Kuang Hanhui, Ochoa Oswaldo E, Nevo Eviatar, Michelmore Richard W
Department of Plant Science and Genome Center, University of California, Davis, CA 95616, USA.
Plant J. 2006 Jul;47(1):38-48. doi: 10.1111/j.1365-313X.2006.02755.x. Epub 2006 Jun 7.
Resistance genes can exhibit heterogeneous patterns of variation. However, there are few data on their frequency and variation in natural populations. We analysed the frequency and variation of the resistance gene Dm3, which confers resistance to Bremia lactucae (downy mildew) in 1033 accessions of Lactuca serriola (prickly lettuce) from 49 natural populations. Inoculations with an isolate of Bremia lactucae carrying avirulence gene Avr3 indicated that the frequency of Dm3 in natural populations of L. serriola was very low. Molecular analysis demonstrated that Dm3 was present in only one of the 1033 wild accessions analysed. The sequence of the 5' region of Dm3 was either highly conserved among accessions, or absent. In contrast, frequent chimeras were detected in the 3' leucine-rich repeat-encoding region. Therefore low frequency of the Dm3 specificity in natural populations was due to either the recent evolution of Dm3 specificity, or deletions of the whole gene as well as variation in 3' region caused by frequent gene conversions. This is the most extensive analysis of the prevalence of a known disease resistance gene to date, and indicates that the total number of resistance genes in a species may be very high. This has implications for the scales of germplasm conservation and exploitation of sources of resistance.
抗性基因可呈现出异质性的变异模式。然而，关于它们在自然种群中的频率和变异的数据却很少。我们分析了抗性基因Dm3在来自49个自然种群的1033份刺莴苣（Lactuca serriola）材料中的频率和变异情况，该基因赋予对莴苣盘梗霉（霜霉病）的抗性。用携带无毒基因Avr3的莴苣盘梗霉分离株进行接种试验表明，Dm3在刺莴苣自然种群中的频率非常低。分子分析显示，在所分析的1033份野生材料中，只有一份存在Dm3。Dm3 5'区域的序列在材料间要么高度保守，要么缺失。相比之下，在3'富含亮氨酸重复序列编码区域检测到频繁出现的嵌合体。因此，自然种群中Dm3特异性频率低是由于Dm3特异性的近期进化，或者是整个基因的缺失以及频繁的基因转换导致3'区域的变异。这是迄今为止对已知抗病基因流行情况最广泛的分析，并表明一个物种中抗性基因的总数可能非常高。这对种质资源保护规模和抗性资源的利用具有重要意义。
