It has been known for quite some time that cytokinins, hormones typical of plants, are also produced and metabolized in bacteria. Most bacteria can only form the tRNA-bound cytokinins, but there are examples of plant-associated bacteria, both pathogenic and beneficial, that actively synthesize cytokinins to interact with their host. Similar to plants, bacteria produce diverse cytokinin metabolites, employing corresponding metabolic pathways. The identification of genes encoding the enzymes involved in cytokinin biosynthesis and metabolism facilitated their detailed characterization based on both classical enzyme assays and structural approaches. This review summarizes the present knowledge on key enzymes involved in cytokinin biosynthesis, modifications, and degradation in bacteria, and discusses their catalytic properties in relation to the presence of specific amino acid residues and protein structure.

• Klíčová slova
• CKX, LOG, cytochrome P450 monooxygenase, cytokinin, isopentenyl transferase, tRNA modification,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Cytokinins are plant hormones, derivatives of adenine with a side chain at the N6-position. They are involved in many physiological processes. While the metabolism of trans-zeatin and isopentenyladenine, which are considered to be highly active cytokinins, has been extensively studied, there are others with less obvious functions, such as cis-zeatin, dihydrozeatin, and aromatic cytokinins, which have been comparatively neglected. To help explain this duality, we present a novel hypothesis metaphorically comparing various cytokinin forms, enzymes of CK metabolism, and their signalling and transporter functions to the comics superheroes Hulk and Deadpool. Hulk is a powerful but short-lived creation, whilst Deadpool presents a more subtle and enduring force. With this dual framework in mind, this review compares different cytokinin metabolites, and their biosynthesis, translocation, and sensing to illustrate the different mechanisms behind the two CK strategies. This is put together and applied to a plant developmental scale and, beyond plants, to interactions with organisms of other kingdoms, to highlight where future study can benefit the understanding of plant fitness and productivity.

• Klíčová slova
• Hulk/Deadpool, aromatic cytokinins, cis-zeatin, cytokinin biosynthesis, cytokinin oxidase/dehydrogenase, cytokinin signalling, cytokinin transport, cytokinins, isopentenyl transferase,
• MeSH
• Arabidopsis metabolismus   MeSH
• biologické modely MeSH
• biologický transport MeSH
• biotest MeSH
• cytokininy metabolismus   MeSH
• fyziologie rostlin * MeSH
• glykosylace MeSH
• hydrolýza MeSH
• kinetika MeSH
• kinetin metabolismus   MeSH
• oxidoreduktasy metabolismus   MeSH
• regulátory růstu rostlin metabolismus   MeSH
• rostliny metabolismus   MeSH
• signální transdukce * MeSH
• vazba proteinů MeSH
• zeatin analogy a deriváty   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• cytokinin oxidase MeSH Prohlížeč
• cytokininy MeSH
• dihydrozeatin MeSH Prohlížeč
• kinetin MeSH
• oxidoreduktasy MeSH
• regulátory růstu rostlin MeSH
• zeatin MeSH

It has been recognized that cytokinins are plant hormones that influence not only numerous aspects of plant growth, development and physiology, including cell division, chloroplast differentiation and delay of senescence but the interaction with other organisms, including pathogens. Cytokinins are not only produced by plants but are also by other prokaryotic and eukaryotic organism such as bacteria, fungi, microalgae and insects. Notably, cytokinins are produced both by pathogenic and also beneficial microbes and are known to induce resistance in plants against pathogen infections. In this review the contrasting role of cytokinin for the defence and susceptibility of plants against bacterial and fungal pathogen and pest insects is assessed. We also discuss the cross talk of cytokinins with other phytohormones and the underlying mechanism involved in enhancing plant immunity against pathogen infections and explore possible practical applications in crop plant production.

• Klíčová slova
• beneficial microbe, host–pathogen interaction, insect, microalgae, phytohormones, plant growth promoting rhizobacteria,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

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.

• Klíčová slova
• Claviceps purpurea, Cytokinin, Cytokinin oxidase/dehydrogenase, Phosphoribohydrolase, Virulence,
• MeSH
• Claviceps patogenita   fyziologie   MeSH
• cytokininy metabolismus   MeSH
• interakce hostitele a patogenu fyziologie   MeSH
• nemoci rostlin mikrobiologie   MeSH
• žito * genetika   metabolismus   mikrobiologie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• cytokininy MeSH

