Molecular mechanisms regulating ethylene biosynthesis in plant

乙烯是一种气态植物激素，控制植物生长和发育的许多方面。1-氨基环丙烷-1-羧酸(ACC)合成酶和ACC氧化酶是高等植物乙烯生物合成途径中的关键酶。甜瓜1-氨基环丙烷-1-羧酸合成酶(CME-ACS2)是甜瓜乙烯生物合成途径中的关键酶，但其表达调控机制尚不清楚。通过酵母单杂交筛选方法，利用CME-ACS2启动子中的GCCGAC序列(DRE/CRT顺式作用元件)分离得到3个甜瓜AP2/ERF转录因子(CME-DREB1、CME-ERF1和CME-ERF2)。我们证明了CME-DREB1与GCCGAC序列强结合，而CME-ERF1和CME-ERF2不与GCCGAC序列结合。瞬时表达分析表明，只有CME-DREB1能通过GCCGAC序列在甜瓜叶片细胞中激活下游报告基因的转录。茉莉酸甲酯(MeJA)提高了CME-ACS2和CME-DREB1在甜瓜叶片中的表达水平。这些结果表明，在茉莉酸存在下，CME-DREB1作为CME-ACS2的转录激活剂发挥作用。

Ethylene is a gaseous plant hormone that controls many aspects of plant growth and development. 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase are key enzymes in ethylene biosynthesis pathway in higher plants. A melon 1-aminocyclopropane-1-carboxylate synthase (CMe-ACS2) is a key enzyme in the ethylene biosynthesis pathway in melon, but mechanisms regulating CMe-ACS2 expression remain to be clarified. We characterized three melon AP2/ERF transcription factors (CMe-DREB1, CMe-ERF1 and CMe-ERF2), which were isolated by a yeast one-hybrid screening method using a GCCGAC sequence (DRE/CRT cis-acting element) in the CMe-ACS2 promoter. We demonstrated that CMe-DREB1 strongly bound to the GCCGAC sequence, but CMe-ERF1 and CMe-ERF2 did not. Transient expression analysis showed that only CMe-DREB1 could activate the transcription of the downstream reporter gene through the GCCGAC sequence in melon leaf cells. The expression levels of CMe-ACS2 and CMe-DREB1 in melon leaves were increased by methyl jasmonate (MeJA) treatment. These results suggest that CMe-DREB1 functions as a transcriptional activator of CMe-ACS2 in the presence of jasmonate.