【作者】 杨丽；

【导师】 巩志忠；

【作者基本信息】 中国农业大学 ， 植物学， 2014， 博士

【摘要】 脱落酸(ABA)在调控植物的生长发育以及生物和非生物胁迫应激反应中都发挥重要作用。ABA可以刺激活性氧(ROS)的生成。在干旱、高盐等环境胁迫下,活性氧的积累能极大地影响植物的生长发育。虽然高浓度的活性氧会对细胞产生损伤,但是在低浓度时,活性氧可作为信号分子调节气孔的开闭,防止病原体的侵入,促进细胞的程序性死亡,改变植株的生长方向等。除此之外,ABA和活性氧在调控植物根生长和发育方面也发挥重要的作用。本文筛选得到ABA敏感突变体abo8(ABA overly sensitive8)。abo8突变体种子萌发和根生长对ABA敏感。AB08基因主要在主根尖、侧根尖和侧根原基中大量表达。AB08编码一个PPR蛋白,定位在线粒体,负责线粒体电子传递链复合体I nad4亚基mRNA的第三个内含子的剪接。线粒体功能紊乱导致abo8突变体的根尖与野生型相比积累了较多活性氧。外源ABA处理同样会提高野生型和突变体根尖活性氧的水平。在培养基中添加还原剂谷胱甘肽(GSH)可部分恢复突变体种子萌发和根生长对ABA的敏感性,这表明abo8种子萌发和根生长对ABA的敏感性是由于突变体体内活性氧的高水平积累造成的。活性氧在调节植物生长发育中起信号分子的作用,但具体分子作用机理尚不清楚。低水平表达的proDR5::GUS和proIAA2::GUS,表明abo8突变体中生长素的积累或信号降低了。外源ABA处理会进一步加剧这种反应,而施加一定浓度的还原剂GSH可以诱导野生型根尖proDR5::GUS的表达,并部分恢复abo8突变或ABA处理对proDR5::GUS表达地抑制。在植物根尖,吲哚乙酸(Indole-3-acetic acid, IAA)会被氧化为活性很低的2-吲哚酮-3-乙酸(2-oxindole-3-acetic acid, OxIAA)。本文因此推测abo8中高水平的活性氧积累导致了根尖生长素的积累或信号水平下降。进一步研究发现,abo8突变会降低植物根分生组织的活性。abo8突变体根尖分生区细胞数目减少并且细胞膨大,根冠柱干细胞分化受到抑制。外源ABA处理抑制野生型根分生组织的活性并加重突变体的表型。施加一定浓度的还原剂GSH可以部分恢复突变体根分生区的缺陷和对ABA的敏感性。本研究还发现,abo8突变或ABA处理抑制PLETHORA1(PLT1)和PLT2的表达,并且这种抑制可以被施加一定浓度的还原剂GSH部分恢复。突变体pltl和plt2的根生长对ABA敏感。abo8、plt1和abo8/plt1双突变体根分生区细胞数目相近,而abo8/plt1双突变体根冠柱干细胞的表型与pltl一致。三突变体abo8/plt1/plt2根分生区的表型则与pltl/plt2相同。另外,诱导PLT2的大量表达可以很大程度恢复abo8突变体根分生组织的表型缺陷和对ABA的敏感性。以上证据表明ABA和活性氧可能通过降低PLT基因的表达抑制根尖分生组织的活性。综合上述结果表明,ABA诱导活性氧的产生并通过调控根尖生长素的应答以及PLT的表达调节根尖分生组织的活性,进而调控植物根的生长和发育。更多还原

【Abstract】 Abscisic acid (ABA) plays crucial roles in plant growth and development, as well as in plant responses to abiotic and biotic stress. ABA can stimulate the production of reactive oxygen species (ROS), which greatly influence plant growth and development under environmental stresses such as water deficiency and high salinity. Although hazardous to cells when exceeded, ROS at low concentrations are important signaling molecules that regulate stomatal movement, prevent pathogen invasion, promote programmed cell death, and redirect plant growth. Besides. ABA and ROS also regulate root growth.abo8(ABA overly sensitive8) mutant was isolated in a genetic screen, for its hypersensitivity to ABA in root growth and seed germination. ABO8, encoding a mitochondria-localized pentatricopeptide repeat (PPR) protein, is responsible for the splicing of nad4intron3. ABO8is highly expressed in primary and lateral root tips, as well as in lateral root primordia. Mitochondrial dysfunction in abo8leads to higher accumulation of ROS in the root tips of abo8than in those of wild type (WT). ABA also stimulates ROS production both in WT and abo8. Addition of the reducing agent GSH partially recovers the hypersensitivity of abo8to ABA in seed germination and root growth. These results indicate that the hypersensitivity to ABA of abo8in root growth and seed germination is caused by the high accumulation of ROS.The molecular mechanism of ROS in regulating plant growth remains obscure. As indicated by low expression level of proDR5::GUS and proIAA2::GUS, auxin accumulation/signaling is reduced in abo8, which is further downregulated by ABA treatment. Addition of GSH induces the expression of proDR5::GUS in WT, and partially recovers the low expression of proDR5::GUS in abo8. The active auxin indole-3-acetic acid (IAA) can be oxidized into the less active form of2-oxindole-3-acetic acid (OxIAA) in root tips, we thus infer that the highly accumulated ROS were responsible for the reduced auxin accumulation/signaling in the root tips of abo8.Further studies showed that the root meristem activity of abo8decreased, containing short meristem with bigger cells and more columella stem cell (CSC) layers. These phenotypes can be aggravated by ABA treatment while partially recovered by GSH treatment. Further more, ABA treatment and abo8mutation both inhibit the expression of PLETHORA1(PLT1) and PLT2, which is also partially recovered by GSH addition. Compared with WT, root growth in plt1and plt2mutants are more sensitive to ABA. abo8, plt1and abo8/plt1generate a similar number of meristem cells, while the CSC phenotype of abo8/plt1double mutant is similar as plt1. The phenotype of triple mutant abo8/plt1/plt2resembles plt1/plt2. Overexpression of PLT2greatly rescues the root meristem defeciency in abo8, with or without ABA treatment. These genetic data show that ABA and ROS both inhibit root meristem activity by down regulating the PLT expression. In summary, our results indicate that ABA-mediated ROS signaling may regulates root growth and development by controlling auxin accumulation/signaling and PLT expression-mediated modulation of root meristem activity in Arabidopsis.更多还原