State Key laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei 430072, China.
Gene. 2011 Aug 15;482(1-2):51-8. doi: 10.1016/j.gene.2011.05.006. Epub 2011 May 24.
An Antarctic strain (NJ-7) of Chlorella vulgaris possesses the same 18S rRNA sequence as that of a temperate strain (UTEX259), but shows significantly higher freezing tolerance than the latter. Suppression subtractive hybridization (SSH) was performed to identify genes of intensified expression in NJ-7 relative to UTEX259. Among the genes identified, Ccor1 and Ccor2, co-organized in the same gene cluster Ccor1-Ccor2-Ccor1-Ccor2, showed much higher expression levels in NJ-7 than in UTEX259 at both 20°C and 4°C. As detected by Northern blot and Western blot analyses, the two genes were cold-inducible in NJ-7 but almost not expressed in UTEX259. Their encoded products are predicted to share 55.7% identity to each other and possess physicochemical characteristics similar to that of late embryogenesis abundant (LEA) proteins in plants. The purified recombinant Ccor1 and Ccor2 showed high heat-stability and could act as cryoprotectants to lactate dehydrogenase in vitro. Based on their expression patterns and protein characteristics, we propose that Ccor1 and Ccor2 are two novel LEA proteins and are related to the greatly enhanced freezing tolerance in the Antarctic strain.
一种南极小球藻（NJ-7）菌株具有与温带小球藻（UTEX259）相同的 18S rRNA 序列，但比后者具有更高的抗冻能力。采用抑制性消减杂交（SSH）技术鉴定了 NJ-7 中相对于 UTEX259 表达增强的基因。在所鉴定的基因中，Ccor1 和 Ccor2 共同组织在同一个基因簇 Ccor1-Ccor2-Ccor1-Ccor2 中，在 20°C 和 4°C 时，其在 NJ-7 中的表达水平明显高于 UTEX259。通过 Northern blot 和 Western blot 分析检测到，这两个基因在 NJ-7 中是冷诱导的，但在 UTEX259 中几乎不表达。它们编码的产物彼此之间具有 55.7%的同源性，具有与植物中晚期胚胎发生丰富（LEA）蛋白相似的理化特性。纯化的重组 Ccor1 和 Ccor2 表现出高热稳定性，并可在体外作为乳酸脱氢酶的保护剂。基于它们的表达模式和蛋白质特性，我们提出 Ccor1 和 Ccor2 是两种新的 LEA 蛋白，与南极菌株中增强的抗冻能力有关。
