香蕉MaASR1基因通过ABA途径提高拟南芥抗旱性的作用机制

香蕉MaASR1基因在植物响应逆境胁迫时发挥着重要作用,为了进一步研究MaASR1基因转入拟南芥后增强其抗旱性的分子机制,运用DNA芯片技术来筛选野生型的拟南芥和转MaASR1基因的拟南芥在不做任何处理和干旱胁迫处理条件下的差异基因。对基因芯片中与ABA途径相关的上调和下调大于2倍的差异基因进行了荧光定量PCR的验证,实验结果发现在以上两种处理条件下,转MaASR1基因的拟南芥体内ABA的生物合成量比野生型拟南芥低,而ABA的降解量却升高。当受到干旱胁迫时,转基因拟南芥体内ABI5和ABF1基因的表达量会得到提高,而ABI5基因可以赋予转基因拟南芥株系耐旱性和抗旱性的功能是因为LEA类的蛋白被其调控表达和提高了ABA诱导基因的表达水平。ABF1基因发挥其提高转基因株系抗旱性的功能则可以通过参与ABA信号途径以及与其它的ABI类基因共同作用来实现。除此之外转基因拟南芥株系抗旱性的提高,与CBL/CIPK复合物参与的胁迫应答途径无关。以上结果为解析MaASR1基因作为转录因子通过ABA途径提高植物抗旱能力的分子机制奠定基础。     

玉米ZmCIPK24-2基因在盐胁迫应答中的功能研究

土壤盐化会影响作物正常生长发育,导致农作物减产。植物在长期适应环境的过程中,进化出了相应的耐盐分子机制。钙调磷酸酶B类蛋白(CBL)及CBL互作蛋白激酶(CIPK)参与植物对盐胁迫的响应。本研究鉴定到一个拟南芥AtSOS2的同源基因ZmCIPK24-2,实时荧光定量聚合酶链式反应结果表明ZmCIPK24-2基因在玉米各组织部位广泛表达,其中在花粉表达量最高;ZmCIPK24-2受盐胁迫诱导表达。ZmCIPK24-2能部分互补拟南芥atsos2突变体的盐敏感表型,在高盐浓度下转基因株系比atsos2突变体的存活率显著提高,根长显著增长。亚细胞定位实验表明ZmCIPK24-2定位于细胞质、细胞膜与核膜。利用酵母双杂交实验及LUC互补成像实验发现ZmCIPK24-2与玉米CBLs家族中的ZmCBL1、ZmCBL4、ZmCBL8和ZmCBL9互作。本研究为解析玉米CBL-CIPK信号通路的功能提供了新的实验证据。     

质膜内在蛋白ZmPIP1;1参与玉米耐旱性和光合作用的功能分析

质膜内在蛋白(plasma membrane intrinsic proteins,PIPs)是水通道蛋白主要亚家族成员之一,在植物生长发育过程中具有重要调节功能。前期研究表明,玉米ZmPIP1;1基因表达受到渗透和盐胁迫的强烈诱导,但其在玉米中的生物学功能尚不明确。本研究通过玉米遗传转化获得了ZmPIP1;1超表达转基因株系,干旱胁迫实验揭示了ZmPIP1;1超表达转基因株系较野生型具有较低的水分散失率及较强的干旱胁迫耐性。转录组测序结果表明参与ABA生物合成及其信号通路相关基因的表达水平发生了显著变化。在田间正常生长条件下,ZmPIP1;1超表达转基因植株与野生型在生长发育过程中没有明显差异,但转基因玉米株系具有较高的光合效率,粒宽和百粒重增加,玉米单果穗的产量提高。此外,通过荧光双分子互补实验观察到ZmPIP1;1和ZmPIP2;6蛋白在玉米叶肉细胞原生质体的细胞质膜和叶绿体膜上存在互作,并且可能导致了ZmPIP蛋白的重定位。该研究为ZmPIP1;1分子机制的解析奠定了重要基础,为玉米高光效分子设计育种开辟了新的途径。     

