RESUMO
Giant clams (genus Tridacna) are iconic coral reef animals of the Indian and Pacific Oceans, easily recognizable by their massive shells and vibrantly colored mantle tissue. Most Tridacna species are listed by CITES and the IUCN Redlist, as their populations have been extensively harvested and depleted in many regions. Here, we survey Tridacna crocea and Tridacna maxima from the eastern Indian and western Pacific Oceans for mitochondrial (COI and 16S) and nuclear (ITS) sequence variation and consolidate these data with previous published results using phylogenetic analyses. We find deep intraspecific differentiation within both T. crocea and T. maxima. In T. crocea we describe a previously undocumented phylogeographic division to the east of Cenderawasih Bay (northwest New Guinea), whereas for T. maxima the previously described, distinctive lineage of Cenderawasih Bay can be seen to also typify western Pacific populations. Furthermore, we find an undescribed, monophyletic group that is evolutionarily distinct from named Tridacna species at both mitochondrial and nuclear loci. This cryptic taxon is geographically widespread with a range extent that minimally includes much of the central Indo-Pacific region. Our results reinforce the emerging paradigm that cryptic species are common among marine invertebrates, even for conspicuous and culturally significant taxa. Additionally, our results add to identified locations of genetic differentiation across the central Indo-Pacific and highlight how phylogeographic patterns may differ even between closely related and co-distributed species.
Assuntos
Cardiidae/genética , Filogeografia , Animais , Teorema de Bayes , DNA Mitocondrial/genética , Complexo IV da Cadeia de Transporte de Elétrons/genética , Oceano Índico , Dados de Sequência Molecular , Oceano Pacífico , Especificidade da EspécieRESUMO
Ionotropic glutamate receptors (iGluRs) are ligand-gated cation channels that mediate neurotransmission in animal nervous systems. Homologous proteins in plants have been implicated in root development, ion transport, and several metabolic and signaling pathways. AtGLR3.4, a plant iGluR homolog from Arabidopsis thaliana, has ion channel activity and is gated by asparagine, serine, and glycine. Using heterologous expression in Xenopus oocytes, we found that another Arabidopsis iGluR homolog, AtGLR1.4, functioned as a ligand-gated, nonselective, Ca(2+)-permeable cation channel that responded to an even broader range of amino acids, none of which are agonists of animal iGluRs. Seven of the 20 standard amino acids--mainly hydrophobic ones--acted as agonists, with methionine being most effective and most potent. Nine amino acids were antagonists, and four, including glutamate and glycine, had no effect on channel activity. We constructed a model of this previously uncharacterized ligand specificity and used knockout mutants to show that AtGLR1.4 accounts for methionine-induced membrane depolarization in Arabidopsis leaves.
Assuntos
Aminoácidos/metabolismo , Proteínas de Arabidopsis/metabolismo , Canais de Cálcio/metabolismo , Ativação do Canal Iônico/fisiologia , Canais Iônicos/metabolismo , Sequência de Aminoácidos , Aminoácidos/química , Aminoácidos/farmacologia , Animais , Proteínas de Arabidopsis/classificação , Proteínas de Arabidopsis/genética , Canais de Cálcio/classificação , Canais de Cálcio/genética , Agonistas de Aminoácidos Excitatórios/química , Agonistas de Aminoácidos Excitatórios/metabolismo , Agonistas de Aminoácidos Excitatórios/farmacologia , Antagonistas de Aminoácidos Excitatórios/química , Antagonistas de Aminoácidos Excitatórios/metabolismo , Antagonistas de Aminoácidos Excitatórios/farmacologia , Feminino , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Células HEK293 , Humanos , Interações Hidrofóbicas e Hidrofílicas , Ativação do Canal Iônico/efeitos dos fármacos , Ativação do Canal Iônico/genética , Canais Iônicos/classificação , Canais Iônicos/genética , Potenciais da Membrana/efeitos dos fármacos , Metionina/química , Metionina/metabolismo , Metionina/farmacologia , Microscopia Confocal , Dados de Sequência Molecular , Mutação , Oócitos/metabolismo , Oócitos/fisiologia , Filogenia , Receptores de Glutamato/genética , Receptores de Glutamato/metabolismo , Homologia de Sequência de Aminoácidos , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genética , Transdução de Sinais/fisiologia , Xenopus laevisRESUMO
The family of ionotropic glutamate receptors includes 2 subunits, delta1 and delta2, the physiological relevance of which remains poorly understood. Both are nonfunctional in heterologous expression systems, although the isolated, crystallized ligand binding domain (LBD) of delta2 is capable of binding D-serine. To investigate these seemingly contradictory observations we tested whether delta receptors can be ligand gated at all. We used a strategy that replaced the native LBD of delta2 by a proven glutamate-binding LBD. Test transplantations between alpha-amino-3-hydroxy-5-methylisoxazole propionate (AMPA) and kainate receptors (GluR1 and GluR6, respectively) showed that this approach can produce functional chimeras even if only one part of the bipartite LBD is swapped. Upon outfitting delta2 with the LBD of GluR6, the chimera formed glutamate-gated ion channels with low Ca(2+) permeability and unique rectification properties. Ligand-induced conformational changes can thus gate delta2, suggesting that the LBD of this receptor works fundamentally differently from that of other ionotropic glutamate receptors.
