Arnold Dawn L, Jackson Robert W, Fillingham A Jane, Goss Susan C, Taylor John D, Mansfield John W, Vivian Alan
Centre for Research in Plant Science, Faculty of Applied Sciences, University of the West of England, Coldharbour Lane, Bristol BS16 1QY, UK1.
Department of Biological Sciences, Imperial College, Wye, Ashford, Kent TN25 5AH, UK2.
Microbiology (Reading). 2001 May;147(Pt 5):1171-1182. doi: 10.1099/00221287-147-5-1171.
DNA sequences flanking two avr genes (avrPpiA1 and avrPpiB1) from Pseudomonas syringae pv. pisi show a high degree of similarity. Specific primers designed from the conserved regions were used in PCR amplifications with all P. syringae pv. pisi races. As well as amplifying the expected avrPpiA- and avrPpiB-containing fragments, two additional fragments were amplified: one contained a single open reading frame (ORF1) and was found in races of genomic group II (2, 3A, 4A and 6); the second fragment contained two open reading frames (ORF2 and ORF3), separated by 658 nt, and was detected in all races. All three ORFs had G+C ratios (46.9-48 mol%) that were significantly less than that for P. syringae and each was preceded by a potential hrp box promoter. In P. syringae pv. phaseolicola, ORF1 and ORF2 each elicited a strong non-host hypersensitive reaction on bean leaves; ORF1 was designated avrPpiG, the product of which had strong similarity to AvrRxv, AvrBsT and YopP. ORF2 was identical to a gene, designated avrPpiC, previously isolated from P. syringae pv. pisi race 5. ORF3 was always found in association with avrPpiC and both were detected in a wide range of P. syringae pathovars. In contrast, avrPpiG was only detected in strains of P. syringae pv. pisi genomic group II and P. syringae pv. coronafaciens (ICMP 3113). In P. syringae pv. pisi, avrPpiG was plasmid-borne and avrPpiC and ORF3 were chromosomal. This conservation of flanking sequences has implications for the horizontal transfer of avirulence and virulence genes, suggesting that specific regions of the bacterial genome act as sites for their integration/excision.
来自豌豆丁香假单胞菌的两个无毒基因（avrPpiA1和avrPpiB1）侧翼的DNA序列显示出高度的相似性。从保守区域设计的特异性引物用于所有豌豆丁香假单胞菌小种的PCR扩增。除了扩增出预期的含avrPpiA和avrPpiB的片段外，还扩增出另外两个片段：一个含有单个开放阅读框（ORF1），在基因组第二组小种（2、3A、4A和6）中发现；第二个片段含有两个开放阅读框（ORF2和ORF3），间隔658个核苷酸，在所有小种中均检测到。所有三个开放阅读框的G+C含量（46.9 - 48摩尔%）均显著低于丁香假单胞菌，且每个开放阅读框之前都有一个潜在的hrp框启动子。在菜豆丁香假单胞菌中，ORF1和ORF2在菜豆叶片上均引发强烈的非寄主过敏反应；ORF1被命名为avrPpiG，其产物与AvrRxv、AvrBsT和YopP有很强的相似性。ORF2与一个先前从豌豆丁香假单胞菌小种5中分离出的名为avrPpiC的基因相同。ORF3总是与avrPpiC一起被发现，且在多种丁香假单胞菌致病变种中均被检测到。相比之下，avrPpiG仅在豌豆丁香假单胞菌基因组第二组菌株和燕麦丁香假单胞菌（ICMP 3113）中检测到。在豌豆丁香假单胞菌中，avrPpiG是质粒携带的，而avrPpiC和ORF3是染色体携带的。侧翼序列的这种保守性对无毒和毒力基因的水平转移有影响，表明细菌基因组的特定区域是它们整合/切除的位点。
