CBF:平衡植物低温应答与生长发育的关键

低温是影响植物生长发育以及植被分布的重要环境因子。目前,低温信号研究中比较清楚的是CBF依赖的低温信号途径。该文总结了近年来有关CBF的研究成果,详细介绍了CBF家族成员在植物耐寒性中的重要作用,着重分析与讨论CBF介导的低温调控网络及一系列复杂调控机制。理解CBF的复杂作用机制有助于了解植物中CBF介导的冷信号如何平衡耐寒性与生长发育,进而有助于耐寒作物的培育。     

低温条件下中国野生拟南芥种群中CBF3与ROS浓度的相关性

活性氧(ROS)是植物光合作用和呼吸作用的副产物,环境胁迫可加速植物体内ROS的产生,造成植物细胞膜的过氧化,同时给光反应中心II带来光伤害。RFOs是植物体内的1类寡聚糖家族,其对环境胁迫的响应很可能与清除过剩的ROS相关。前期的研究显示,由于中国长江流域野生拟南芥(Arabidopsis thaliana)种群中CBF3基因的变异,种群的冰冻耐受性和体内RFOs含量的积累普遍低于Col生态型。研究表明,长江流域种群中ROS代谢通路在低温处理后的表达与Col生态型相比发生了明显的分化,并且植物体内ROS的浓度增高;而将Col生态型中能正常响应环境冷信号的CBF3基因转入长江流域种群后,转基因植株的冰冻耐受性得到显著提高,体内RFOs积累亦增加,而ROS浓度显著降低。这些结果说明,低温条件下CBF3很可能通过直接调控植物体内RFOs的生物积累来参与调控下游过剩ROS的清除过程。中国长江流域野生拟南芥种群低温条件下体内ROS浓度的升高,很可能是由于种群中CBF3基因发生了自然变异从而丧失了冷响应能力造成的。     

中国樱桃CBF/DREB转录因子PpcCBF的克隆与表达分析

低温诱导中国樱桃(Prunus pseudocerasus)花芽休眠解除是一个非常复杂的过程。研究花芽响应低温的分子生物学机制将是揭示这一问题的关键。CBF/DREB转录因子在植物低温响应过程中发挥着重要作用。为此,本研究从"短柄"樱桃中克隆了一个CBF/DREB转录因子,命名为PpcC BF。生物信息学分析表明,Ppc CBF基因的开放阅读框为720 bp,编码239个氨基酸。Ppc CBF具有典型的CBF/DREB转录因子的结构特征,AP2结合域高度保守,聚类分析发现李属植物CBF/DREB转录因子亲缘关系较近。实时定量表达分析发现,Ppc CBF受低温诱导表达,且不依赖ABA。在花芽休眠解除过程中,随着低温积累而表达上调,休眠解除临界期之后下调表达,与花芽休眠解除具有极大相关性。     

& 转录因子CBF在植物抗寒中的重要作用

低温能够诱导植物许多基因的表达,从而使植物具有抗寒性,这种现象称为冷驯化。对于植物冷驯化的分子机理,目前研究的最多的是CBF转录因子调控的信号转导途径,其作用途径可归纳为：CBF(C-repeat Binding Factor)转录因子→CRT/DRE(C-repeat /Dehydration Responsive Element)基序→COR基因表达→植物抗寒性增加。研究CBF转录因子在抗寒中的作用机制,能为提高植物的抗寒性,培育抗寒作物品种提供新方向。      

拟南芥冷诱导型启动子CBF 3的克隆及活性检测

目的：构建冷诱导型启动子CBF3基因的植物表达载体,并将其转入烟草。方法：以拟南芥基因组DNA为模板,通过特异PCR扩增,克隆冷诱导表达启动子CBF3（C-repeat binding factor）。用CBF3启动子替换pBI121载体上的35S启动子构建新的载体pBC-GUS,通过农杆菌介导的叶盘法转化烟草。结果：获得了转基因烟草,转基因烟草的GUS组织化学染色及PCR分析结果表明,在低温诱导下,CBF3启动子可增强GUS基因表达。结论：CBF3启动子可应用于植物抗冷基因工程研究。     

植物响应低温胁迫的分子机制研究

低温是限制植物生长发育以及植被分布的重要环境因子。目前,低温信号途径研究的比较清楚的是CBF(C-repeat(CRT)-binding factors)依赖的信号途径。研究表明,植物激素也参与了植物的低温响应。现将根据当前的研究进展总结植物响应低温的分子机制以及植物激素信号与低温信号的交互作用。     

拟南芥CBF/DREB途径的研究进展及其在植物基因工程中的应用

细胞膜感知低温环境信号,通过信号转导激活以CBF/DREB信号途径为主、兼与其他途径交谈和交叠所构成的信号网络,继而调控下游相应功能蛋白的表达,赋予植物低温抗性。文章重点介绍了拟南芥CBF/DREB信号传导途径的研究进展、CBF基因在高等植物中的保守性,以及构建CBF转基因抗冻植物所取得的成果,包括CBF的表达调控与作用的分子机制、影响CBF途径的一些重要蛋白和环境因子、组成性启动子以及冷诱导特异性启动子驱动CBF基因表达所获得的抗冻转基因植物的研究进展。同时,对该研究领域未来可能的发展方向进行了展望。     

植物冷响应基因调控和冷信号转导

植物细胞内存在丰富多样的冷响应基因,但只有一部分与植物的抗冷性有关.植物抗冷性状是由多基因调控的累积性状,CBF(CRT-DRE binding factors)是许多抗冷基因的转录激活子;Ca2 与蛋白质的磷酸化和去磷酸化反应参与了冷信号转导;最近分子方面的的证据也表明在植物细胞内存在着冷信号转导的负调控元件.     

