Rastogi R, Dulson J, Rothstein S J
Department of Molecular Biology and Genetics, University of Guelph, Ontario, Canada.
Plant Physiol. 1993 Nov;103(3):829-34. doi: 10.1104/pp.103.3.829.
Arginine decarboxylase (ADC) is the first enzyme in one of the two pathways of putrescine biosynthesis in plants. The genes encoding ADC have previously been cloned from oat and Escherichia coli. Degenerate oligonucleotides corresponding to two conserved regions of ADC were used as primers in polymerase chain reaction amplification of tomato (Lycopersicon esculentum Mill.) genomic DNA, and a 1.05-kb fragment was obtained. This genomic DNA fragment encodes an open reading frame of 350 amino acids showing about 50% identity with the oat ADC protein. Using this fragment as a probe, we isolated several partial ADC cDNA clones from a tomato pericarp cDNA library. The 5' end of the coding region was subsequently obtained from a genomic clone containing the entire ADC gene. The tomato ADC gene contains an open reading frame encoding a polypeptide of 502 amino acids and a predicted molecular mass of about 55 kD. The predicted amino acid sequence exhibits 47 and 38% identify with oat and E. coli ADCs, respectively. Gel blot hybridization experiments show that, in tomato, ADC is encoded by a single gene and is expressed as a transcript of approximately 2.2 kb in the fruit pericarp and leaf tissues. During fruit ripening the amount of ADC transcript appeared to peak at the breaker stage. No significant differences were seen when steady-state ADC mRNA levels were compared between normal versus long-keeping Alcobaca (alc) fruit, although alc fruit contain elevated putrescine levels and ADC activity at the ripe stage. The lack of correlation between ADC activity and steady-state mRNA levels in alc fruit suggests a translational and/or posttranslational regulation of ADC gene expression during tomato fruit ripening.
精氨酸脱羧酶（ADC）是植物中腐胺生物合成两条途径之一的首个酶。此前已从燕麦和大肠杆菌中克隆出编码ADC的基因。对应于ADC两个保守区域的简并寡核苷酸用作引物，对番茄（Lycopersicon esculentum Mill.）基因组DNA进行聚合酶链反应扩增，获得了一个1.05 kb的片段。该基因组DNA片段编码一个350个氨基酸的开放阅读框，与燕麦ADC蛋白显示约50%的同一性。以该片段为探针，我们从番茄果皮cDNA文库中分离出几个部分ADC cDNA克隆。随后从包含整个ADC基因的基因组克隆中获得编码区的5'端。番茄ADC基因包含一个开放阅读框，编码一个502个氨基酸的多肽，预测分子量约为55 kD。预测的氨基酸序列与燕麦和大肠杆菌ADC分别具有47%和38%的同一性。凝胶印迹杂交实验表明，在番茄中，ADC由单个基因编码，在果实果皮和叶片组织中表达为约2.2 kb的转录本。在果实成熟过程中，ADC转录本的量似乎在破色期达到峰值。当比较正常果实与耐贮藏Alcobaca（alc）果实的稳态ADC mRNA水平时，未观察到显著差异，尽管alc果实在成熟阶段腐胺水平和ADC活性升高。alc果实中ADC活性与稳态mRNA水平之间缺乏相关性，表明在番茄果实成熟过程中ADC基因表达存在翻译和/或翻译后调控。
