苦瓜乙烯受體cDNA之選殖與分析

Cloning and Analysis of Ethylene Receptor cDNA from Bitter Gourd

為了瞭解乙烯對苦瓜果實後熟的調控機制，並進一步運用生物技術控制苦瓜的果實後熟，本研究以阿拉伯芥乙烯受體（ethylene receptor）AtETR1基因片段為探針，篩選苦瓜cDNA庫，得到苦瓜乙烯受體cDNA選殖系pMcER2874，所含cDNA長2,521 bp，對應之基因命名為McERS1。McERS1解碼之蛋白質具有637個胺基酸，推演之分子量為71.06 kDa，等電點為6.37，N端序列具有3個疏水性保守區，推測為跨膜組區，近C端之組胺酸激酶組區上則有乙烯受體五個序列保守區H、N、G、F、及G，且不具磷酸根分子接受區，屬於AtERS1型受體。同源性分析結果顯示，苦瓜McERS1的胺基酸序列與阿拉伯芥乙烯受體AtETR1胺基酸序列之同源性為59.1%，與網紋甜瓜及胡瓜乙烯受體同源性分別高達95.5%及95.1%；McERS1與雙子葉作物ERS1型乙烯受體之序列同源性較高，且同科作物間的ERS1型乙烯受體胺基酸序列同源性較大。 For understanding the mechanism of ethylene on fruit ripening in bitter gourd, a cDNA encoding ethylene receptor was isolated from cDNA library of bitter gourd using part of ethylene receptor AtETR1 gene from Arabidopsis as the probe. The cDNA in clone pMcER2874 consists of 2,521 base pairs and contains an open reading frame of 637 amino acids with a calculated molecular mass of 71.06 kDa and a predicted isoelectric point of 6.37. The coding protein, named McERS1, contains three predicted hydrophobic transmembrane-spanning domains in the N-terminal region. The histidine kinase domain in C terminus possesses 5 conserved motifs ”H, N, G1, F, G2”. The predicted McERS1 protein exhibits 59.1% identity in amino acid sequence with Arabidopsis AtETR1, and exhibits 95.5% and 95.1% identity with ERS1 sequences from Cucumis melo and C. sativus, respectively. The predicted McERS1 protein shares higher amino acid sequence identity with ERS1 type ethylene receptors from dicotyledons than from monocotyledons. Ethylene receptors from plants among the same family or among monocotyledons share higher amino acid sequence identity to each other.