Secondary metabolites in fungus-plant interactions

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Secondary metabolites in fungus-plant interactions

Fungi and plants are rich sources of thousands of secondary metabolites. The genetically coded possibilities for secondary metabolite production, the stimuli of the production, and the special phytotoxins basically determine the microscopic fungi-host plant interactions and the pathogenic lifestyle of fungi. The rewiew introduces plant secondary metabolites usually with antifungal effect as well as the importance of signaling molecules in induced systemic resistance and systemic acquired resistance processes. The review also concerns the mimicing of plant effector molecules like auxins, gibberellins and abscisic acid by fungal secondary metabolites that modulate plant growth or even can subvert the plant defense responses such as programmed cell death to gain nutrients for fungal growth and colonization. It also looks through the special secondary metabolite production and host selective toxins of some significant fungal pathogens and the plant response in form of phytoalexin production. New results coming from genome and transcriptional analyses in context of selected fungal pathogens and their hosts are also discussed

Complexation of desferricoprogen with trivalent Fe, Al, Ga, In and divalent Fe, Ni, Cu, Zn metal ions: effects of the linking chain structure on the metal binding ability of hydroxamate based siderophores

Complexes of the natural siderophore, desferricoprogen (DFC), with several trivalent and divalent metal ions in aqueous solution were studied by pH-potentiometry, UV–Vis spectrophotometry and cyclic voltammetry. DFC was found to be an effective metal binding ligand, which, in addition to Fe(III), forms complexes of high stability with Ga(III), Al(III), In(III), Cu(II), Ni(II) and Zn(II). Fe(II), however, is oxidized by DFC under anaerobic conditions and Fe(III) complexes are formed. By comparing the results with those of desferrioxamine B (DFB), it can be concluded that the conjugated b-double bond slightly increases the stability of the hydroxamate chelates, consequently increases the stability of mono-chelated complexes of DFC. Any steric effect by the connecting chains arises only in the bis- and tris-chelated complexes. With metal ions possessing a relatively big ionic radius (Cu(II), Ni(II), Zn(II), In(III)) DFC, containing a bit longer chains than DFB, forms slightly more stable complexes. With smaller metal ions the trend is the opposite. Also a notable difference is that stable trinuclear complex, [Cu3L2], is formed with DFC but not with DFB. Possible bio-relevance of the Fe(II)/Fe(III) results is also discussed in the paper

Degradation of glutathione in Aspergillus nidulans — Short communication

Relative transcriptions of Aspergillus nidulans dug1-3 (orthologes of Saccharomyces cerevisiae DUG — deficient in utilization of glutathione — pathway genes) and ggtA encoding γ-glutamyl transpeptidase were studied under conditions inducing glutathione degradation. GgtA was induced in all cases when glutathione levels decreased, but addition of yeast extract, which moderated glutathione degradation, enhanced its induction. Although dug2 showed constitutive transcription, dug1 and dug3 were induced by carbon and nitrogen starvation and yeast extract did not caused significant changes in their relative transcription. The in silico reconstructed DUG pathway of A. nidulans is a promising candidate for cytosolic GSH degradation induced by carbon/nitrogen stress

A protein foszfatáz Z szerepének felderítése a patogén gombák jelátviteli folyamataiban = Investigation of the function of protein phosphatase Z in the signal transduction of pathogenic fungi

A protein foszfatáz Z C. albicans ortológját kódoló gén, a CaPPZ1 klónozása és szekvenálása segítségével alátámasztottuk a humán patogén nagyfokú genetikai polimorfizmusát. Legalább 4 CaPPZ1 allélt azonosítottunk, és egy találtunk egy olyan hipervariábilis gén régiót, ami alkalmasnak bizonyult klinikai C. albicans izolátumok genotipizálása. In vitro mutagenézissel azonosítottuk a foszfatáz enzim aktivitását, illetve stabilitását biztosító aminosav oldalláncokat. Molekuláris genetikai módszerekkel bebizonyítottuk, hogy a CaPPZ1 szerepet játszik a gomba kation homeosztázisában, sejtfal bioszintézisében és membrán potenciáljának meghatározásában, valamint fontos a hifa növekedésben, és a patogén gomba fertőzőképességében. Megállapítottuk, hogy az A. fumigatus és az A. nidulans PPZ ortológok szerkezete konzerválódott, és a phzA, illetve a ppzA géntermékekről igazoltuk, hogy funkcionálisan helyettesítik a hiányzó PPZ enzimeket S. cerevisiae és S. pombe mutánsokban. Ennek ellenére a ppzA gén inaktiválása nem járt a várt fenotípusok változásokkal A. nidulansban, viszont érzékenységet okozott oxidálószer kezeléssel szemben. A genetikailag távol álló C. albicans és S. cerevisiae PPZ mutánsokkal történő összehasonlítás alapján arra a következtetésre jutottunk, hogy az PPZ enzimek részt vesznek a gombák oxidatív stressz válaszának modulálásában. Ily módon egy régóta ismert foszfatáz új funkcióját sikerült azonosítanunk. | By cloning and sequencing of the protein phosphatase Z (PPZ) coding CaPPZ1 gene we confirmed the high level of genetic polymorphism of the human pathogen C. albicans. We identified four different alleles of the gene and found a hypervariable DNA segment that was suitable for genotyping of clinical C. albicans isolates. With in vitro mutagenesis we pinpointed the amino acid residues that are important in the activity / stability of the phosphatase. With the aid of molecular genetics we revealed that CaPPZ1 was important in the cation homeostasis, cell wall integrity and membrane potential determination of the fungus. In addition to these general PPZ roles, we also found that CaPPZ1 was involved in the germ tube formation and in the virulence of the pathogen. By extending these results we predicted that the structures of the PPZ ortholog proteins were well conserved in A. fumigatus and A. nidulans, and demonstrated that the corresponding phzA and ppzA phosphatases behaved as the functional replacements of the yeast enzymes in S. cerevisiae and S. pombe deletion mutants. However, the inactivation of the PPZA gene did not result in the expected phenotypes in A. nidulans, but caused sensitivity to oxidative agents. By the comparison with the genetically distantly related C. albicans and S. cereveisiae PPZ mutants we proved that all of these PPZ phosphatases acted in the oxidative stress mediation of fungi. Thus, we identified a novel function for a long known enzyme family

General stress response or adaptation to rapid growth in Aspergillus nidulans?

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