玉米小分子热激蛋白ZmHSP17.7基因的克隆与功能分析

植物热激蛋白是一类代表性高温响应蛋白。以玉米种质POB21为材料,克隆了一个CDS序列长度为477 bp的小分子热激蛋白基因。该基因编码的蛋白含158个氨基酸,具有HSP20蛋白典型的ACD结构域,预测的等电点为5.36,分子量为17.746 k D,被命名为Zm HSP17.7。在水稻、拟南芥等植物基因组中都有其同源基因,进化和亚细胞定位分析表明,此基因属CI类小分子热激蛋白家族成员。Northern杂交分析表明,高温快速诱导Zm HSP17.7基因表达,15%PEG模拟干旱胁迫不诱导该基因表达,但在复合胁迫下干旱增强了高温的诱导效果。外源ABA也不影响该基因的表达。与野生型拟南芥相比,超表达Zm HSP17.7的转基因拟南芥在种子萌发和植株生长过程中表现出更强的高温和干旱耐受性,说明该基因可以在植物防御高温、干旱及复合胁迫中发挥一定作用。     

干旱胁迫下植物的信号转导及基因表达研究进展

干旱是影响植物生长的主要因素之一,研究植物在干旱胁迫下的反应机制具有重要的现实意义。ABA、H2O2和NO在植物响应干旱胁迫反应中可能作为信号分子的作用。在干旱胁迫下,植物由“渗透感受器”感受外界胁迫信号。通过第二信使及其下游蛋白激酶级联传导反应,调控了一系列基因的表达。根据干旱信号转导过程中胁迫相关基因的表达是否依赖ABA,存在依赖ABA和非依赖ABA两途径。综述了植物干旱胁迫信号的感知、传递及其诱导的基因表达调控等方面的研究进展,对植物抗旱性的分子机理进行了展望。     

拟南芥bZIP1转录因子通过与ABRE元件结合调节ABA信号传导

ABA作为一种重要的植物激素和生长调节剂,介导了高等植物在营养生长阶段对各种外界环境的响应和适应。bZIP类转录因子可以通过ABA依赖途径和ABA非依赖途径调节植物的生长发育和对非生物胁迫的耐性。本研究通过AtbZIP1 T-DNA插入突变的拟南芥植株ko-1 (SALK_059343)和ko-2 (SALK_069489C)在ABA处理后的表型实验,验证了AtbZIP1参与ABA依赖的信号传导通路。采用“三引物法”,分别在DNA水平和RNA水平通过PCR和RT-PCR验证了AtbZIP1基因在拟南芥突变体中的沉默效果。定量分析数据表明,在种子萌发阶段,经过0.6 μmol L^–1 ABA和0.8 μmol L^–1 ABA处理后,AtbZIP1缺失突变体拟南芥植株萌发率和叶片展开/绿色率比野生型植株高,在幼苗生长阶段,经过50 μmol L^–1 ABA处理后,AtbZIP1缺失突变体拟南芥植株根长比野生型植株长。为了确定AtbZIP1基因参与ABA信号传导是否依赖于ABRE元件,在大肠杆菌中表达了AtbZIP1 HIS6融合蛋白,并设计了核心序列为CACGTG的ABRE元件。凝胶阻滞电泳结果表明AtbZIP1融合蛋白可以与ABRE元件特异性结合。半定量RT-PCR分析表明,AtbZIP1基因的缺失改变了下游的ABA响应基因的表达。该结果表明AtbZIP1可以通过与ABRE元件结合调节植物对ABA处理的敏感性和下游ABA响应基因的表达,从而参与植物的ABA信号传导通路。     

