Kalendar R, Tanskanen J, Immonen S, Nevo E, Schulman A H
Institute of Biotechnology, University of Helsinki, Plant Genomics Laboratory, Viikki Biocenter, P.O. Box 56, FIN-00014 Helsinki, Finland.
Proc Natl Acad Sci U S A. 2000 Jun 6;97(12):6603-7. doi: 10.1073/pnas.110587497.
The replicative spread of retrotransposons in the genome creates new insertional polymorphisms, increasing retrotransposon numbers and potentially both their share of the genome and genome size. The BARE-1 retrotransposon constitutes a major, dispersed, active component of Hordeum genomes, and BARE-1 number is positively correlated with genome size. We have examined genome size and BARE-1 insertion patterns and number in wild barley, Hordeum spontaneum, in Evolution Canyon, Lower Nahal Oren, Mount Carmel, Israel, along a transect presenting sharply differing microclimates. BARE-1 has been sufficiently active for its insertional pattern to resolve individuals in a way consonant with their ecogeographical distribution in the canyon and to distinguish them from provenances outside the canyon. On both slopes, but especially on the drier south-facing slope, a simultaneous increase in the BARE-1 copy number and a decrease in the relative number lost through recombination, as measured by the abundance of solo long terminal repeats, appear to have driven the BARE-1 share of the genome upward with the height and dryness of the slope. The lower recombinational loss would favor maintenance of more full-length copies, enhancing the ability of the BARE-1 family to contribute to genome size growth. These local data are consistent with regional trends for BARE-1 in H. spontaneum across Israel and therefore may reflect adaptive selection for increasing genome size through retrotransposon activity.
逆转录转座子在基因组中的复制性传播会产生新的插入多态性，增加逆转录转座子的数量，并可能增加它们在基因组中的占比以及基因组大小。BARE-1逆转录转座子是大麦基因组的一个主要的、分散的、活跃的组成部分，并且BARE-1的数量与基因组大小呈正相关。我们在以色列卡梅尔山奥伦谷下游进化峡谷的野生大麦（Hordeum spontaneum）中，沿着呈现出截然不同微气候的样带，研究了基因组大小、BARE-1的插入模式和数量。BARE-1的活性足够高，其插入模式能够以一种与其在峡谷中的生态地理分布相一致的方式区分个体，并将它们与峡谷外的种源区分开来。在两个山坡上，尤其是在较干燥的朝南山坡上，BARE-1拷贝数的同时增加以及通过单长末端重复序列的丰度衡量的因重组而丢失的相对数量的减少，似乎随着山坡的高度和干燥程度推动了BARE-1在基因组中的占比上升。较低的重组损失将有利于维持更多的全长拷贝，增强BARE-1家族对基因组大小增长的贡献能力。这些局部数据与以色列野生大麦中BARE-1的区域趋势一致，因此可能反映了通过逆转录转座子活性增加基因组大小的适应性选择。
