The Coupling Between Cell Wall Integrity Mediated by MAPK Kinases and SsFkh1 Is Involved in Sclerotia Formation and Pathogenicity of Sclerotinia sclerotiorum

Abstract

The plant pathogenic fungus Sclerotinia sclerotiorum can survive on a wide range of hosts and cause significant losses on crop yields. FKH, a forkhead box (FOX)-containing protein, functions to regulate transcription and signal transduction. As a transcription factor (TF) with multiple biological functions in eukaryotic organisms, little research has been done on the role of FKH protein in pathogenic fungi. SsFkh1 encodes a protein which has been predicted to contain FOX domain in S. sclerotiorum. In this study, the deletion mutant of SsFkh1 resulted in severe defects in hyphal development, virulence, and sclerotia formation. Moreover, knockout of SsFkh1 lead to gene functional enrichment in mitogen-activated protein kinase (MAPK) signaling pathway in transcriptome analysis and SsFkh1 was found to be involved in the maintenance of the cell wall integrity (CWI) and the MAPK signaling pathway. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that SsFkh1 interacts with SsMkk1. In addition, we explored the conserved MAPK signaling pathway components, including Bck1, Mkk1, Pkc1, and Smk3 in S. sclerotiorum. ΔSsmkk1, ΔSspkc1, ΔSsbck1, and ΔSssmk3knockout mutant strains together with ΔSsmkk1com, ΔSspkc1com, ΔSsbck1com, and ΔSssmk3com complementation mutant strains were obtained. The results indicated that ΔSsmkk1, ΔSspkc1, ΔSsbck1, and ΔSssmk3 displayed similar phenotypes to ΔSsfkh1 in sclerotia formation, compound appressorium development, and pathogenicity. Taken together, SsFkh1 may be the downstream substrate of SsMkk1 and involved in sclerotia formation, compound appressorium development, and pathogenicity in S. sclerotiorum.

SsAGM1-Mediated Uridine Diphosphate-N-Acetylglucosamine Synthesis Is Essential for Development, Stress Response, and Pathogenicity of Sclerotinia sclerotiorum

“…Cell wall integrity was involved in the formation of sclerotia ( Cong et al, 2022 ), and SsAGM1 was involved in the maintenance of cell wall integrity and chitin synthesis. This suggested that SsAGM1 may be involved in vegetative growth, especially the formation of sclerotia.…”

“…Recent studies have shown that cell wall integrity was related closely to vegetative growth and sclerotia formation of S. sclerotiorum . In S. sclerotiorum , SsFkh1 is involved in the maintenance of cell wall integrity, and SsFkh1 deletion mutants are severely defective in hyphal growth and sclerotia formation ( Cong et al, 2022 ). SsAGM1 was required for chitin synthesis, and it contributed to maintain the integrity of the cell wall.…”

Sclerotinia sclerotiorum (Lib.) de Bary: Insights into the Pathogenomic Features of a Global Pathogen

“…According to recent research, vegetative development and sclerotial production in S. sclerotiorum are intimately tied to cell wall integrity. SsFkh1 contributes to cell wall integrity, and the deletion mutants are significantly deficient in hyphal development and sclerotial formation [ 96 ]. SsAGM1 has been isolated from several fungi, identified as necessary for chitin production, and known to play a role in preserving the integrity of cell wall [ 97 , 98 ].…”

A MAP kinase cascade broadly regulates development and virulence ofSclerotinia sclerotiorumand can be targeted by HIGS for disease control

“…Although parallel S. cerevisiae MAPK cascades in S. sclerotiorum were identified through homology comparison with yeast, few were characterized molecularly (Hegedus et al, 2016). The disruption of the cell wall integrity MAPK pathway components, including Pkc1, Bck1, Mkk1, and Smk3, not only led to decreased cell wall integrity, but also decreased sclerotia formation and virulence (Bashi et al, 2016; Cong et al, 2022). Likewise, deletion of the MAPKKK gene Ssos4 , a component of the high osmolarity MAPK pathway associated with mitigating hyperosmotic stressors, led to reduced sclerotia formation and virulence (Li et al, 2021).…”