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CONSTANS(CO)基因是植物响应光周期调控的重要基因,位于生物钟的输出途径上,能正调控下游开花基因SOC1和FT,进而调控植物开花。PUTTERILL等[1]首先在拟南芥Arabidopsis thaliana中分离出CO基因,反转录PCR(RT-PCR)检测到CO基因在根和叶中表达。ONOUCHI等[2]对花椰菜Brassica oleracea花叶病毒35S(Cauliflower mosaic virus 35S, CaMV 35S)融合CO(35S::CO)转化拟南芥研究发现,CO蛋白会诱导早花和丧失光周期敏感性。进一步研究发现[3],CO在染色体上的位置介于生物节律钟基因和下游开花基因之间,可将光信号转变为开花信号。对拟南芥CO基因过表达研究[1]发现,CO基因过表达的植株比野生型提前开花,表明CO蛋白的活性决定开花时间;但这种调控在不同成员间并不一致,过表达COL1和COL2对植株开花时间没有影响[4],过表达COL9则导致开花延迟,但COL9缺失突变体在长日照下又表现为早花,说明COL9不但抑制CO基因表达调控开花时间,同时下调FT的表达水平从而延迟成花转变[5]。COL3在拟南芥光形态建成时起正调控作用,促进侧根生长和花色素苷积累,并调节长日照敏感植物的花芽分化[6]。从形态来看,CO基因常以多拷贝的形式存在,如拟南芥的CO家族有17个成员[7],水稻Oryza sativa中有16个成员[8],甘蓝型油菜Brassica napus中也克隆到4个CO同源基因[9]。但各CO家族成员的功能存在明显差异。葡萄Vitis vinifera的VvCOL1主要在芽休眠过程中起作用,表明该基因参与光周期,控制芽休眠的诱导和维持[10]。拟南芥中过表达衣藻Chlamydomonas reinhardtii的CrCO会表现出早花表型,结合衣藻的研究发现:CrCO对淀粉的合成和细胞分裂有调节功能,推测CO在高等植物中可能仍保持调节淀粉合成[11]。大麦Hordeum vulgare的HvCO1和Hd1基因与CO亲缘关系最近,可以通过激活HvFT1诱导大麦开花[8],但在转基因拟南芥中则丢失该功能[12]。拟南芥co突变体过表达牵牛花Ipomoea nil的PnCO基因可促进植物开花[13]。黑麦草Lolium perenne的LpCO可以互补拟南芥co突变体的晚花表型[14],甜菜Beta vulgaris的BvCO1可以修复拟南芥co-2突变体的晚花表型[15]。大豆Glycine max的GmCO9影响根的发育,与种子的成熟密切相关[16]。毛果杨Populus trichocarpa的PtCO促使植株提前开花,也可调控植株的生长和芽的分化[17]。本研究以14个已被测序的物种为试验材料,通过生物信息学手段,从外显子-内含子结构、基因重复、基因差异表达分析等3个方面开展CO家族研究,为探讨不同家族成员的潜在功能提供依据。
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