How Plants Cope with Cadmium: Staking All on Metabolism and Gene Expression

Environmental pollullon is one of the major problems for human health. Toxic heavy metals are normally present as soil constituents or can also be spread out in the environment by human activity and agricultural techniques. Soil contamination by heavy metals as cadmium, highlights two main aspects: on one side they interfere with the life cycle of plants and therefore reduce crop yields, and on the other hand, once adsorbed and accumulated into the plant tissues, they enter the food chain poisoning animals and humans. Considering this point of view, understanding the mechanism by which plants handle heavy metal exposure, In particular cadmium stress, is a primary goal of plant-blotechnology research or plant breeders whose aim is to create plants that are able to recover high amounts of heavy metals, which can be used for phytoremediation, or identify crop varieties that do not accumulate toxic metal in grains or fruits. In this review we focus on the main symptoms of cadmium toxicity both on root apparatus and shoots. We elucidate the mechanisms that plants activate to prevent absorption or to detoxify toxic metal ions, such as synthesis of phytochelatins, metallothioneins and enzymes involved in stress response. Finally we consider new plant-biotechnology applications that can be applied for phytoremediation.     

How Plants Cope with Water Stress in the Field? Photosynthesis and Growth

Plants are often subjected to periods of soil and atmosphericwater deficit during their life cycle. The frequency of suchphenomena is likely to increase in the future even outside today’sarid/semi-arid regions. Plant responses to water scarcity arecomplex, involving deleterious and/or adaptive changes, andunder field conditions these responses can be synergisticallyor antagonistically modified by the superimposition of otherstresses. This complexity is illustrated using examples of woodyand herbaceous species mostly from Mediterranean-type ecosystems,with strategies ranging from drought-avoidance, as in winter/springannuals or in deep-rooted perennials, to the stress resistanceof sclerophylls. Differences among species that can be tracedto different capacities for water acquisition, rather than todifferences in metabolism at a given water status, are described.Changes in the root : shoot ratio or the temporaryaccumulation of reserves in the stem are accompanied by alterationsin nitrogen and carbon metabolism, the fine regulation of whichis still largely unknown. At the leaf level, the dissipationof excitation energy through processes other than photosyntheticC-metabolism is an important defence mechanism under conditionsof water stress and is accompanied by down-regulation of photochemistryand, in the longer term, of carbon metabolism.     

植物缺氧响应相关基因的表达调控机制

对近年来缺氧应答相关基因的分离、克隆及缺氧响应信号转导模式与调控机制作了综述。分析了缺氧应答基因的序列特点,概述了植物感受缺氧胁迫的信号传递模式,阐述了缺氧响应的调控机制并着重讨论了调控因子AtMYB2的调控特点,并对缺氧相关研究进行了展望。     

与植物镉吸收转运相关的主要基因家族

镉(cadmium)是一种对植物毒性极强的非必需微量元素,影响植物生长发育,甚至死亡,并可在植物体内积累而威胁食物链顶端生物的生命健康。目前已发现有多类基因家族的成员参与了植物中镉的吸收转运过程,包括P型ATP酶、ABC、MATE、NRAMP、CE、CAX、ZIP、OPT等。这些基因家族主要是在吸收转运铁、锌、镁等植物必需微量元素的同时,也具有吸收转运镉等有毒重金属的功能。     

Regulation of Gene Expression in Higher Plants

The study on regulation of gene expression in higher plants has attracted attention of many scientists and is also one of the major scientific research areas in modern biological studies. With advancement of the technology of genetic engineering, more and more details of gene regulation are revealed and it has been found that regulatory zones of most genes are located at the 5' upstream promoter regions. Now,the study on regulation of gene expression is mainly focused on light regulated genes, tissue specific genes, environmental stress induced genes, bormone-induced genes and so on. This article gives a more or less comprehensive review on the several aspects mentioned above.     

肿瘤中甲硫氨酸代谢及其相关基因的表达调控

甲硫氨酸(methionine)作为人体必需氨基酸,生理功能多样,在肿瘤代谢重编程过程中具有重要意义。研究发现,多种肿瘤细胞对外源性甲硫氨酸存在依赖性,该效应被称为Hoffman效应。在人体内,甲硫氨酸经甲硫氨酸循环代谢,参与一碳单位代谢、叶酸循环,以及多胺、谷胱甘肽、半胱氨酸和核苷酸等多种物质的合成。肿瘤中常出现甲硫氨酸代谢的改变,并伴随甲硫氨酸代谢相关酶基因表达的异常,其中以甲硫氨酸腺苷转移酶(methionine adenosyltransferase, MAT)相关基因表达改变及甲硫腺苷磷酸化酶(methylthioadenosine phosphorylase,MTAP)基因的缺失最为常见,二者可分别引起甲硫氨酸循环及甲硫氨酸补救合成途径的异常,进而导致甲基供体S-腺苷甲硫氨酸(S-adenosylmethionine, SAM)的生成减少和甲硫腺苷(methylthioadenosine, MTA)的堆积,其与肿瘤的发生、发展和转移等活动密切相关。由甲硫氨酸的代谢改变和代谢酶的基因表达异常,分别衍生出2种不同的治疗策略,即甲硫氨酸限制疗法和靶向治疗。本文将从甲硫氨酸代谢出发,阐述肿瘤中甲硫氨酸依懒性、肿瘤细胞MAT和MTAP相关基因的表达调控,并概述甲硫氨酸相关肿瘤治疗方案的新进展与新问题,为肿瘤治疗方案的进一步探索提供新思路。     

染色质可及性与植物基因表达调控

真核生物基因组上的核小体呈现不均匀分布, 转录活跃区域的染色质结构相对松散且易被调节蛋白结合, 这些区域的可接近程度称为染色质可及性。随着测序技术的发展, DNase-seq、ATAC-seq、MNase-seq和NOMe-seq等组学技术的应用, 全基因组范围内染色质可及性检测变得简便且高效。该文主要介绍了真核生物染色质可及性的4种基本检测方法的技术原理, 总结了核小体定位、组蛋白修饰以及转录因子结合与染色质可及性的关系, 并综述了染色质可及性参与植物生长发育和环境响应研究进展, 以期为植物领域全基因组水平染色质可及性研究、顺式调控元件挖掘及发育和环境响应过程中基因表达调控网络的解析提供借鉴。     

多倍体植物中基因表达模式的变化

植物杂交和多倍化能导致基因组结构发生变化,并显著影响了基因表达,因此认为杂交和多倍化是促进植物进化的一个重要力量。近些年大量的研究表明植物多倍化后基因表达模式发生了复杂的改变,包括基因沉默、基因表达的基因组偏向性及组织特异性、基因激活等现象,本文对这些现象及其特点和机制进行了综述。