It has long been known that hormones affect the interaction of a phytopathogen with its host plant. The pathogen can cause changes in plant hormone homeostasis directly by affecting biosynthesis or metabolism in the plant or by synthesizing and secreting the hormone itself. We previously demonstrated that pathogenic fungi of the Fusarium species complex are able to produce three major types of hormones: auxins, cytokinins, and gibberellins. In this work, we explore changes in the levels of these hormones in maize and mango plant tissues infected with Fusarium. The ability to produce individual phytohormones varies significantly across Fusarium species and such differences likely impact host specificity inducing the unique responses noted in planta during infection. For example, the production of gibberellins by F. fujikuroi leads to elongated rice stalks and the suppression of gibberellin biosynthesis in plant tissue. Although all Fusarium species are able to synthesize auxin, sometimes by multiple pathways, the ratio of its free form and conjugates in infected tissue is affected more than the total amount produced. The recently characterized unique pathway for cytokinin de novo synthesis in Fusarium appears silenced or non-functional in all studied species during plant infection. Despite this, a large increase in cytokinin levels was detected in F. mangiferae infected plants, caused likely by the up-regulation of plant genes responsible for their biosynthesis. Thus, the accumulation of active cytokinins may contribute to mango malformation of the reproductive organs upon infection of mango trees. Together, our findings provide insight into the complex role fungal and plant derived hormones play in the fungal-plant interactions.

• Klíčová slova
• Fusarium, auxin, cytokinin, gibberellin, host–pathogen interaction, mango malformation disease (MMD),
• Publikační typ
• časopisecké články MeSH

Among phytohormones, cytokinins (CKs) play an important role in controlling crucial aspects of plant development. Not only plants but also diverse microorganisms are able to produce phytohormones, including CKs, though knowledge concerning their biosynthesis and metabolism is still limited. In this work we demonstrate that the fungus Leptosphaeria maculans, a hemi-biotrophic pathogen of oilseed rape (Brassica napus), causing one of the most damaging diseases of this crop, is able to modify the CK profile in infected B. napus tissues, as well as produce a wide range of CKs in vitro, with the cis-zeatin derivatives predominating. The endogenous CK spectrum of L. maculans in vitro consists mainly of free CK bases, as opposed to plants, where other CK forms are mostly more abundant. Using functional genomics, enzymatic and feeding assays with CK bases supplied to culture media, we show that L. maculans contains a functional: (i) isopentenyltransferase (IPT) involved in cZ production; (ii) adenosine kinase (AK) involved in phosphorylation of CK ribosides to nucleotides; and (iii) CK-degradation enzyme cytokinin oxidase/dehydrogenase (CKX). Our data further indicate the presence of cis-trans isomerase, zeatin O-glucosyltransferase(s) and N6-(Δ2-isopentenyl)adenine hydroxylating enzyme. Besides, we report on a crucial role of LmAK for L. maculans fitness and virulence. Altogether, in this study we characterize in detail the CK metabolism of the filamentous fungi L. maculans and report its two novel components, the CKX and CK-related AK activities, according to our knowledge for the first time in the fungal kingdom. Based on these findings, we propose a model illustrating CK metabolism pathways in L. maculans.

• Klíčová slova
• Leptosphaeria maculans, adenosine kinase, cytokinin, cytokinin oxidase/dehydrogenase, isopentenyltransferase, zeatin cis/trans isomerase,
• Publikační typ
• časopisecké články MeSH

Species of the Fusarium fujikuroi species complex (FFC) cause a wide spectrum of often devastating diseases on diverse agricultural crops, including coffee, fig, mango, maize, rice, and sugarcane. Although species within the FFC are difficult to distinguish by morphology, and their genes often share 90% sequence similarity, they can differ in host plant specificity and life style. FFC species can also produce structurally diverse secondary metabolites (SMs), including the mycotoxins fumonisins, fusarins, fusaric acid, and beauvericin, and the phytohormones gibberellins, auxins, and cytokinins. The spectrum of SMs produced can differ among closely related species, suggesting that SMs might be determinants of host specificity. To date, genomes of only a limited number of FFC species have been sequenced. Here, we provide draft genome sequences of three more members of the FFC: a single isolate of F. mangiferae, the cause of mango malformation, and two isolates of F. proliferatum, one a pathogen of maize and the other an orchid endophyte. We compared these genomes to publicly available genome sequences of three other FFC species. The comparisons revealed species-specific and isolate-specific differences in the composition and expression (in vitro and in planta) of genes involved in SM production including those for phytohormome biosynthesis. Such differences have the potential to impact host specificity and, as in the case of F. proliferatum, the pathogenic versus endophytic life style.

• Klíčová slova
• Fusarium fujikuroi species complex, evolution, genome sequencing, in planta expression, metabolomics, secondary metabolism,
• MeSH
• fungální proteiny genetika   metabolismus   MeSH
• Fusarium genetika   izolace a purifikace   patogenita   MeSH
• genom fungální * MeSH
• hostitelská specificita genetika   MeSH
• kukuřice setá mikrobiologie   MeSH
• Mangifera mikrobiologie   MeSH
• metabolom MeSH
• molekulární evoluce MeSH
• Orchidaceae mikrobiologie   MeSH
• polymorfismus genetický * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fungální proteiny MeSH