Rose Laura E, Michelmore Richard W, Langley Charles H
The Center for Population Biology, University of California, Davis, California 95616.
Genetics. 2007 Mar;175(3):1307-19. doi: 10.1534/genetics.106.063602. Epub 2006 Dec 18.
Disease resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) in the host species Lycopersicon esculentum, the cultivated tomato, and the closely related L. pimpinellifolium is triggered by the physical interaction between the protein products of the host resistance (R) gene Pto and the pathogen avirulence genes AvrPto and AvrPtoB. Sequence variation at the Pto locus was surveyed in natural populations of seven species of Lycopersicon to test hypotheses of host-parasite coevolution and functional adaptation of the Pto gene. Pto shows significantly higher nonsynonymous polymorphism than 14 other non-R-gene loci in the same samples of Lycopersicon species, while showing no difference in synonymous polymorphism, suggesting that the maintenance of amino acid polymorphism at this locus is mediated by pathogen selection. Also, a larger proportion of ancestral variation is maintained at Pto as compared to these non-R-gene loci. The frequency spectrum of amino acid polymorphisms known to negatively affect Pto function is skewed toward low frequency compared to amino acid polymorphisms that do not affect function or silent polymorphisms. Therefore, the evolution of Pto appears to be influenced by a mixture of both purifying and balancing selection.
栽培番茄（Lycopersicon esculentum）及其近缘种小花番茄（L. pimpinellifolium）对细菌性病原菌丁香假单胞菌番茄致病变种（Pseudomonas syringae pv. tomato, Pst）的抗病性是由宿主抗性（R）基因Pto的蛋白产物与病原菌无毒基因AvrPto和AvrPtoB之间的物理相互作用引发的。对番茄属七个物种的自然种群中Pto基因座的序列变异进行了调查，以检验宿主-寄生虫协同进化和Pto基因功能适应性的假设。在番茄属物种的相同样本中，Pto显示出比其他14个非R基因座显著更高的非同义多态性，而同义多态性没有差异，这表明该基因座氨基酸多态性的维持是由病原体选择介导的。此外，与这些非R基因座相比，Pto保留了更大比例的祖先变异。与不影响功能的氨基酸多态性或沉默多态性相比，已知对Pto功能有负面影响的氨基酸多态性的频率谱向低频倾斜。因此，Pto的进化似乎受到纯化选择和平衡选择的共同影响。
