生物谷：大多數(shù)植物和動物的活動以24小時為1周期。然而,，美國和瑞士研究人員表示,，他們通過研究發(fā)現(xiàn)，有一種植物能將自己內(nèi)部生物鐘信號同周圍環(huán)境的信號結(jié)合起來控制自己每天的生長節(jié)奏,。
采用間隔照像技術(shù),，加州大學(xué)UCDavis大學(xué)從事博士后研究的卡尊納芮·諾祖和同事以及瑞士洛桑大學(xué)的同行發(fā)現(xiàn)，擬南芥幼苗每天快速生長一次,，猛長的時間由植物內(nèi)部的生物鐘和陽光來控制,。而陽光作用主要體現(xiàn)在名為PIF4和PIF5這兩種基因上。
研究人員表示,，當(dāng)擬南芥幼苗處于恒定陽光環(huán)境中時,，每天的最快生長期發(fā)生在下午。然而,，當(dāng)將其轉(zhuǎn)移到更接近自然的晝夜周期性環(huán)境中時,，生長最快期推遲了幾個小時,，接近黎明,。在自然界，通常黎明前植物周圍會有更多的水分,。
研究人員證實(shí)，PIF4和PIF5兩種基因同植物的生長相關(guān),，同時受生物鐘的控制,。這兩種基因在白天會“接通”生產(chǎn)蛋白質(zhì)，天黑后“關(guān)閉”,，然后在后半夜再“接通”,。但是，暴露在陽光中時,，PIF4和PIF5生產(chǎn)的蛋白質(zhì)會發(fā)生斷裂,，于是當(dāng)植物內(nèi)部生物鐘在促使基因產(chǎn)生蛋白質(zhì)的同時，外部的陽光則在“消耗”蛋白質(zhì),。
據(jù)悉,，美國國家科學(xué)基金會和瑞士國家科學(xué)基金會是這項(xiàng)研究工作的主要資助機(jī)構(gòu)。相關(guān)研究報告發(fā)表在《自然》雜志網(wǎng)站上。(援引科技日報)
原始出處:
Nature advance online publication 24 June 2007 | doi:10.1038/nature05946; Received 20 January 2007; Accepted 16 May 2007; Published online 24 June 2007
Rhythmic growth explained by coincidence between internal and external cues
Kazunari Nozue1, Michael F. Covington1, Paula D. Duek2,3, Séverine Lorrain2, Christian Fankhauser2, Stacey L. Harmer1 & Julin N. Maloof1
Section of Plant Biology, College of Biological Sciences, University of California, Davis, One Shields Avenue, Davis, California 95616, USA
Center for Integrative Genomics, University of Lausanne, Genopode Building, CH-1015 Lausanne, Switzerland
Present address: Swiss Institute of Bioinformatics, 1 rue Michel Servet, CH-1211 Geneva 4, Switzerland.
Correspondence to: Julin N. Maloof1 Correspondence and requests for materials should be addressed to J.N.M. (Email: [email protected]).
Most organisms use circadian oscillators to coordinate physiological and developmental processes such as growth with predictable daily environmental changes like sunrise and sunset. The importance of such coordination is highlighted by studies showing that circadian dysfunction causes reduced fitness in bacteria1 and plants2, as well as sleep and psychological disorders in humans3. Plant cell growth requires energy and water—factors that oscillate owing to diurnal environmental changes. Indeed, two important factors controlling stem growth are the internal circadian oscillator4, 5, 6 and external light levels7. However, most circadian studies have been performed in constant conditions, precluding mechanistic study of interactions between the clock and diurnal variation in the environment. Studies of stem elongation in diurnal conditions have revealed complex growth patterns, but no mechanism has been described8, 9, 10. Here we show that the growth phase of Arabidopsis seedlings in diurnal light conditions is shifted 8–12 h relative to plants in continuous light, and we describe a mechanism underlying this environmental response. We find that the clock regulates transcript levels of two basic helix–loop–helix genes, phytochrome-interacting factor 4 (PIF4) and PIF5, whereas light regulates their protein abundance. These genes function as positive growth regulators; the coincidence of high transcript levels (by the clock) and protein accumulation (in the dark) allows them to promote plant growth at the end of the night. Thus, these two genes integrate clock and light signalling, and their coordinated regulation explains the observed diurnal growth rhythms. This interaction may serve as a paradigm for understanding how endogenous and environmental signals cooperate to control other processes.
Figure 1: Diurnal rhythms of hypocotyl elongation require light and the circadian clock.
Plants were entrained for three days under short-day conditions and then switched to continuous light (a) or 4L:4D (d). Alternatively, plants were entrained for four days under short-day conditions and then switched to continuous darkness (b) or kept in short-day conditions (c). We used infrared imaging to monitor seedling growth (see Methods). Growth rate is plotted as a function of time; zero indicates dawn of the fourth day. The vertical scale bar indicates 0.1 mm h–1. Measurements were started when hypocotyls were easily discernible, typically t = 8. The mean s.e.m. of at least two independent experiments is shown; n 6 seedlings. In all plot areas, times of true light and darkness are indicated by clear and grey rectangles, respectively; see below for meaning of x axis rectangles. a, Rhythmic elongation of wild-type Col and Wassilewskija (Ws) hypocotyls in continuous light. White and grey bars on the x axis indicate subjective day and night, respectively. b, Continuous hypocotyl elongation of wild-type (WT) Col in continuous darkness. Grey and black bars on the x axis indicate subjective day and night, respectively. c, Hypocotyl elongation in short-day conditions. Col is the wild-type background for CCA1-OX, elf3 and hy2; Landsberg erecta (Ler) is the wild-type background for hy5. d, Growth in 4L:4D conditions is altered in clock mutants. Grey and black rectangles on the x axis indicate subjective day and night, respectively.
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