ABA与植物耐盐信号转导途径的研究进展

盐胁迫是常见的非生物胁迫因素之一并严重地影响着植物的生长发育。简述了植物在应对盐胁迫时,在胁迫信号的感知、信号的转导和传递、胁迫诱导基因的表达等方面所形成的一系列适应性的分子机制,回顾了近年来对脱落酸信号转导和其受体的研究。分析表明脱落酸受体PYR/PYL/RCAR (pyrabatin resistance/like-pyrabatin resistance/regularly component of ABA receptors)的发现使得ABA的信号转导通路更为清楚,使ABA与植物耐盐胁迫的关系更加明确,认为ABA在植物耐盐信号转导途径中发挥了重要的作用,与经济作物的耐盐性密切相关。     

拟南芥G蛋白α亚基GPA1互作蛋白铜离子结合蛋白AtBCB的鉴定及功能分析

拟南芥G蛋白复合体(异源三聚体包括α、β、γ亚基)参与植物多个信号转导途径,G蛋白复合体通过膜上的G蛋白偶联受体(GPCR)接受胞外信号后通过3个亚基将信号传递给下游效应器。目前,有关植物G蛋白复合体的效应器及其信号传递途径的报道较少,寻找新的G蛋白的效应器有助于阐明G蛋白复合体相关的信号传导途径。本研究以拟南芥G蛋白α亚基GPA1为诱饵蛋白,利用泛素分离系统筛选拟南芥cDNA文库,获得一个与GPA1互作的铜离子结合蛋白AtBCB。荧光双分子杂交(BiFC)试验证明,GPA1与AtBCB的互作发生在细胞膜上。基因表达特性分析结果显示,GPA1和AtBCB受金属铝胁迫的诱导表达。进一步以野生型拟南芥(WT)、GPA1拟南芥突变体gpa1-4和AtBCB拟南芥突变体bcb为材料,研究该基因对植物耐金属铝胁迫的功能,结果显示,在无胁迫情况下,2个突变体和WT根部的丙二醛含量无显著差异;在100 µmol L^–1 Al³⁺处理下,gpa1-4突变体根部丙二醛含量显著(P<0.05)低于WT低;bcb根部丙二醛含量极显著(P<0.01)高于WT。对3个铝胁迫响应基因(苹果酸转运体基因AtALMT1、半类型ABC转运蛋白基因ALS1和ABC转运蛋白基因ALS3)的表达进行Real-time PCR分析,比较它们在突变体和野生型之间的表达差异,发现在有铝和无铝处理情况下,ALS1和ALS3的表达水平在突变体和WT间均无显著差异;在铝处理下,gpa1-4中AtALMT1的表达量极显著高于WT;在bcb中的表达量显著低于WT。以上结果表明,植物通过细胞膜上的G蛋白α亚基GPA1和铜离子结合蛋白AtBCB的相互作用调控下游基因AtALMT1的表达,参与植物对铝胁迫的响应,其中GPA1对铝胁迫耐受起负向作用,AtBCB对铝胁迫耐受起正向作用。     

黄瓜独脚金内酯信号转导基因CsMAX2的克隆与表达分析

独脚金内酯(strigolactone, SL)是一类新型植物激素,MAX2基因是独脚金内酯信号转导途径中的关键基因。本研究从黄瓜中克隆了CsMAX2基因,其编码715个氨基酸。生物信息学分析表明CsMAX2是一类亲水性蛋白,具有保守的F-box/LRR-repeat结构域,与南瓜中的MAX2基因亲缘关系最近,并且该蛋白与SL合成通路中的D27、CCD7与CCD8等蛋白均有互作关系。启动子分析表明该基因有多个响应非生物胁迫与激素应答的顺式作用元件。表达特性分析表明,CsMAX2在黄瓜的幼茎和幼叶中表达量较高;CsMAX2在黄瓜根与叶中积极响应干旱胁迫诱导上调表达;在盐胁迫条件下,Cs MAX2基因在根与叶中的表达量相反;同时发现CsMAX2也参与了ABA信号转导途径。本研究初步分析了Cs MAX2基因的蛋白特性及表达特性,为CsMAX2在黄瓜独脚金内酯信号转导途径中响应非生物胁迫提供了帮助。     

A note on the origin of Kalanchoë x vadensis Boom & Zeilinga (Crassulaceae)

Summary K x vadensis is a hybrid of K. blossfeldiana and K. marmorata obtained after doubling the number of chromosomes.     

