Cloning of cDNAs for genes that are early-responsive to dehydration stress (ERDs) inArabidopsis thaliana L.: identification of three ERDs as HSP cognate genes

InArabidopsis thaliana L., accumulation of abscisic acid (ABA) began to increase 2 h after plants had been subjected to dehydration stress and reached maximum levels after 10h. Differential hybridization was used to isolate 26Arabidopsis cDNAs with gene expression induced by a 1 h dehydration treatment. The cDNA clones were classified into 16 groups based on Southern blot hybridization, and named ERD (early-responsive todehydration) clones. Partial sequencing of the cDNA clones revealed that three ERDs were identical to those of HSP cognates (Athsp70-1, Athsp81-2, and ubiquitin extension protein). Dehydration stress strongly induced the expression of genes for the three ERDs, while application of ABA, which is known to act as a signal transmitter in dehydration-stressed plants, did not significantly affect the ERD gene expression. This result suggests that these HSP cognates are preferentially responsive to dehydration stress inA. thaliana, and that signaling pathways for the expression of these genes under conditions of dehydration stress are not mainly mediated by ABA. We also discuss the possible functions of these three ERD gene products against dehydration stress.     

蒙古沙冬青AmRD22基因的克隆及耐逆功能研究

脱水应答蛋白22(RD22)属于植物特有的BURP蛋白家族中的一个亚族,与耐逆性关系密切。该研究从中国西北荒漠区特有的强耐逆植物蒙古沙冬青克隆到一个RD22基因(AmRD22)的全长cDNA,并对其编码蛋白、表达模式和耐逆功能进行了研究。结果表明：(1)AmRD22蛋白(360 aa)的初级结构中含有RD22亚族共有的4个结构域,预测其定位于细胞壁;在功能已知的RD22蛋白中,AmRD22与大豆GmRD22的进化关系最近。(2)在室内培养的蒙古沙冬青幼苗中,AmRD22的表达受失水、高盐、低温和ABA胁迫的诱导显著上调,其中失水和低温胁迫诱导其上调幅度较大;在野外生长的蒙古沙冬青植株嫩叶中,其表达量从中秋至隆冬远高于其他季节。(3)转AmRD22基因拟南芥的耐盐性显著提高且Na⁺含量降低,其耐旱性也有较明显的改善且在种子萌发早期对外源ABA的敏感性降低,但耐冷性和耐冻性无明显变化。     

从水分胁迫的识别到ABA积累的细胞信号转导

由于植物在生长和发育过程中不可避免地要遭受各种环境胁迫的影响,植物只有通过对环境胁迫的快速感知和主动反应才得以生存和发展.植物这种对环境胁迫的快速感知和主动反应体现在环境胁迫下植物可以通过一系列基因的表达调控来实现各种抗逆的生理生化反应.虽然得以鉴定的水分胁迫应答基因越来越多,但其中只有极少的基因在抗逆中的基本功能已得到初步认识.从细胞对水分胁迫原初信号的感知到基因表达调控包括了一系列复杂的细胞逆境信息传递过程.脱落酸(abscisic acid, ABA)作为重要的细胞逆境信号物质介导了一系列基因表达,因此从细胞对水分胁迫原初信号的感知到编码ABA生物合成关键酶基因的表达是一条最为关键的细胞逆境信息传递途径.逆境应答基因功能的鉴定以及对整个细胞信号传递过程中详尽的分子机制的了解无疑是今后最有趣的也是最为重要的研究课题.     

The Arabidopsis tandem zinc finger protein AtTZF1 affects ABA- and GA-mediated growth, stress and gene expression responses

Tandem zinc finger (TZF) proteins are characterized by two zinc-binding CCCH motifs arranged in tandem. Human TZFs such as tristetraproline (TTP) bind to and trigger the degradation of mRNAs encoding cytokines and various regulators. Although the molecular functions of plant TZFs are unknown, recent genetic studies have revealed roles in hormone-mediated growth and environmental responses, as well as in the regulation of gene expression. Here we show that expression of AtTZF1 (AtCTH/AtC3H23) mRNA is repressed by a hexokinase-dependent sugar signaling pathway. However, AtTZF1 acts as a positive regulator of ABA/sugar responses and a negative regulator of GA responses, at least in part by modulating gene expression. RNAi of AtTZF1-3 caused early germination and slightly stress-sensitive phenotypes, whereas plants over-expressing AtTZF1 were compact, late flowering and stress-tolerant. The developmental phenotypes of plants over-expressing AtTZF1 were only partially rescued by exogenous application of GA, implying a reduction in the GA response or defects in other mechanisms. Likewise, the enhanced cold and drought tolerance of plants over-expressing AtTZF1 were not associated with increased ABA accumulation, suggesting that it is mainly ABA responses that are affected. Consistent with this notion, microarray analysis showed that over-expression of AtTZF1 mimics the effects of ABA or GA deficiency on gene expression. Notably, a gene network centered on a GA-inducible and ABA/sugar-repressible putative peptide hormone encoded by GASA6 was severely repressed by AtTZF1 over-expression. Hence AtTZF1 may serve as a regulator connecting sugar, ABA, GA and peptide hormone responses.     

