Identification of genes involved in symbiosis of green hydra and Chlorella

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. 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.