【作者】 陈智忠；

【导师】 巩志忠；

【作者基本信息】 中国农业大学 ， 植物学， 2005， 博士

【摘要】 干旱胁迫是限制世界作物生产的主要环境因子之一。研究植物响应干旱胁迫的细胞和分子机制,能够为植物抗旱的定向育种创造条件。利用植物干旱遗传学筛选体系,我们在拟南芥中分离得到了两类耐旱突变体,在水分胁迫条件下,这些突变体表现出抗旱的表型。其中,一类突变体为lew2（leaf wilting2）,包含两个等位突变体:lew2-1和lew2-2:另一类是abol（ABA overly-sensitive）,包含四个等位突变体:abol—1、abol—2、abol—3和abol—4。 基因定位结果显示lew2的突变基因是AtCesA8/IRX1基因的一个新的等位基因,该基因编码纤维素合成酶复合体的一个亚基。调控着植物体内次生细胞壁纤维素的合成。以前发现的拟南芥中几个位点的隐性突变导致了木质部萎陷的表型,但没有观察到水分运输的缺失。我们发现了lew2突变体的叶子在高蒸腾条件下出现萎焉,而在同样条件下野生型植株不受任何影响。经检测发现lew2植株的茎中流出的伤流量只有野生型的一半,它暗示了lew2植株中由于木质部的萎陷而阻止了水分运输。使植物在正常条件下就处于一种干旱胁迫状态,它可以转换为一种信号诱导植物从形态、生理以及分子水平上采取应急措施,适应这种干旱胁迫。同时,由于植物体内纤维素合成的过程受到阻碍,从而反馈调节上游蔗糖等可溶性糖的积累,使受糖诱导的ABA生物合成基因ABA2/SDR1得以表达。进而增加ABA的合成。ABA作为一种胁迫信号可诱导激活植物体内的渗透调节机制,提高植物的渗透调节能力,以适应这种水分（干旱）胁迫。试验结果表明lew2植株比野生型体内积累的ABA、脯氨酸和可溶性糖要多,而具有较强的耐渗透和干旱胁迫能力。在正常生长条件下,lew2体内的胁迫诱导基因RD29A、P5C5表现为组成性表达,而野生型则表达量少甚至不表达。我们的实验结果表明AtCesA8基因的功能在于防止木质部萎陷以保持植物体内适当的水分运输,调节纤维素与可溶性糖的合成比例以提高植物的渗透调节能力。同时,由木质部萎陷引起的水分运输受阻可以转换为一种信号,从而控制植物保卫细胞的运动和细胞的渗透调节能力,也说明纤维素合成、细胞壁结构对于植物响应干旱、滲透胁迫是一个重要的因子。 abol突变体与植物的水分蒸腾相关。植物激素ABA在调控植物生长、发育和逆境胁迫响应中起着重要的作用。尤其对于干旱胁迫,ABA作为一个信号调控着植物叶片气孔的运动,以减少水分的蒸腾。对于光合作用吸收CO₂、蒸腾作用蒸腾水分来说,由成对的保卫细胞形成气孔是一个重要的过程。在干旱胁迫中,气孔的数量直接影响到植物叶片水分散失量的大小,从而调控着植物的抗旱性能。abol突变体在水分胁迫条件下表现出抗旱的表型。研究发现ABO1基因的突变增加了气孔关闭过程对ABA信号感知的敏感性,加剧了ABA对植物生长的抑制作用。令人惊异的是,ABO1基因也调控着来源于卫星分生母细胞（SMMC）的保卫细胞的生长发育,而对产生于分生母细胞（MMC）的保卫细胞的生长发育则不起作用。利用图位克隆鉴定出ABO1基因编码一个动物IKAP（IkB Kinas-Associated Protein）的同系物蛋白。动物中的IKAP及其酵母中的同系物IKI3/ELP1是一个最大的延伸复合体亚基,在mRNA加工的延伸阶段,它调控着基因的表达。我们的研究结果揭示了在mRNA加工的延伸中ABO1基因调控着保卫细胞的生长发育、植物生长以及气孔运动过程对ABA信号的响应。更多还原

【Abstract】 Drought stress is one of the environmental factor that greatly limit crop production and plant distribution in the world. The study of the cellular and molecular responses of plants to drought stress will help to broaden the possibilities for genetically engineering plants. By means of a genetic screen for different drought responses, we identified two drought-tolerated mutants that showed drought resistant phenotype under water stress conditions in Arabidopsis. One is the lew2 (leaf wilting), the other is the abol (ABA overly-sensitive).Although water transported in the xylem from root to shoot is physiologically studied in higher plants in great detail, little is known of the molecular and genetic control mechanisms. Recessive mutations in several loci of Arabidopsis were previously shown to lead to a collapsed xylem phenotype but water-transport deficiency was not observed. We found that the leaves of lew2 plants wilted easily under high transpiration that did not have any harmful effect on wild-type plants. Map based cloning revealed that the lew2 mutant is a new allele of the AtCesA8/IRX1 gene which encodes a subunit of a cellulose synthesis complex. Cross-sections of stems, roots and leaves showed severely collapsed xylem walls. The flow rate of the transpiration stream of lew2 is slower than that of the wild type, which suggests that water transport is impeded, probably because of its collapsed xylem. In contrast to their leaf-wilting phenotypes, lew2 plants accumulate more ABA, proline and soluble sugars than the wild type and are more tolerant to drought stress as well as to NaCl, mannitol and other osmotic stresses. The expression of one stress-inducible marker gene RD29A, one proline synthesis-related gene P5CS (pyrroline-5-carboxylate synthase) and one ABA synthesis-related gene SDR1 (alcohol dehydrogenase/reductase) were higher in lew2 than in the wild type. Our results suggest that cellulose synthesis is crucial for drought and osmotic stress responses including drought-induction of gene expression.Plant hormone abscisic acid (ABA) plays vital roles in modulating plant growth, development as well as stress responses. Stomata formed by. pairs of guard cells are important accesses for uptake of CO2 for photosynthesis and the evaporation of water during transpiration. The abo1 mutation augments ABA-hypersensitive stomatal closing and increases ABA sensitivity in inhibiting the seedling growth. Fascinatingly, ABO1also modulates development and growth of guard cells originated from satellite meristemoid mother cells, but not from meristemoid mother cells. Mapping based cloning identified ABO1 gene which encodes a homolog of animal IKAP (IkB Kinase-Associated Protein) protein. IKAP in animals or its homolog IKI3/ELP1 in yeast is the largest subunit of Elongator complex that controls gene expression at the elongating stage of mRNA processing. Our results uncover crucial roles for ABO1 in regulating mRNA processing for modulating the growth of guard cells and controlling stomatal movement in responding to ABA.更多还原