Relative evolutionary rates of NBS-encoding genes revealed by soybean segmental duplication
Relative evolutionary rates of NBS-encoding genes revealed by soybean segmental duplication
复制标题
大豆片段复制揭示NBS编码基因的相对进化速率
DOI：
10.1007/s00438-010-0587-7
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发表时间：
2011-01-01
影响因子：
3.1
通讯作者：
Chen, Jian-Qun
中科院分区：
文献类型：
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作者：
Zhang, Xiaohui;Feng, Ying;Chen, Jian-Qun
众所周知，编码核苷酸结合位点（NBS）的基因是重复序列丰富且进化速度快的基因。然而，关于串联和节段NBS重复的相对重要性及其确切的进化速率的信息很少。在大豆中发生的两轮大规模重复为研究这些问题提供了独特的机会。对NBS基因与非NBS基因在同义同源序列片段上的比较表明，编码NBS基因的基因进化速度比其侧翼的非NBS基因快1.5倍（同义替换率高~1.5倍，非同义替换率高~2.3倍），基因丢失速度快~2倍。与片段重复相比，串联NBS重复在大豆中更为丰富，说明串联重复是NBS基因扩增的主要驱动力。值得注意的是，在大多数串联重复的NBS基因家族中，检测到显著的序列交换和显著的正选择。结果表明，NBS基因的快速进化可能是多样化选择和频繁的序列交换共同作用的结果。有趣的是，TIR-NBS-LRR基因（tnl）比非tnl具有更高的核苷酸替代率，这表明这些类型的NBS基因可能具有相当不同的进化模式。确定TNL、非TNL和非nbs基因的确切相对进化率是很重要的，以便了解寄主植物在共同进化背景下对快速进化的病原体的反应进行调整的速度有多快。
It is well known that nucleotide binding site (NBS)-encoding genes are duplicate-rich and fast-evolving genes. However, there is little information on the relative importance of tandem and segmental NBS duplicates and their exact evolutionary rates. The two rounds of large-scale duplication that have occurred in soybean provide a unique opportunity to investigate these issues. Comparison of NBS and non-NBS genes on segments of syntenic homoeologs shows that NBS-encoding genes evolve at least 1.5-fold faster (~1.5-fold higher synonymous and ~2.3-fold higher nonsynonymous substitution rates) and lose their genes ~twofold faster than the flanking non-NBS genes. Compared with segmental duplicates, tandem NBS duplicates are more abundant in soybean, suggesting that tandem duplication is the major driving force in the expansion of NBS genes. Notably, significant sequence exchanges along with significantly positive selection were detected in most tandem-duplicated NBS gene families. The results suggest that the rapid evolution of NBS genes may be due to the combined effects of diversifying selection and frequent sequence exchanges. Interestingly, TIR–NBS–LRR genes (TNLs) have a higher nucleotide substitution rate than non-TNLs, indicating that these types of NBS genes may have a rather different evolutionary pattern. It is important to determine the exact relative evolutionary rates of TNL, non-TNL, and non-NBS genes in order to understand how fast the host plant can adjust its response to rapidly evolving pathogens in a coevolutionary context.