Molecular cloning and characterization of cold responsive protein AnF48_RPL11 from Antarctic micro green alga AnF48

Abstract

A polar micro green alga, AnF48 was collected from near the King Sejong Station located in King George Island in the Antarctica (62° 13′S 58° 47′W). It is likely an endemic species, closely related to the genus Hematococcus based on 18S and rbcL sequence data. AnF48 successfully proliferated and propagated near 4-10℃, in contrast it showed dramatic growth decrease (up to 50%) when the ambient temperature exceeded 15℃. To discover the genes which are responsible for this specific temperature adaptation, GeneFishing DEG PCR was performed using cDNAs extracted from AnF48 grown at different temperatures (4℃, 15℃, 25℃). Genes induced by low temperature were identified by cloning and sequencing. One of them was a homolog of RPL11 which has been reported as a cold-responsive gene in E. coli. Thus, we named it AnF48_RPL11 (ribosomal protein L11). RT-PCR analysis confirmed that the expression level of AnF48_RPL11 was significantly up-regulated under 4℃ compared with that at 15℃ or 25℃. The full length cDNA sequences of AnF48_RPL11 was obtained using 5' and 3' race. The open reading frame consisted of 544 bp encoding 125 amino acids. It contains four exons and three introns meanwhile Chlamydomonas reinhardtti has seven exons and six introns. To our surprise, the similarity of deduced amino acids of AnF48_RPL11 is higher with RPL11 in Arabidopsis thaliana (92%) than in algal homologues Chlamydomonas reinhardtii (88%). This results suggested cold adaptative mechanism is conserved in a wide range of organism from E. coli to higher plant. We first report RPL11 from Antarctic micro green alga and provide molecular evidence for evolutionary conservation upon cold stimuli.