The role of mitogen‐activated protein (MAP) kinase signalling components and the Ste12 transcription factor in germination and pathogenicity of Botrytis cinerea

Abstract

SUMMARYIn all fungi studied so far, mitogen-activated protein (MAP) kinase cascades serve as central signalling complexes that are involved in vari~us aspects of growth, stress response and infection, In this work, putative components of the yeast Fus3/Kss1-type MAP kinase cascade and the putative downstream transcription factor Ste12 were analysed in the grey mould fungus Botrytis cinerea. Deletion mutants of the MAP triple kinase Ste11, the MAP kinase kinase Ste7 and the MAP kinase adaptor protein Ste50 all resulted in phenotypes similar to that of the previously described BMP1 MAP kinase mutant, namely defects in germination, delayed vegetative growth, reduced size of conidia, lack of sclerotia formation and loss of path9genicity. Mutants lacking Ste12 showed normal germination, but delayed infection as a result of low penetration efficiency. Two differently spliced ste12 transcripts were detected, and both were able to complement the ste12 mutant, except for a defect in sclerotium formation, which was only corrected by the full-sized transcript.Overexpression of the smaller ste12 transcript resulted in delayed germination and strongly reduced infection. Bc-Gas2, a homologue of Magnaporthe grisea Gas2 that is required for appressorial function, was found to be non-essential for growth and infection, but its expression was under the control of both Bmp1 and Ste12. In summary, the role and regulatory connections of the Fus3/Kss1-type MAP kinase cascade in B. cinerea revealed both common and unique properties compared with those of other plant pathogenic fungi, and provide evidence for a regulatory link between the BMP1 MAP kinase cascade and Ste12.

Transcriptome Profiling of Botrytis cinerea Conidial Germination Reveals Upregulation of Infection-Related Genes during the Prepenetration Stage

“…In addition, germ tubes continue to elongate on hydrophobic surfaces and never differentiate appressoria, indicating that they are defective in signaling leading to appressorium formation (Fig. 2B) (27,30). By comparing gene expression in wild-type and bmp1 mutant germlings, we aimed to identify genes that are involved in the appressorium differentiation process.…”

“…In addition to their role in germination, the cAMP and the BMP1 MAPK signaling pathways are required for appressorium differentiation, penetration, and host colonization, similar to the situation in other plant-pathogenic fungi (31,32). The MAPK cascade ste11, ste7, bmp1, and ste50 mutants did not form appressoria on hard surfaces, they failed to penetrate into host tissue, and they were nonpathogenic (27,30). Other signaling elements found to be involved in germination are the small GTPase Cdc42 and phospholipase C (Plc1) (33).…”

“…For normal carbon sourceinduced germination on hard surfaces, an intact cAMP signaling pathway, which includes Ras2, the G␣3 subunit of the heterotrimeric G protein, and adenylate cyclase, is required (27,29). In contrast, hydrophobic-surface-induced germination is dependent on a functional mitogen-activated protein kinase (MAPK) cascade (Ste11-Ste7-BMP1) (27,30). B. cinerea mutants lacking either of the three MAPK components, or the putative adaptor protein Ste50, did not germinate on hydrophobic surfaces in pure water (30).…”

“…In contrast, hydrophobic-surface-induced germination is dependent on a functional mitogen-activated protein kinase (MAPK) cascade (Ste11-Ste7-BMP1) (27,30). B. cinerea mutants lacking either of the three MAPK components, or the putative adaptor protein Ste50, did not germinate on hydrophobic surfaces in pure water (30). After germination, the germ tube elongates on the host surface to different lengths before tip growth stops and penetration is initiated.…”

When green and red mycology meet: Impressions from an interdisciplinary forum on virulence mechanisms of phyto- and human-pathogenic fungi

“…26 The contribution of alveolar epithelial cells in fungicidal defense was demonstrated by in vitro studies as well as in murine infections, thereby affecting the immunotolerant disposal of inhaled A. fumigatus conidia. Matthias Hahn from the University of Kaiserslautern, Germany, next gave an overview about the spread and fitness of multi-resistant strains of the necrotrophic plant pathogen Botrytis cinerea 27 and described a role of a sensor protein, Sho1, related to BMP1 MAPK signaling 28,29 in pH modulation. Interestingly, sho1 mutants phenocopy the lack of velvet complex components such as Vel1 or Lae1; 30 however, transcriptional profiling studies in planta revealed similarities but also significant differences, leaving the connection between Sho1 and the velvet complex an open issue.…”