RESUMO
The ascomycete Candida albicans is the most common fungal pathogen in immunocompromised patients . Its ability to change morphology, from yeast to filamentous forms, in response to host environmental cues is important for virulence . Filamentation is mediated by second messengers such as cyclic adenosine 3',5'-monophosphate (cAMP) synthesized by adenylyl cyclase . The distantly related basidiomycete Cryptococcus neoformans is an encapsulated yeast that predominantly infects the central nervous system in immunocompromised patients . Similar to the morphological change in C. albicans, capsule biosynthesis in C. neoformans, a major virulence attribute, is also dependent upon adenylyl cyclase activity . Here we demonstrate that physiological concentrations of CO2/HCO3- induce filamentation in C. albicans by direct stimulation of cyclase activity. Furthermore, we show that CO2/HCO3- equilibration by carbonic anhydrase is essential for pathogenesis of C. albicans in niches where the available CO2 is limited. We also demonstrate that adenylyl cyclase from C. neoformans is sensitive to physiological concentrations of CO2/HCO3-. These data demonstrate that the link between cAMP signaling and CO2/HCO3- sensing is conserved in fungi and reveal CO2 sensing to be an important mediator of fungal pathogenesis. Novel therapeutic agents could target this pathway at several levels to control fungal infections.
Assuntos
Adenilil Ciclases/metabolismo , Candida albicans/enzimologia , Candida albicans/patogenicidade , Dióxido de Carbono/metabolismo , Cryptococcus neoformans/enzimologia , AMP Cíclico/metabolismo , Transdução de Sinais/fisiologia , Animais , Bicarbonatos/metabolismo , Candida albicans/genética , Candida albicans/crescimento & desenvolvimento , Candidíase/mortalidade , Anidrases Carbônicas/metabolismo , Cryptococcus neoformans/metabolismo , Indução Enzimática/fisiologia , Feminino , Teste de Complementação Genética , Camundongos , Camundongos Endogâmicos BALB C , Análise de Sobrevida , VirulênciaRESUMO
Agrobacterium tumefaciens was used to transform Ascochyta rabiei, the causal agent of chickpea blight. Employing a T-DNA containing a hygromycin resistance gene (hph), 908 transformants were obtained from germinated pycnidiospores on a selective medium containing hygromycin. Transformants were confirmed using PCR and Southern analyses and of four of these that were tested, two had integrated multicopies of the hph gene, one had two copies and one had a single insertion. Transformants were tested for the production of solanapyrone A toxin using a microtitre plate assay. Loss of toxin production by transformants was confirmed by reversed phase high-performance liquid chromatography. Sixteen transformants out of 668 tested produced significantly less solanapyrone A than the wild-type strain.