Comparative genomics of color morphs in the coral Montastraea cavernosa (NitroFixCorals project)
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<p>Montastraea cavernosa is a common coral in the Caribbean basin found in several color morphs. To investigate the causes for brown and orange morphs we undertook a genomics approach on corals collected at the same time and depth in the Bahamas. The coral holobiont includes the host, symbiotic dinoflagellates (Symbiodinium spp.), and a diverse microbiome. While the coral host showed significant genetic differentiation between color morphs both the composition of the Symbiodinium spp. communities and the prokaryotic communities did not. Both targeted and global gene expression differences in the transcriptome of the host show no difference in fluorescent proteins while the metatranscriptome of the microbiome shows that pigments such as phycoerythrin and orange carotenoid protein of cyanobacterial origin are significantly greater in orange morphs, which is also consistent with the significantly greater number of cyanobacteria quantified by 16S rRNA reads and flow cytometry. The microbiome of orange color morphs expressed significantly more nitrogenase (nifH) transcripts consistent with their known ability to fix nitrogen. Both coral and Symbiodinium spp. transcriptomes from orange morphs had significantly increased expression of genes related to immune response and apoptosis, which may potentially be involved in maintaining and regulating the unique symbiont population in orange morphs.</p>
<p>穴状星孔珊瑚（Montastraea cavernosa）是加勒比海盆地常见珊瑚，存在多种色型。为探究棕色与橙色色型的形成机制，我们对在巴哈马海域同期、同深度采集的该种珊瑚开展了基因组学研究。该珊瑚的共生联合体（holobiont）包含宿主、共生甲藻（Symbiodinium spp.，虫黄藻属）以及多样的微生物组。尽管珊瑚宿主在不同色型间存在显著的遗传分化，但虫黄藻群落与原核生物群落的组成均未表现出此类差异。对宿主转录组的靶向基因表达与全局基因表达分析均显示，荧光蛋白的表达无显著差异；而微生物组的宏转录组分析则表明，橙色色型中源自蓝细菌的藻红蛋白与橙色胡萝卜素蛋白的表达量显著升高，这一结果与通过16S rRNA测序reads及流式细胞术定量得到的蓝细菌数量显著更多的结论相符。橙色色型的微生物组还显著高表达固氮酶（nitrogenase，nifH）转录本，这与其已知的固氮能力相一致。来自橙色色型的珊瑚宿主与虫黄藻的转录组中，与免疫应答及细胞凋亡相关的基因表达量均显著升高，这可能参与维持和调控橙色色型特有的共生菌群种群。</p>
