Microalgal ice-binding proteins (IBPs) in the polar region are poorly understood at the genome-wide level, although they are important for cold adaptation. Through the transcriptome study with the Arctic green alga Chloromonas sp. KNF0032, we identified six Chloromonas IBP genes (CmIBPs), homologous with the previously reported IBPs from Antarctic snow alga CCMP681 and Antarctic Chloromonas sp. They were organized with multiple exon/intron structures and low-temperature-responsive cis-elements in their promoters and abundantly expressed at low temperature. The biological functions of three representative CmIBPs (CmIBP1, CmIBP2 and CmIBP3) were tested using in vitro analysis and transgenic plant system. CmIBP1 had the most effective ice recrystallization inhibition (IRI) activities in both in vitro and transgenic plants, and CmIBP2 and CmIBP3 had followed. All transgenic plants grown under nonacclimated condition were freezing tolerant, and especially 35S::CmIBP1 plants were most effective. After cold acclimation, only 35S::CmIBP2 plants showed slightly increased freezing tolerance. Structurally, the CmIBPs were predicted to have β-solenoid forms with parallel β-sheets and repeated TXT motifs. The repeated TXT structure of CmIBPs appears similar to the AidA domain-containing adhesin-like proteins from methanogens. We have shown that the AidA domain has IRI activity as CmIBPs and phylogenetic analysis also supported that the AidA domains are monophyletic with ice-binding domain of CmIBPs, and these results suggest that CmIBPs are a type of modified adhesins.

中文翻译：

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从北极微藻中分离出的II型冰结合蛋白类似于粘附素蛋白，并提高了转基因植物的耐冻性。

尽管在冷适应中很重要，但在全基因组水平上对极区的微藻冰结合蛋白（IBPs）知之甚少。通过与北极绿藻Chloromonas sp。的转录组研究。KNF0032，我们鉴定了六个绿单胞菌IBP基因（CmIBPs），与先前报道的南极雪藻CCMP681和南极绿单胞菌sp。的IBP同源。它们在启动子中具有多个外显子/内含子结构和低温响应顺式元件，并在低温下大量表达。使用体外分析和转基因植物系统测试了三种代表性CmIBP（CmIBP1，CmIBP2和CmIBP3）的生物学功能。CmIBP1在体外和转基因植物中均具有最有效的冰重结晶抑制（IRI）活性，紧随其后的是CmIBP2和CmIBP3。在非适应条件下生长的所有转基因植物均耐冷冻，尤其是35S :: CmIBP1植物最有效。冷驯化后，仅35S :: CmIBP2植物显示出稍高的抗冻性。在结构上，CmIBPs被预测为具有平行的β-折叠和重复的TXT基序的β-电磁体形式。CmIBPs的重复TXT结构看起来与产甲烷菌中含有AidA域的粘附素样蛋白相似。我们已经显示，AidA结构域具有CmIBPs的IRI活性，并且系统发育分析还支持AidA结构域与CmIBPs的冰结合域是单系的，这些结果表明CmIBPs是一种修饰的粘附素。：CmIBP1植物最有效。冷驯化后，仅35S :: CmIBP2植物显示出稍高的抗冻性。在结构上，CmIBPs被预测为具有平行的β-折叠和重复的TXT基序的β-电磁体形式。CmIBPs的重复TXT结构看起来类似于产甲烷菌中含有AidA域的粘附素样蛋白。我们已经显示，AidA结构域具有CmIBPs的IRI活性，并且系统发育分析还支持AidA结构域与CmIBPs的冰结合域是单系的，这些结果表明CmIBPs是一种修饰的粘附素。：CmIBP1植物最有效。冷驯化后，仅35S :: CmIBP2植物显示出稍高的抗冻性。在结构上，CmIBPs被预测为具有平行的β-折叠和重复的TXT基序的β-电磁体形式。CmIBPs的重复TXT结构看起来类似于产甲烷菌中含有AidA域的粘附素样蛋白。我们已经显示，AidA结构域具有CmIBPs的IRI活性，并且系统发育分析还支持AidA结构域与CmIBPs的冰结合域是单系的，这些结果表明CmIBPs是一种修饰的粘附素。CmIBPs的重复TXT结构看起来类似于产甲烷菌中含有AidA域的粘附素样蛋白。我们已经显示，AidA结构域具有CmIBPs的IRI活性，并且系统发育分析还支持AidA结构域与CmIBPs的冰结合域是单系的，这些结果表明CmIBPs是一种修饰的粘附素。CmIBPs的重复TXT结构看起来类似于产甲烷菌中含有AidA域的粘附素样蛋白。我们已经显示，AidA结构域具有CmIBPs的IRI活性，并且系统发育分析还支持AidA结构域与CmIBPs的冰结合域是单系的，这些结果表明CmIBPs是一种修饰的粘附素。