Mechanisms and diversity of resistance to sorghum shoot fly,Atherigona soccata

Sorghum shoot fly, Atherigona soccata, is one of the important pests of postrainy season sorghums. Of the 90 sorghum genotypes evaluated for resistance to this pest, RHRB 12, ICSV 713, 25026, 93046 and 25027, IS 33844‐5, Giddi Maldandi and RVRT 3 exhibited resistance in postrainy season, while ICSB 463, Phule Anuradha, RHRB 19, Parbhani Moti, ICSV 705, PS 35805, IS 5480, 5622, 17726, 18368 and 34722, RVRT 1, ICSR 93031 and Dagidi Solapur showed resistance in rainy season, suggesting season‐specific expression of resistance to A. soccata. ICSB 461, ICSB 463, Phule Yasodha, M 35‐1, ICSV 700, 711, 25010, 25019 and 93089, IS 18662, Phule Vasudha, IS 18551 and 33844‐5 and Barsizoot had fewer deadhearts than plants with eggs across seasons, suggesting antibiosis as one of the resistance mechanism. Five genotypes exhibited resistance with high grain yield across seasons. Correlation, path and stepwise regression analyses indicated that leaf glossiness, seedling vigour, trichome density, oviposition and leaf sheath pigmentation were associated with the expression of resistance/susceptibility to shoot fly, and these can be used as marker traits to select and develop shoot fly‐resistant sorghums.     

Reaction of tritordeum to Fusarium culmorum and Septoria nodorum

Summary Hordeum chilense is a wild barley extensively used in wide crosses in the Triticeae. It could be a valuable source of resistance to Fusarium culmorum and Septoria nodorum. Some H. chilense x Triticum spp. amphiploids, named tritordeums, were more resistant than the parental wheat line to these diseases, others were not. Average contents of ergosterol and deoxynivalenol (DON) suggested that resistance to colonization by Fusarium was the highest for Hordeum chilense, followed by tritordeum and wheat in decreasing order. In particular, the H. chilense genotypes H7 and H17 enhanced the wheat resistance to F. culmorum in its tritordeum offsprings. Resistance to S. nodorum in tritordeum was not associated with tall plant height. There is sufficient genetic variation for resistance to F. culmorum and S. nodorum among tritordeum to allow the breeding of lines combining short straw and resistance to both diseases.     

Avoidance of leaf rust fungi in wild relatives of cultivated cereals

Summary Avoidance of rust fungi that was based on poor appressorium induction was previously found in Hordeum chilense. In the present study 95 accessions of Triticeae were screened for avoidance of Puccinia hordei. The percentage of appressorium formation per germinated spore ranged from 6 to 90%. On none of the 41 accessions of Aegilops, Agropyron, Elymus, Secale, Thinopyrum or Triticum studied was the rate of appressorium formation lower than 25%. Lower rates of appressorium formation were, however, found on accessions of wild barley species Hordeum brachyantherum, H. marinum, H. parodii and H. secalinum. Its implications in cereal breeding are discussed.     

Disease resistance in protected crops and mushrooms

Summary Cultivars of tomatoes, cucumbers, lettuce and peppers have been bred for resistance to one or more pathogens. Some tomato and cucumber cultivars have resistance to a wide range of diseases. Resistance has been transient in many cases and a succession of cultivars with new genes or new combinations of resistance genes has been necessary to maintain control. There has been a number of notable exceptions and these have included durable resistance to such pathogens asFulvia fulva and tomato mosaic virus. With lettuce the resistance situation is complicated by the occurrence of fungicide resistant pathotypes. There are no strains ofAgaricus bisporus purposely bred for disease resistance.In protected flower crops only resistance to Fusarium wilt in carnations has been purposely bred but differences in disease resistance are apparent in cultivars of many ornamental crops. This is particularly so in chrysanthemums where there are cultivars with resistance to many of the major pathogens. Similar situations occur with other flower crops and pot plants. Cultivars of some species have not been systematically investigated for resistance.The need for genetic resistance will increase with the further reduction, in the limits on pesticide use and an increasing public awareness and importance of pesticide pollution.ADAS is an executive agency of the Ministry of Agiculture, Fisheries and Food and the Welsh Office.     

