole genome sequencing and gene prediction of R. solani AG-7 using the Oxford NanoPore and Illumina RNA sequencing. Meanwhile, a high-throughput image-based method was established to quantify the sclerotia-forming capability, and the phenotypic correlation between sclerotia number and sclerotia size was low. A genome-wide association study identified three and five significant SNPs associated with sclerotia number and size in distinct genomic regions, respectively. Of these significant SNPs, two and four showed significant differences in the phenotypic mean separation for sclerotia number and sclerotia size, respectively. Gene ontology enrichment analysis focusing on the linkage disequilibrium blocks of significant SNPs identified more categories related to oxidative stress for sclerotia number, and more categories related to cell development, signalling and metabolism for sclerotia size. These results indicated that different genetic mechanisms may underlie these two phenotypes. Moreover, the heritability of sclerotia number and sclerotia size were estimated for the first time to be 0.92 and 0.31, respectively. This study provides new insights into the heritability and gene functions related to the development of sclerotia number and sclerotia size, which could provide additional knowledge to reduce fungal residues in fields and achieve sustainable disease management.