Functional characterization of the three mitogen‐activated protein kinase kinases (MAP2Ks) present in the Cryphonectria parasitica genome reveals the necessity of Cpkk1 and Cpkk2, but not Cpkk3, for pathogenesis on chestnut (Castanea spp.)

Abstract

The biological function(s) of the cpkk1, cpkk2 and cpkk3 genes, encoding the three mitogen-activated protein kinase kinases (MAP2Ks) of Cryphonectria parasitica, the causal agent of chestnut blight, were examined through knockout strains. Cpkk1, the Mkk1 orthologue, acts in a phosphorylation cascade essential for cell integrity; Cpkk2 is the Ste7 orthologue involved in the pheromone response pathway; Cpkk3 is the Pbs2 orthologue, the MAP2K activated during the high-osmolarity response. Our analysis confirmed the role of each MAP2K in its respective signalling cascade with some peculiarities: abnormal hyphae with a reduced number of septa and thinner cell walls were observed in Δcpkk1 mutants, and a strong growth defect on solid media was evident in Δcpkk2 mutants, when compared with the controls. Virulence on chestnut was affected in both the Δcpkk1 and Δcpkk2 strains, which were also unable to complete the developmental steps essential for mating. No alterations were reported in Δcpkk3, except under hyperosmotic conditions and in the presence of fludioxonil. Δcpkk2 mutants, however, showed higher sensitivity during growth in medium containing the antibiotic G418 (Geneticin).

Time‐resolved dissection of the molecular crosstalk driving Fusarium head blight in wheat provides new insights into host susceptibility determinism

“…This is an interesting finding because Fg is supposed to colonize cereal grains (Leonard & Bushnell, 2003) where photosynthesis is not expected. A systemic spreading in the vascular system has already been observed for DON and for fungal effectors (Lievens, Houterman, & Rep, 2009;Moretti, Rossi, Ciuffo, & Turina, 2014). Likewise, Fg effector proteins could also be delivered in the xylem to reach particular targets in photosynthetic tissues, thus interrogating the ability of Fg to remotely control specific processes in leaves and stems.…”

Mutation of the Slt2 ortholog from Cryphonectria parasitica results in abnormal cell wall integrity and sectorization with impaired pathogenicity

“…Thus, the CWI pathway is known to be significant determinant of differentiation and pathogenesis. In C. parasitica , cpkk1 , an ortholog of yeast Mkk1 in the CWI pathway, has been implicated in hypoviral regulation and fungal virulence 18 , 25 , 27 . Interestingly, recent studies of CpBck1 , an ortholog of yeast Bck1 in the CWI pathway, showed that CpBck1 -null mutants had phenotypic changes similar to those observed in Bck1 -null mutants of other fungi and also unique changes such as ultrastructural alterations and sporadic sectorization 26 , 37 .…”

“…In C. parasitica , several genes in MAPK pathways and their downstream effectors are regulated by hypovirus, or are involved in pathogenicity 9 , 16 , 17 , 23 – 26 . Among these pathways, the CWI pathway has aroused interest because Cpkk1 , an ortholog of yeast Mkk2 (a CWI MAPKK) was found to be modulated by hypovirus and was important for virulence in the chestnut tree 25 , 27 . In addition, recent studies on a mutant of CpBck1 , an ortholog of yeast Bck1 (a CWI MAPKKK), showed characteristic phenotypic changes related to CWI and virulence 26 .…”

Transmission of Penicillium aurantiogriseum partiti‐like virus 1 to a new fungal host (Cryphonectria parasitica) confers higher resistance to salinity and reveals adaptive genomic changes

“…We first assessed a possible effect of PaPLV1 on C. parasitica virulence on chestnut cuttings after forced vegetation during dormancy exactly as previously described (Moretti et al, 2014).…”