The phytopathogen Pseudomonas syringae subsp. savastanoi incites the production of galls on olive and oleander plants. Gall formation is dependent on bacterial production of the phytohormone indoleacetic acid (IAA). The genetic determinants for IAA synthesis are located on a plasmid (pIAA) and are organized in an operon in oleander strains of the bacterium. P. syringae subsp. savastanoi further converts IAA to an amino acid conjugate, 3-indole-acetyl-epsilon-L-lysine (IAA-lysine). The gene for IAA-lysine synthetase (iaaL) was found on the IAA plasmid by screening pIAA deletion mutants for the ability to convert IAA to IAA-lysine. The iaaL locus was then cloned in the vector pUC8 from a bank of P. syringae subsp. savastanoi EW2009 plasmid DNA to construct recombinant plasmid pLG87. The specific activity of IAA-lysine synthetase in Escherichia coli transformed with pLG87 was 47 times higher than that of the enzyme extract from P. syringae subsp. savastanoi. The direction of transcription of the iaaL gene was determined to be opposite to that of the IAA operon. The location of the iaaL gene on pIAA1 was mapped by Tn5 insertion mutagenesis to a 2.5-kilobase-pair fragment 2 kilobase pairs from the IAA operon.
植物病原体Pseudomonas syringae亚种savastanoi会在橄榄和夹竹桃植物上引起瘤形成。瘤的形成取决于细菌产生的植物激素吲哚乙酸(IAA)。IAA合成的遗传决定因子位于质粒pIAA上,并在细菌的夹竹桃菌株中组织成一个操作子。P. syringae亚种savastanoi进一步将IAA转化为一种氨基酸共轭物,3-吲哚乙酰-ε-L-赖氨酸(IAA-赖氨酸)。通过筛选pIAA缺失突变体的能力将IAA转化为IAA-赖氨酸,找到了IAA-赖氨酸合成酶(iaaL)的基因位于IAA质粒上。然后,iaaL基因在P. syringae亚种savastanoi EW2009质粒DNA库中克隆到pUC8载体中,构建了重组质粒pLG87。转化了pLG87的大肠杆菌中IAA-赖氨酸合成酶的特异活性比P. syringae亚种savastanoi的酶提取物高47倍。iaaL基因的转录方向确定为与IAA操作子相反。通过Tn5插入突变技术将iaaL基因在pIAA1上的位置映射到距离IAA操作子2kb的2.5kb片段上。