Identification of zooxanthellate genes that are involved in symbiosis with a reef coral, and analyses of their function and expression

独生型(或造礁)珊瑚与共生的甲藻共生共生。(通常称为虫黄藻)。为了鉴定和鉴定在共生状态下比在栖息地外条件下表达水平更高的共生细菌mRNAs，试图建立一个模式共生系统，该系统由珊瑚Acropora tenuis的新变质的息肉和虫黄藻的单克隆种群组成。为此，对几个培养的共生线虫细胞系进行了对细嫩艾美耳球虫自然非共生息肉的感染性测试。两株A分支菌株(PL-TS-1和CCMP2467)高密度侵染幼虫，促进寄主生长。为了鉴定参与建立或维持共生关系的PL-TS-1(或A.tenuis)基因，进行了抑制消减杂交。大约对消减文库中的50个克隆进行了分析，但共生诱导的PL-TS-1的mRNAs在所分析的cDNA群中不存在。然而，可以确定两个mRNAs，它们的表达水平因共生体的存在而增加了两倍以上。这两个mRNAs命名为AtSym-01和-02，分别编码具有一个跨膜结构域的Syndecan家族蛋白和SLC26A11家族的安娜不依赖的硫酸盐转运蛋白(这是首次在此类珊瑚mRNAs中发现的)。分析了PL-TS-1中两个肌动蛋白基因(SyAct-A1和-A2)在体内和体外条件下的表达水平，结果强烈表明，与珊瑚共生时SyAct-A2 mRNA的表达高于体外培养。

Hermatypic (or reef-building) corals live in obligate mutualistic symbiosis with the symbiotic dinoflagellates Symbiodinium spp. (generally known as zooxanthellae). With the purpose of identifying and characterizing Symbiodinium mRNAs whose expression levels are enhanced in the symbiotic state than in ex hospite conditions, attempts were made to establish a model symbiosis system consisting of newly metamorphosed polyps of the reef coral Acropora tenuis and a monoclonal population of zooxanthellae. To this end, infectivity of several cultured Symbiodinium cell lines was tested on naturally aposymbiotic polyps of A. tenuis. Two clade A strains (PL-TS-1 and CCMP2467) infected the juveniles at high densities, and promoted growth of the host. To identify PL-TS-1 (or A. tenuis) genes involved in the establishment or maintenance of symbiosis, suppression subtractive hybridization was performed. Approx. 50 cDNA clones in the subtracted library were analyzed, but symbiotically induced mRNAs of PL-TS-1 were not represented in the analyzed cDNA population. However, two mRNAs, the expression levels of which were augmented more than twofold by the presence of the symbionts, could be identified. The mRNAs, named AtSym-01 and -02, encode a syndecan family protein with one trans-membrane domain, and an Na^+-independent sulfate transporter of the SLC26A11 family, respectively (it was the first identification on such coral mRNAs). Two actin mRNAs (SyAct-A1 and -A2) in PL-TS-1 were analyzed for the expression levels in the in and ex hospite conditions, and the result strongly suggested that the expression of the SyAct-A2 mRNA was higher in symbiosis with the coral than in in vitro culture.