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1.
Eukaryot Cell ; 14(9): 958-63, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-26150416

RESUMO

Phototaxis in flagellated zoospores of the aquatic fungus Blastocladiella emersonii depends on a novel photosensor, Blastocladiella emersonii GC1 (BeGC1), comprising a type I (microbial) rhodopsin fused to a guanylyl cyclase catalytic domain, that produces the conserved second messenger cyclic GMP (cGMP). The rapid and transient increase in cGMP levels during the exposure of zoospores to green light was shown to be necessary for phototaxis and dependent on both rhodopsin function and guanylyl cyclase activity. It is noteworthy that BeGC1 was localized to the zoospore eyespot apparatus, in agreement with its role in the phototactic response. A putative cyclic nucleotide-gated channel (BeCNG1) was also identified in the genome of the fungus and was implicated in flagellar beating via the action of a specific inhibitor (l-cis-diltiazem) that compromised zoospore motility. Here we show that B. emersonii expresses a K(+) channel that is activated by cGMP. The use of specific channel inhibitors confirmed the activation of the channel by cGMP and its K(+) selectivity. These characteristics are consistent with the function of an ion channel encoded by the BeCNG1 gene. Other blastocladiomycete fungi, such as Allomyces macrogynus and Catenaria anguillulae, possess genes encoding a similar K(+) channel and the rhodopsin-guanylyl cyclase fusion protein, while the genes encoding both these proteins are absent in nonflagellated fungi. The presence of these genes as a pair seems to be an exclusive feature of blastocladiomycete fungi. Taken together, these data demonstrate that the B. emersonii cGMP-activated K(+) channel is involved in the control of zoospore motility, most probably participating in the cGMP-signaling pathway for the phototactic response of the fungus.


Assuntos
Blastocladiomycota/metabolismo , Canais de Cátion Regulados por Nucleotídeos Cíclicos/metabolismo , Proteínas Fúngicas/metabolismo , Canais de Potássio/metabolismo , Blastocladiomycota/genética , Blastocladiomycota/fisiologia , GMP Cíclico/metabolismo , Canais de Cátion Regulados por Nucleotídeos Cíclicos/genética , Proteínas Fúngicas/genética , Potenciais da Membrana , Potássio/metabolismo , Canais de Potássio/genética , Esporos Fúngicos/metabolismo
2.
Curr Biol ; 24(11): 1234-40, 2014 Jun 02.
Artigo em Inglês | MEDLINE | ID: mdl-24835457

RESUMO

Sensing light is the fundamental property of visual systems, with vision in animals being based almost exclusively on opsin photopigments [1]. Rhodopsin also acts as a photoreceptor linked to phototaxis in green algae [2, 3] and has been implicated by chemical means as a light sensor in the flagellated swimming zoospores of the fungus Allomyces reticulatus [4]; however, the signaling mechanism in these fungi remains unknown. Here we use a combination of genome sequencing and molecular inhibition experiments with light-sensing phenotype studies to examine the signaling pathway involved in visual perception in the closely related fungus Blastocladiella emersonii. Our data show that in these fungi, light perception is accomplished by the function of a novel gene fusion (BeGC1) of a type I (microbial) rhodopsin domain and guanylyl cyclase catalytic domain. Photobleaching of rhodopsin function prevents accumulation of cGMP levels and phototaxis of fungal zoospores exposed to green light, whereas inhibition of guanylyl cyclase activity negatively affects fungal phototaxis. Immunofluorescence microscopy localizes the BeGC1 protein to the external surface of the zoospore eyespot positioned close to the base of the swimming flagellum [4, 5], demonstrating this is a photoreceptive organelle composed of lipid droplets. Taken together, these data indicate that Blastocladiomycota fungi have a cGMP signaling pathway involved in phototaxis similar to the vertebrate vision-signaling cascade but composed of protein domain components arranged as a novel gene fusion architecture and of distant evolutionary ancestry to type II rhodopsins of animals.


Assuntos
Blastocladiella/fisiologia , Proteínas Fúngicas/genética , Guanilato Ciclase/genética , Luz , Rodopsina/genética , Transdução de Sinais , Sequência de Aminoácidos , Sequência de Bases , Blastocladiella/genética , Clonagem Molecular , DNA Complementar/genética , DNA Complementar/metabolismo , Proteínas Fúngicas/metabolismo , Fusão Gênica , Guanilato Ciclase/metabolismo , Dados de Sequência Molecular , Filogenia , Estrutura Terciária de Proteína , Rodopsina/metabolismo , Alinhamento de Sequência , Percepção Visual
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