Sea cucumber Apostichopus japonicus is an important economic species in echinoderms; however, its culture frequently suffered from diseases. Environmental stress was found to be a dominant inducer of A. japonicus diseases, and thus, discovering the characteristics of immune system under environmental stress is of great significance for disease control in A. japonicus culture. Phenoloxidase (PO) is recognized as a crucial immune‐related enzyme in invertebrates. In order to preliminarily illustrate the different roles that A. japonicus PO isoforms play under environmental stresses, the transcriptional expression of three identified A. japonicus PO isoforms (named as AjPOI, AjPOII and AjPOIII respectively) after different in vivo environmental stress simulations was determined with quantitative real‐time PCR method. Meanwhile, the transcriptional expression analysis of other representational immune‐related factors under environmental stresses was also performed for the evaluation of relationships between AjPOs and other immune‐related factors. The correlations between AjPOs and other immune‐related factors were analysed using Pearson correlation coefficient, and the effects of AjPOs on other immune‐related factors were then tested by dsRNA interference method. The results of transcriptional expression analysis indicated that AjPOI was involved in the resistance to low salinity, low temperature and hypoxia; AjPOII and AjPOIII were both required for the resistance to low salinity, high temperature, low temperature and hypoxia; and all three AjPOs were excluded from the response against high salinity. In addition, three AjPOs were found to take part in different periods of resistance to environmental stresses, and this property made A. japonicus PO system capable of outputting resistance activities continuously. The correlation analysis combined with dsRNA interference test revealed that AjPOI was capable of regulating AjCTSD, AjI‐LYZ and AjMTF expression; AjPOII and AjPOIII both played important roles in the regulation of AjC‐LYZ expression; and AjPOIII was also able to regulate AjToll expression. These findings suggested that A. japonicus PO isoforms function in innate immunity not only via catalysing the oxidative reactions, but also by broadly regulating the expression of other immune‐related factors. On the whole, three AjPOs showed obvious differences among each other in the resistance to environmental stresses and the regulation of other immune‐related factors, but comparatively, AjPOII and AjPOIII shared more similarity.

中文翻译：

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环境胁迫下酚氧化酶在海参中的作用

海参刺参是棘皮动物中的一种重要经济物种。但是，它的文化经常遭受疾病的折磨。发现环境胁迫是日本根瘤菌疾病的主要诱因，因此，发现环境胁迫下的免疫系统特征对于日本根瘤菌培养中的疾病控制具有重要意义。酚氧化酶（PO）被认为是无脊椎动物中至关重要的免疫相关酶。为了初步说明在环境胁迫下日本刺参PO异构体发挥的不同作用，鉴定了三种日本刺参的转录表达使用定量实时PCR方法确定不同的体内环境胁迫模拟后的PO同工型（分别命名为AjPOI，AjPOII和AjPOIII）。同时，还进行了环境胁迫下其他代表性免疫相关因子的转录表达分析，以评估AjPOs与其他免疫相关因子之间的关系。使用Pearson相关系数分析AjPO与其他免疫相关因子之间的相关性，然后通过dsRNA干扰法测试AjPO对其他免疫相关因子的影响。转录表达分析结果表明，AjPOI参与了对低盐度，低温和低氧的抗性。AjPOII和AjPOIII都需要抗低盐度，高温，低温和缺氧；并且将所有三个AjPO排除在针对高盐度的响应之外。此外，发现三个AjPOs参与了不同的抗环境压力时期，这一特性使得能够连续输出抗性活动的日本粳稻PO系统。相关分析和dsRNA干扰试验结果表明，AjPOI具有调节AjCTSD，AjI-LYZ和AjMTF表达的能力。AjPOII和AjPOIII在AjC-LYZ表达的调节中都起着重要作用。并且AjPOIII也能够调节AjToll的表达。这些发现表明，日本刺参PO同工型不仅通过催化氧化反应，还通过广泛调节其他与免疫相关的因子的表达而发挥先天免疫的功能。总体而言，三种AjPO在抗环境压力和调节其他免疫相关因子方面表现出明显的差异，但相比之下，AjPOII和AjPOIII具有更大的相似性。