Nature：杂交优势的机制基础

多倍性（或称整基因组复制）是植物中常见的一种演化创新。几种主要作物（包括小麦、棉花和油菜）是异源多倍体，含有两个或多个趋异的基因组，而且一些植物也以种内和种间杂交体的形式存在。这样的植物会有旺盛的生长现象。
美国得克萨斯大学与中国农业大学的研究小组通过对两种拟南芥植物（Arabidopsis thaliana 和 A. arenosa.）的杂交体所做的一项研究为了解杂交体生长能力增强的机制基础提供了线索。研究表明，生物节律时钟的表观基因调制在异源多倍体中调节光合作用通道及淀粉代谢通道中的基因表达。因此，它们比其父辈积累更多叶绿素，产生更多淀粉，而且长得更大。所以，杂交体和异源多倍体植物似乎能通过可逆调整生物节律时钟调控因子而从生理及代谢通道的控制中获得优势，以更好利用白天的时间。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 457, 327-331 (15 January 2009) doi:10.1038/nature07523
Altered circadian rhythms regulate growth vigour in hybrids and allopolyploids
Zhongfu Ni1,6,7, Eun-Deok Kim1,6, Misook Ha1,2,3, Erika Lackey1, Jianxin Liu1, Yirong Zhang1,7, Qixin Sun5 & Z. Jeffrey Chen1,2,3,4
1 Section of Molecular Cell and Developmental Biology,2 Institute for Cellular and Molecular Biology,3 Center for Computational Biology and Bioinformatics, and,4 Section of Integrative Biology, The University of Texas at Austin, One University Station, A-4800, Austin, Texas 78712, USA5 Department of Plant Genetics and Breeding, China Agricultural University, Yuanmingyuan Xilu No. 2, Beijing, 100094, China6 These authors contributed equally to this work.
Segregating hybrids and stable allopolyploids display morphological vigour1, 2, 3, and Arabidopsis allotetraploids are larger than the parents Arabidopsis thaliana and Arabidopsis arenosa 1, 4—the mechanisms for this are unknown. Circadian clocks mediate metabolic pathways and increase fitness in animals and plants5, 6, 7, 8. Here we report that epigenetic modifications of the circadian clock genes CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY)9, 10, 11 and their reciprocal regulators TIMING OF CAB EXPRESSION 1 (TOC1) and GIGANTEA (GI)10, 12, 13 mediate expression changes in downstream genes and pathways. During the day, epigenetic repression of CCA1 and LHY induced the expression of TOC1, GI and downstream genes containing evening elements14 in chlorophyll and starch metabolic pathways in allotetraploids and F1 hybrids, which produced more chlorophyll and starch than the parents in the same environment. Mutations in cca1 and cca1 lhy and the daily repression of cca1 by RNA interference (RNAi) in TOC1::cca1(RNAi) transgenic plants increased the expression of downstream genes and increased chlorophyll and starch content, whereas constitutively expressing CCA1 or ectopically expressing TOC1::CCA1 had the opposite effect. The causal effects of CCA1 on output traits suggest that hybrids and allopolyploids gain advantages from the control of circadian-mediated physiological and metabolic pathways, leading to growth vigour and increased biomass.