Giant clams harbor three genera of symbiotic dinoflagellates (Symbiodinium, Cladocopium, and Durusdinium) as extracellular symbionts (zooxanthellae). While symbiotic dinoflagellates can synthesize amino acids to benefit the host, they are nitrogen‐deficient. Hence, the host must supply them with nitrogen including urea, which can be degraded to ammonia and carbon dioxide by urease (URE). Here, we report three complete coding cDNA sequences of URE, one for each genus of dinoflagellate, obtained from the colorful outer mantle of the giant clam, Tridacna squamosa. The outer mantle had higher transcript level of Tridacna squamosa zooxanthellae URE (TSZURE) than the whitish inner mantle, foot muscle, hepatopancreas, and ctenidium. TSZURE was immunolocalized strongly and atypically in the plastid, moderately in the cytoplasm, and weakly in the cell wall and plasma membrane of symbiotic dinoflagellates. In the outer mantle, illumination upregulated the protein abundance of TSZURE, which could enhance urea degradation in photosynthesizing dinoflagellates. The urea‐nitrogen released could then augment synthesis of amino acids to be shared with the host for its general needs. Illumination also enhanced gene and protein expression levels of TSZURE/TSZURE in the inner mantle and foot muscle, which contain only small quantities of symbiotic dinoflagellate, have no iridocyte, and lack direct exposure to light. With low phototrophic potential, dinoflagellates in the inner mantle and foot muscle might need to absorb carbohydrates in order to assimilate the urea‐nitrogen into amino acids. Amino acids donated by dinoflagellates to the inner mantle and the foot muscle could be used especially for synthesis of organic matrix needed for light‐enhanced shell formation and muscle protein, respectively.

中文翻译：

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共鞭毛科鞭毛虫在照明的三个亚细胞区室表达脲酶，并在大蛤three（Tridacna squamosa）的三个器官中原位上调其表达水平。

巨蛤怀有共生藻（的三个属共生，Cladocopium和Durusdinium）作为胞外共生体（虫黄藻）。虽然共生的鞭毛鞭毛藻酸酯可以合成氨基酸以使宿主受益，但它们是氮缺乏的。因此，宿主必须向他们提供包括尿素在内的氮，尿素可以被尿素酶（URE）降解为氨和二氧化碳。在这里，我们报告了URE的三个完整编码cDNA序列，每个双鞭毛藻属都有一个，从巨型蛤Tri Tridacna squamosa的彩色外层获得。地幔的Tridacna squamosa zooxanthellae URE（TSZURE）的转录水平较高），而不是发白的内部披风，脚部肌肉，肝胰腺和ctnedium。TSZURE在质体中非典型地强烈，非典型地免疫定位，在胞质中适度，而在共生鞭毛鞭毛的细胞壁和质膜中免疫弱化。在外地幔中，光照上调了TSZURE的蛋白质丰度，这可能会增强光合作用的鞭毛藻中尿素的降解。释放出的尿素氮可以增加氨基酸的合成，以供宿主满足其一般需要。照明还增强了TSZURE的基因和蛋白质表达水平内地幔和足部肌肉中的/ TSZURE仅包含少量共生的鞭毛鞭毛藻，没有虹膜细胞，并且缺乏直接暴露于光下的能力。由于光养势低，内地幔和足部肌肉中的鞭毛虫可能需要吸收碳水化合物才能将尿素氮吸收为氨基酸。鞭毛鞭毛虫捐赠给内套和足部肌肉的氨基酸可特别用于分别用于增强壳形成和肌肉蛋白质的有机基质的合成。