Xia Y, Nikolau B J, Schnable P S
Department of Zoology and Genetics, Iowa State University, Ames 50011, USA.
Plant Cell. 1996 Aug;8(8):1291-304. doi: 10.1105/tpc.8.8.1291.
Cuticular waxes are complex mixtures of very long chain fatty acids and their derivatives that cover plant surfaces. Mutants of the ECERIFERUM2 (cer2) gene of Arabidopsis condition bright green stems and siliques, indicative of the relatively low abundance of the cuticular wax crystals that comprise the wax bloom on wild-type plants. We cloned the CER2 gene via chromosome walking. Three lines of evidence establish that the cloned sequence represents the CER2 gene: (1) this sequence is capable of complementing the cer2 mutant phenotype in transgenic plants; (2) the corresponding DNA sequence isolated from plants homozygous for the cer2-2 mutant allele contains a sequence polymorphism that generates a premature stop codon; and (3) the deduced CER2 protein sequence exhibits sequence similarity to that of a maize gene (glossy2) that also is involved in cuticular wax accumulation. The CER2 gene encodes a novel protein with a predicted mass of 47 kD. We studied the expression pattern of the CER2 gene by in situ hybridization and analysis of transgenic Arabidopsis plants carrying a CER2-beta-glucuronidase gene fusion that includes 1.0 kb immediately upstream of CER2 and 0.2 kb of CER2 coding sequences. These studies demonstrate that the CER2 gene is expressed in an organ- and tissue-specific manner; CER2 is expressed at high levels only in the epidermis of young siliques and stems. This finding is consistent with the visible phenotype associated with mutants of the CER2 gene. Hence, the 1.2-kb fragment of the CER2 gene used to construct the CER2-beta-glucuronidase gene fusion includes all of the genetic information required for the epidermis-specific accumulation of CER2 mRNA.
角质层蜡质是覆盖植物表面的超长链脂肪酸及其衍生物的复杂混合物。拟南芥ECERIFERUM2（cer2）基因的突变体表现出亮绿色的茎和角果，这表明构成野生型植物蜡质层的角质层蜡质晶体含量相对较低。我们通过染色体步移克隆了CER2基因。三条证据表明克隆的序列代表CER2基因：（1）该序列能够在转基因植物中互补cer2突变体表型；（2）从cer2-2突变等位基因纯合的植物中分离出的相应DNA序列包含一个产生过早终止密码子的序列多态性；（3）推导的CER2蛋白序列与一个也参与角质层蜡质积累的玉米基因（glossy2）的序列相似。CER2基因编码一种预测分子量为47 kD的新型蛋白质。我们通过原位杂交和对携带CER2-β-葡萄糖醛酸酶基因融合体的转基因拟南芥植物的分析来研究CER2基因的表达模式，该融合体包括CER2上游1.0 kb和CER2编码序列0.2 kb。这些研究表明CER2基因以器官和组织特异性方式表达；CER2仅在幼嫩角果和茎的表皮中高水平表达。这一发现与CER2基因突变体的可见表型一致。因此，用于构建CER2-β-葡萄糖醛酸酶基因融合体的CER2基因的1.2 kb片段包含了CER2 mRNA在表皮特异性积累所需的所有遗传信息。