Role for dopamine in malonate-induced damage in vivo in striatum and in vitro in mesencephalic cultures

Defects in mitochondrial energy metabolism have been implicated in the pathology of several neurodegenerative disorders. In addition, the reactive metabolites generated from the metabolism and oxidation of the neurotransmitter dopamine (DA) are thought to contribute to the damage to neurons of the basal ganglia. We have previously demonstrated that infusions of the metabolic inhibitor malonate into the striata of mice or rats produce degeneration of DA nerve terminals. In the present studies, we demonstrate that an intrastriatal infusion of malonate induces a substantial increase in DA efflux in awake, behaving mice as measured by in vivo microdialysis. Furthermore, pretreatment of mice with tetrabenazine (TBZ) or the TBZ analogue Ro 4-1284 (Ro-4), compounds that reversibly inhibit the vesicular storage of DA, attenuates the malonate-induced DA efflux as well as the damage to DA nerve terminals. Consistent with these findings, the damage to both DA and GABA neurons in mesencephalic cultures by malonate exposure was attenuated by pretreatment with TBZ or Ro-4. Treatment with these compounds did not affect the formation of free radicals or the inhibition of oxidative phosphorylation resulting from malonate exposure alone. Our data suggest that DA plays an important role in the neurotoxicity produced by malonate. These findings provide direct evidence that inhibition of succinate dehydrogenase causes an increase in extracellular DA levels and indicate that bioenergetic defects may contribute to the pathogenesis of chronic neurodegenerative diseases through a mechanism involving DA.     

Changes in lactate dehydrogenase activity in chicken tissues in hyperthyreosis in ontogenesis

The lactate dehydrogenase activity in reactions of lactate oxidation and synthesis was studied in subfractions of the chicken brain, heart and liver at the embryonal, early postembryonal and adult stages of development after thyroxine administration. It has been shown that during embryogenesis thyroxine predominantly enhanced the rate of lactate oxidation in the mitochondrial tissues. A marked increase in the lactate synthesis was found in cytoplasm of the adult chicken tissues. Specificity of enzyme activity alterations was detected in the chicken brain during ontogenesis after thyroxine administration.     

Scurvy in capybaras bred in captivity in Argentine

In order to determine if the absence of vitamin C in the diet of capybaras (Hydrochoerus hydrochaeris) causes scurvy, a group of seven young individuals were fed food pellets without ascorbic acid, while another group of eight individuals received the same food with 1 g of ascorbic acid per animal per day. Animals in the first group developed signs of scurvy-like gingivitis, breaking of the incisors and death of one animal. Clinical signs appeared between 25 and 104 days from the beginning of the trial in all individuals. Growth rates of individuals deprived of vitamin C was considerably less than those observed in the control group. Deficiency of ascorbic acid had a severe effect on reproduction of another population of captive capybaras. We found that the decrease in ascorbic acid content in the diet affected pregnancy, especially during the first stages. The results obtained suggest that it is necessary to supply a suitable quantity of vitamin C in the diet of this species in captivity.     

SSTR5 ablation in islet results in alterations in glucose homeostasis in mice

Somatostatin (SST) peptide is a potent inhibitor of insulin secretion and its effect is mediated via somatostatin receptor 5 (SSTR5) in the endocrine pancreas. To investigate the consequences of gene ablation of SSTR5 in the mouse pancreas, we have generated a mouse model in which the SSTR5 gene was specifically knocked down in the pancreatic beta cells (betaSSTR5Kd) using the Cre-lox system. Immunohistochemistry analysis showed that SSTR5 gene expression was absent in beta cells at three months of age. At the time of gene ablation, betaSSTR5Kd mice demonstrated glucose intolerance with lack of insulin response and significantly reduced serum insulin levels. Insulin tolerance test demonstrated a significant increase of insulin clearance in vivo at the same age. In vitro studies demonstrated an absence of response to SST-28 stimulation in the betaSSTR5Kd mouse islet, which was associated with a significantly reduced SST expression level in betaSSTR5Kd mice pancreata. In addition, betaSSTR5Kd mice had significantly reduced serum glucose levels and increased serum insulin levels at 12 months of age. Glucose tolerance test at an older age also indicated a persistently higher insulin level in betaSSTR5Kd mice. Further studies of betaSSTR5Kd mice had revealed elevated serum C-peptide levels at both 3 and 12 months of age, suggesting that these mice are capable of producing and releasing insulin to the periphery. These results support the hypothesis that SSTR5 plays a pivotal role in the regulation of insulin secretion in the mouse pancreas.