Differential gene expression of an Antarctic Chlorella in response to temperature stress

Changes in gene expression are an important response of Antarctic algae to temperature stress. The objective of this study was to investigate the differential gene expression of the Antarctic alga Chlorella UMACC 234 in response to temperature stress. The RNA was extracted from the cells grown at 4, 20, and 30A degrees C and converted to cDNA by reverse transcription. Differentially expressed genes (DEG) were isolated and identified using the GeneFishing (TM) DEG Kit (Seegene) with 20 arbitrary annealing control primers (ACP). The bands of interest were excised and purified from the agarose gel and then cloned and sequenced. A total of 22 DEG clones were isolated and identified, with 11 DEG detected only at 30A degrees C and six DEG detected only at 4A degrees C. Three DEG were detected at 4 and 20A degrees C while two were detected at 20 and 30A degrees C. The DEG were associated with functions such as photosynthesis, carbohydrate metabolism, electron transfer, and cell maintenance. Three DEG that showed high degree of similarity with sequences from the database were those code for Photosystem II P680 chlorophyll a apoprotein CP47 (PSII-CP47), aldose 1-epimerase, and a putative oxidoreductase. Real-time PCR analysis showed that the expression of the PSII-CP47 gene increased by threefold at 4A degrees C while that of the aldose 1-epimerase and oxidoreductase genes increased by threefold and eightfold, respectively, at 30A degrees C compared with 20A degrees C (optimal growth temperature).