Characterization of the tandem-arrayed hiC6 genes in Antarctic and temperate strains of Chlorella vulgaris

Abstract

HIC6 is a group-3 late embryogenesis abundant protein found in Chlorella vulgaris. In the Antarctic strain NJ-7 of this unicellular green alga, it is encoded by a tandem array of five hiC6 genes (designated as NJ7hiC6-1, -2, -3, -4 and -5); in the temperate strain UTEX259, it is encoded by four hiC6 genes in tandem (designated as 259hiC6-1, -2, -3 and -4). Except for NJ7hiC6-3 and -4, the encoding regions of all other hiC6 genes differ from each other by 2-19 bp in each strain. Based on RT-PCR and sequencing of total hiC6 cDNA clones, the relative transcript abundance of each hiC6 gene was evaluated. NJ7hiC6-2 and 259hiC6-2 were not expressed or expressed at low levels, whereas 259hiC6-1 and NJ7hiC6-3/4 exhibited the highest hiC6 transcript levels in the respective strains. In vitro assays showed that different isoforms of HIC6 provided almost identical cryoprotection of lactate dehydrogenase. Our studies suggest that the formation of the tandem arrays of hiC6 in Chlorella is a process of gene duplications accompanied by gene expression divergence.