Transgenic approaches to increase dehydration-stress tolerance in plants

Plant productivity is strongly influenced by abiotic stress conditions induced by drought, high salt and low temperature. Plants respond to these conditions with an array of biochemical and physiological adaptations, at least some of which are the result of changes in gene expression. Transgenic approaches offer a powerful means of gaining valuable information to better understand the mechanisms governing stress tolerance. They also offer new opportunities to improve dehydration-stress tolerance in crops by incorporating a gene involved in stress protection into species that lack them. In this review, we discuss progress made towards understanding the molecular elements involved in dehydration-stress responses that have been used to improve salt or drought tolerance following several transgenic approaches. Further, we discuss various strategies being used to produce transgenic plants with increased tolerance to dehydration stress. These include the overproduction of enzymes responsible for biosynthesis of osmolytes, late-embryogenesis-abundant proteins and detoxification enzymes. At this time, there is a need for a careful appraisal of the genes to be selected and promoter elements to be used, because constitutive expression of these genes may not be desirable in all applications. In this context, the advantages and limitations of transgenic approaches currently being used are discussed together with the importance of using stress-inducible promoters and the introduction of multiple genes for the improvement of dehydration-stress tolerance.     

Over-expression of OSRIP18 increases drought and salt tolerance in transgenic rice plants

Both drought and high salinity stresses are major abiotic factors that limit the yield of agricultural crops. Transgenic techniques have been regarded as effective ways to improve crops in their tolerance to these abiotic stresses. Functional characterization of genes is the prerequisite to identify candidates for such improvement. Here, we have investigated the biological functions of an Oryza sativa Ribosome-inactivating protein gene 18 (OSRIP18) by ectopically expressing this gene under the control of CaMV 35S promoter in the rice genome. We have generated 11 independent transgenic rice plants and all of them showed significantly increased tolerance to drought and high salinity stresses. Global gene expression changes by Microarray analysis showed that more than 100 probe sets were detected with up-regulated expression abundance while signals from only three probe sets were down-regulated after over-expression of OSRIP18. Most of them were not regulated by drought or high salinity stresses. Our data suggested that the increased tolerance to these abiotic stresses in transgenic plants might be due to up-regulation of some stress-dependent/independent genes and OSRIP18 may be potentially useful in further improving plant tolerance to various abiotic stresses by over-expression.     

拟南芥非生物胁迫应答基因表达的调节子研究概况

分子生物学研究表明,植物中由诸如干旱、高盐和低温等环境胁迫因子诱导的几个基因具有多种功能。大多数干旱应答基因是由植物激素脱落酸（ABA）诱导的,但也有少数基因例外。对模式植物拟南芥基因表达中的干旱应答基因的分析表明,至少存在4个独立调节系统（调节子）。对典型胁迫诱导表达的一些基因中启动子的顺势作用元件和影响这些基因表达的转录子也已进行了分析。已经分离出与脱水效应元件/C重复序列（DRE/CRT）顺势作用元件结合的转录因子,并命名为DRE结合蛋白1/C重复序列结合因子（DREB1/CBF）和DRE结合蛋白2（DREB2）。在转基因拟南芥植株中,DREB1/CBF过量表达可增加其抗寒、抗旱和抗盐碱的能力。DREB1/CBF基因已成功地在许多不同作物中得到应用,从而提高作物对非生物胁迫的耐受性。与胁迫反应相关的其他转录因子的研究也正在取得进展。     

Two different novel cis-acting elements of erd1, a clpA homologous Arabidopsis gene function in induction by dehydration stress and dark-induced senescence

Many plant genes have been shown to be induced by water stress and function in stress tolerance. The erd1 gene has been shown to be upregulated in response to both water stress and etiolation. Promoter studies using the erd1 promoter region fused to the luciferase (LUC) reporter gene in Arabidopsis thaliana were performed to identify the putative cis elements involved. Results indicated that the cis elements, responsible for gene expression during dehydration and etiolation, are separately located in two discrete portions of the erd1 promoter. Base substitution analysis showed that a 14-bp region from -599 to -586, and a myc recognition motif from -466 to -461 are necessary for the induction of LUC activity in dehydrated plants. On the other hand, base substitution analysis revealed that both an abscisic acid responsive element (ABRE)-like sequence (from -199 to -195) and an ACGT sequence (from -155 to -152) are required for an etiolation-induced increase in LUC activity. LUC activity measurements from etiolated transgenic plants incubated in either water, N6-benzyleadenine (BA), or a 1% sucrose solution found that while BA was able to delay the increase in LUC activity seen in water-treated plants, no increase in LUC activity was seen in plants incubated in sucrose. These results indicate that the erd1 promoter contains two different regulatory systems that are involved in upregulation by dehydration stress and dark-induced senescence.     

干旱胁迫诱导下植物基因的表达与调控

干旱胁迫能够诱导植物表达大量的基因 ,研究这些基因的表达与调控 ,为植物抗旱的定向育种创造条件。本文系统介绍了在干旱胁迫条件下 ,植物体内渗透调节物质和可溶性糖合成有关的基因、离子和水分通道及Lea蛋白基因的表达 ,以及与这些基因表达相关的调控元件和因子 ,干旱胁迫信号转导等方面的最新研究进展。     

Transgenic tobacco expressing a ring domain-containing protein of<Emphasis Type="Italic">Capsicum annuum</Emphasis> confers improved cold tolerance

Zinc finger proteins function in plant tolerances to stresses from cold, dehydration, and salt. To determine the mechanisms for those underlying defenses, we previously used cDNA microarrays and northern blot analysis to identify a gene for the ring zinc finger protein (RDCP1) from hot pepper (Capsicum annuum). In that study, we showed that theRDCP1 gene was strongly induced by cold stress and, to a lesser degree, by ABA and high salt Here, we have used a Ti-plasmid andAgrobacterium- mediated transformation to engineerRDCP1 under the control of the CaMV35S promoter for constitutive expression in tobacco. The resultant RDCP1 transgenic plants exhibit significantly increased tolerance to low temperatures. Moreover, some of those transgenics have greater drought tolerance. In addition, none of the RDCP1 transgenic plants show any visible alterations from the wild phenotype. These current results demonstrate the biological role of RDCP1 in conferring stress tolerance.