IDENTIFICATION OF THE HIGH-TEMPERATURE RESPONSE GENES FROM PORPHYRA SERIATA (RHODOPHYTA) EXPRESSION SEQUENCE TAGS AND ENHANCEMENT OF HEAT TOLERANCE OF CHLAMYDOMONAS (CHLOROPHYTA) BY EXPRESSION OF THE PORPHYRA HTR2 GENE

Temperature is one of the major environmental factors that affect the distribution, growth rate, and life cycle of intertidal organisms, including red algae. In an effort to identify the genes involved in the high-temperature tolerance of Porphyra, we generated 3,979 expression sequence tags (ESTs) from gametophyte thalli of P. seriata Kjellm. under normal growth conditions and high-temperature conditions. A comparison of the ESTs from two cDNA libraries allowed us to identify the high temperature response (HTR) genes, which are induced or up-regulated as the result of high-temperature treatment. Among the HTRs, HTR2 encodes for a small polypeptide consisting of 144 amino acids, which is a noble nuclear protein. Chlamydomonas expressing the Porphyra HTR2 gene shows higher survival and growth rates than the wild-type strain after high-temperature treatment. These results suggest that HTR2 may be relevant to the tolerance of high-temperature stress conditions, and this Porphyra EST data set will provide important genetic information for studies of the molecular basis of high-temperature tolerance in marine algae, as well as in Porphyra.