转CkLEA4基因拟南芥种子萌发期的抗逆性分析

该研究在实验室前期研究的基础上,将受脱水、盐胁迫和ABA诱导的柠条锦鸡儿CkLEA4基因转入野生型拟南芥,并利用实时荧光定量PCR从8株纯合体中筛选出3个表达量不同的株系,比较野生型和转CkLEA4基因过表达拟南芥种子在不同胁迫处理下的萌发率,以探讨CkLEA4基因在植物抵抗逆境胁迫中的功能。结果发现:(1)在不同浓度NaCl、甘露醇及ABA处理下,转CkLEA4基因过表达拟南芥种子的萌发率均高于野生型,随着NaCl、甘露醇及ABA浓度增加,各株系萌发率均降低,但野生型的萌发率下降幅度均高于3个过表达株系,并且在200mmol/L NaCl和400mmol/L甘露醇处理下,过表达株系子叶绿化率均显著高于野生型。(2)在低浓度ABA处理下,CkLEA4过表达植株子叶的绿化率也高于野生型。研究表明,柠条锦鸡儿CkLEA4基因提高了拟南芥种子萌发阶段对盐、ABA及渗透胁迫的耐受性。     

Knockout of AtDjB1, a J‐domain protein from Arabidopsis thaliana,alters plant responses to osmotic stress and abscisic acid

AtDjB1 is a member of the Arabidopsis thaliana J‐protein family. AtDjB1 is targeted to the mitochondria and plays a crucial role in A. thaliana heat and oxidative stress resistance. Herein, the role of AtDjB1 in adapting to saline and drought stress was studied in A. thaliana. AtDjB1 expression was induced through salinity, dehydration and abscisic acid (ABA) in young seedlings. Reverse genetic analyses indicate that AtDjB1 is a negative regulator in plant osmotic stress tolerance. Further, AtDjB1 knockout mutant plants (atj1‐1) exhibited greater ABA sensitivity compared with the wild‐type (WT) plants and the mutant lines with a rescued AtDjB1 gene. AtDjB1 gene knockout also altered the expression of several ABA‐responsive genes, which suggests that AtDjB1 is involved in osmotic stress tolerance through its effects on ABA signaling pathways. Moreover, atj1‐1 plants exhibited higher glucose levels and greater glucose sensitivity in the post‐germination development stage. Applying glucose promoted an ABA response in seedlings, and the promotion was more evident in atj1‐1 than WT seedlings. Taken together, higher glucose levels in atj1‐1 plants are likely responsible for the greater ABA sensitivity and increased osmotic stress tolerance.     

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。     

A Putative PP2C-Encoding Gene Negatively Regulates ABA Signaling in Populus euphratica

A PP2C homolog gene was cloned from the drought-treated cDNA library of Populus euphratica. Multiple sequence alignment analysis suggested that the gene is a potential ortholog of HAB1. The expression of this HAB1 ortholog (PeHAB1) was markedly induced by drought and moderately induced by ABA. To characterize its function in ABA signaling, we generated transgenic Arabidopsis thaliana plants overexpressing this gene. Transgenic lines exhibited reduced responses to exogenous ABA and reduced tolerance to drought compared to wide-type lines. Yeast two-hybrid analyses indicated that PeHAB1 could interact with the ABA receptor PYL4 in an ABA-independent manner. Taken together; these results indicated that PeHAB1 is a new negative regulator of ABA responses in poplar.     

丹参抗性基因SmORA1的克隆及诱导表达分析

该研究采用PCR方法从丹参中克隆出一条乙烯应答因子结合蛋白(ERF)转录因子编码基因,命名为SmORA1,GenBank登录号为KT359598。经分析发现该基因全长648bp,不包含内含子,编码206个氨基酸残基。编码蛋白SmORA1含有典型的AP2结合结构域。表达分析结果表明,SmORA1主要在丹参根中表达,且该基因的表达明显受到茉莉酸甲酯(MeJA)、脱落酸(ABA)、乙烯(ET)、机械创伤和病原菌等逆境信号的诱导,但低温和脱水情况下SmORA1表达下调。研究表明,SmORA1参与丹参生物胁迫反应,可整合JA、ABA、ET和病原菌等胁迫信号途径。