Pathogen-derived cytokinins (CKs) have been recognized as important virulence factor in several host-pathogen interactions and it was demonstrated multiple times that phytopathogenic fungi form CKs via the tRNA degradation pathway. In contrast to previous studies, the focus of this study is on the second step of CK formation and CK degradation to improve our understanding of the biosynthesis in fungi on the one hand, and to understand CK contribution to the infection process of Claviceps purpurea on the other hand. The ergot fungus Claviceps purpurea is a biotrophic phytopathogen with a broad host range including economically important crops causing harvest intoxication upon infection. Its infection process is restricted to unfertilized ovaries without causing macroscopic defense symptoms. Thus, sophisticated host manipulation strategies are implicated. The cytokinin (CK) plant hormones are known to regulate diverse plant cell processes, and several plant pathogens alter CK levels during infection. C. purpurea synthesizes CKs via two mechanisms, and fungus-derived CKs influence the host-pathogen interaction but not fungus itself. CK deficiency in fungi with impact on virulence has only been achieved to date by deletion of a tRNA-ipt gene that is also involved in a process of translation regulation. To obtain a better understanding of CK biosynthesis and CKs' contribution to the plant-fungus interaction, we applied multiple approaches to generate strains with altered or depleted CK content. The first approach is based on deletion of the two CK phosphoribohydrolase (LOG)-encoding genes, which are believed to be essential for the release of active CKs. Single and double deletion strains were able to produce all types of CKs. Apparently, log gene products are dispensable for the formation of CKs and so alternative activation pathways must be present. The CK biosynthesis pathway remains unaffected in the second approach, because it is based on heterologous overexpression of CK-degrading enzymes from maize (ZmCKX1). Zmckx1 overexpressing C. purpurea strains shows strong CKX activity and drastically reduced CK levels. The strains are impaired in virulence, which reinforces the assumption that fungal-derived CKs are crucial for full virulence. Taken together, this study comprises the first analysis of a log depletion mutant that proved the presence of alternative cytokinin activation pathways in fungi and showed that heterologous CKX expression is a suitable approach for CK level reduction.
- MeSH
- Claviceps * fyziologie klasifikace patogenita MeSH
- ergotismus etiologie patologie MeSH
- lidé MeSH
- námelové alkaloidy chemie škodlivé účinky terapeutické užití MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- práce podpořená grantem MeSH
Claviceps purpurea is an ovarian parasite infecting grasses (Poaceae) including cereals and forage plants. This fungus produces toxic alkaloids and consumption of contaminated grains can cause ergotism in humans and other mammals. Recent molecular genetics studies have indicated that it included three cryptic species (G1, G2, G3). In this study, reproductive isolation amongst these groups and among material from Phragmites and Molinia was tested using gene flow statistics for five polymorphic loci, and to support these data, phylogenetic affiliations based on gene trees and a multigene phylogeny were used. The four recognized species are characterized based on morphology and host spectrum and formal taxonomic names are proposed. Claviceps purpurea sensu stricto (G1 group) represents a typical rye ergot, but infects various other grasses. Typical hosts of Claviceps humidiphila (new name for G2 species), like Phalaris arundinacea, belong to grasses preferring humid locations. Claviceps spartinae (G3) is specific to chloridoid grasses from salt barches. The material from Phragmites and Molinia can be authenticated with the species Claviceps microcephala for which the new name Claviceps arundinis is proposed here. The divergence time between species was estimated and the tools for species identification are discussed.
- MeSH
- Claviceps klasifikace genetika izolace a purifikace fyziologie MeSH
- DNA fungální chemie genetika MeSH
- fylogeneze MeSH
- hostitelská specificita MeSH
- lipnicovité mikrobiologie MeSH
- molekulární sekvence - údaje MeSH
- sekvenční analýza DNA MeSH
- sekvenční homologie MeSH
- shluková analýza MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- MeSH
- alkaloidy biosyntéza MeSH
- Claviceps fyziologie MeSH
- kultivované buňky sekrece MeSH
- lidé MeSH
- Check Tag
- lidé MeSH
- MeSH
- alkaloidy biosyntéza MeSH
- buněčné kultury MeSH
- Claviceps fyziologie MeSH
- lidé MeSH
- škrob fyziologie MeSH
- Check Tag
- lidé MeSH
- MeSH
- alkaloidy biosyntéza MeSH
- Claviceps fyziologie MeSH
- kultivované buňky sekrece MeSH
- lidé MeSH
- Check Tag
- lidé MeSH
