中美科学家近日研究发现，杂交植物比其亲本生长更大更好的原因在于，它们负责光合作用和淀粉代谢的基因在白天要更为活跃。这一发现在农业生产中将具有重要的意义。相关论文11月23日在线发表于《自然》（Nature）杂志上。
科学家早已知道，诸如杂交玉米等杂交植物比它们的亲本更为健壮，产量更高，种子更大。在多倍体植物中也具有类似的现象，超过70%的开花植物都是天然的多倍体。然而，科学家一直未能理解其中的分子机制。
在最新的研究中，中国农业大学的Jeffrey Chen和合作者利用拟南芥研究发现，在杂交植物和多倍体植物中，与光合作用和淀粉代谢有关的基因的表达得到了增加，在白天的时候，表达量是其亲本的好几倍。杂交植物和多倍体植物表现出更多的光合作用、叶绿素和淀粉积聚，所有这些导致植株更加高大。
在进一步的研究中，研究人员在杂交植物和多倍体植物中发现了生理时钟调节子和生长势（growth vigor）之间的直接联系。生理时钟控制着植物和动物的生长、代谢和适切性。研究人员发现，在白天的时候，杂交植物和多倍体植物中的一些调节子——转录抑制子被更多地抑制，导致光合作用和淀粉积聚增加。
Chen说：“在此次发现之前，没人真正知道杂交和多倍性怎样增加生长势，这肯定不是这种现象背后的唯一机制，但它是一个巨大的进步。”
他表示，利用这一发现，他们现在可以开发基因组和生物技术工具，以发现和培育更好的杂交和多倍体植物。他说：“我们可以考虑在亲本中筛选这些基因，并选择一些来培育最好的杂交种。这可以通过传统的培养技术来实现，并将在提高燃料作物和粮食作物产量方面产生巨大影响。”（生物谷Bioon.com）
生物谷推荐原始出处：
Nature，doi:10.1038/nature07523，Zhongfu Ni，Z. Jeffrey Chen
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, USA
5 Department of Plant Genetics and Breeding, China Agricultural University, Yuanmingyuan Xilu No. 2, Beijing, 100094, China
6 These authors contributed equally to this work.
7 Present address: Department of Plant Genetics and Breeding, China Agricultural University, Yuanmingyuan Xilu No. 2, Beijing, 100094, China.
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.
