Identification of genes involved in symbiosis of green hydra and Chlorella. Hydra viridissima

Green hydra (Hydra viridissima) harbors endosymbiotic Chlorella and have established a mutual relation. To identify the host hydra genes involved in the specific symbiotic relationship, transcriptomes of intact H. viridissima colonized with symbiotic Chlorella strain A99, aposymbiotic H.viridissima and H. viridissima artificially infected with other symbiotic Chlorella were compared by microarray analysis. The results indicated that genes involved in nutrition supply to Chlorella were upregulated in the symbiotic hydra. In addition, it was induced by supply of photosynthates from the symbiont to the host, suggesting cooperative metabolic interaction between the host and the symbiotic algae. Overall design: For the microarray analysis, we used intact H.viridissima A99 in asexual phase, that in sexual phase, aposymbiotic H.viridissima A99 which removed symbiotic algae, and H.viridissima A99 which removed the symbiotic algae and artificially infected Chlorella variabilis NC64A known as the symbiotic Chlorella of paramecium. The experiments using three biological replicates for each sample were performed using the total RNA from whole polyps after light exposure for six hour.

绿色水螅（Hydra viridissima）体内携带有内共生小球藻属（Chlorella），并与之建立了互利共生关系。为鉴定参与该特异性共生关系的宿主水螅基因，研究人员通过微阵列（microarray）分析，对比了三类样本的转录组（transcriptome）：定植有共生小球藻菌株A99的完整绿色水螅、无共生体的绿色水螅，以及人工感染其他共生小球藻的绿色水螅。
分析结果显示，为小球藻属提供营养的基因在共生水螅中表达上调。此外，该基因的上调可由共生体向宿主传递的光合产物（photosynthates）所诱导，表明宿主与共生藻类之间存在协同代谢互作。
总体实验设计：本微阵列分析所用样本包括：无性繁殖期的完整绿色水螅A99、有性繁殖期的完整绿色水螅A99、去除共生藻的无共生体绿色水螅A99，以及去除原生共生藻后，人工感染已知为草履虫共生小球藻的小球藻（Chlorella variabilis）NC64A的绿色水螅A99。所有样本均在光照6小时后，从完整水螅体中提取总RNA，每个样本设置3次生物学重复（biological replicates）。