Rong L J, Karcher S J, Gelvin S B
Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907.
J Bacteriol. 1991 Aug;173(16):5110-20. doi: 10.1128/jb.173.16.5110-5120.1991.
picA is an Agrobacterium tumefaciens chromosomal locus, identified by Mu d11681 mutagenesis, that is inducible by certain acidic polysaccharides found in carrot root extract. Cloning and genetic analysis of a picA::lacZ fusion defined a region of the picA promoter that is responsible for the induction of this locus. Furthermore, we identified a possible negative regulator of picA expression upstream of the picA locus. This sequence, denoted pgl, has extensive homology to polygalacturonase genes from several organisms and inhibited the induction of the picA promoter when present in multiple copies in A. tumefaciens. DNA sequence analysis indicated at least two long open reading frames (ORFs) in the picA region. S1 nuclease mapping was used to identify the transcription initiation site of picA. Mutation of ORF1, but not ORF2, of the picA locus was responsible for an increased aggregation of A. tumefaciens, forming "ropes" in the presence of pea root cap cells. In addition, a potato tuber disk virulence assay indicated that a preinduced picA mutant was more virulent than was the wild-type control, a further indication that the picA locus regulates the surface properties of the bacterium in the presence of plant cells or plant cell extracts.
picA是根癌土壤杆菌的一个染色体位点，通过Mu d11681诱变鉴定，可被胡萝卜根提取物中发现的某些酸性多糖诱导。对picA::lacZ融合体的克隆和遗传分析确定了picA启动子中负责该位点诱导的区域。此外，我们在picA位点上游鉴定了一个可能的picA表达负调控因子。这个序列，称为pgl，与几种生物体的多聚半乳糖醛酸酶基因有广泛的同源性，当在根癌土壤杆菌中以多拷贝存在时，会抑制picA启动子的诱导。DNA序列分析表明picA区域至少有两个长开放阅读框（ORF）。用S1核酸酶作图法确定了picA的转录起始位点。picA位点的ORF1而非ORF2的突变导致根癌土壤杆菌聚集增加，在豌豆根冠细胞存在的情况下形成“绳状物”。此外，马铃薯块茎圆盘毒力试验表明，预诱导的picA突变体比野生型对照更具毒力，这进一步表明picA位点在植物细胞或植物细胞提取物存在的情况下调节细菌的表面特性。