Genetic constitution and diversity in four narrow endemic redwoods from the family Cupressaceae

The genetic constitution and diversity of four relictual redwoods are discussed in this review. These include monotypic genera of the family Cupressaceae: coast redwood (Sequoia sempervirens), giant sequoia (Sequoiadendron giganteum), dawn redwood (Metasequoia glyptostroboides), and alerce (Fitzroya cupressoides). All four species are narrow endemics, share a number of common phenotypic traits, including red wood, and are threatened species. Fossil history suggests that the ancestors of redwoods probably originated during the Cretaceous and Tertiary periods and flourished thereafter for millions of years. Towards the end of the Tertiary period began their decline and struggle for existence that continued during the subsequent geologic upheavals and climate changes, until the survival of the present-day redwoods in the current restricted locations in the world (USA, China, and South America). Although two species, Sequoiadendron and Metasequoia, are diploids (2n = 22), and the other two are polyploids: Fitzroya a tetraploid (2n = 4x = 44), and Sequoia a hexaploid (2n = 6x = 66); they all share the same basic chromosome number x = 11. The genome size in the hexaploid Sequoia is one of the largest (31,500 MB) in the conifers, while the genome sizes of diploid Metasequoia and Sequoiadendron are about one-third (~10,000 MB) of Sequoia. Genetic diversity in the redwoods is lower than most other gymnosperms, except in Sequoia, which seems to rank near the upper quarter of the coniferous forest trees. Genomic research is sparse in the redwoods, and should be pursued for a better understanding of their genome structure, function, and adaptive genetic diversity.     

Distribution,ecology and reproductive biology of wild tomatoes and related nightshades from the Atacama Desert region of northern Chile

Over the past 20 years, several expeditions were made to northern Chile to collect populations of wild tomatoes (Solanum chilense, S. peruvianum) and allied nightshades (S. lycopersicoides, S. sitiens), and obtain information about their geographic distribution, ecology and reproductive biology. Restricted mainly to drainages of the Andean and the coastal cordillera, populations are geographically fragmented. The two nightshade species are rare and threatened by human activities. Adaptation to extreme aridity and soil salinity are evident in S. chilense and S. sitiens (the latter exhibits several xerophytic traits not seen in the tomatoes) and to low temperatures in S. lycopersicoides and S. chilense. All tested accessions are self-incompatible, with the exception of one S. peruvianum population collected at the southern limit of its distribution. Several distinguishing reproductive traits—anther color, attachment, and dehiscence, pollen size, and flower scent—suggest S. sitiens and S. lycopersicoides attract different pollinators than S. chilense and S. peruvianum. The four Solanum spp. native or endemic to Chile provide a variety of novel traits which, through hybridization and introgression with cultivated tomato, could facilitate development of improved varieties, as well as research on a variety of basic topics, including plant-pollinator interactions, abiotic stress responses, and evolution of reproductive barriers.     

The induction in vitro of adventitious shoots in Rosa

Summary Adventitious shoots were formed on excised leaves, roots and callus of Rosa persica x xanthina and on excised leaves of R. laevigata and R. wichuraiana on culture media that included BAP and NAA as growth regulators. Shoots formed freely on freshly cultured callus of R. persica x xanthina but their production declined in successive cultures and ceased after twelve weeks. Transplantation to soil was improved by rooting plantlets in cellulose plugs in vitro and transferring plantlets to soil while still in the plugs.     

The exploration of genetic resources of Portuguese cabbage and kale for resistance to several Brassica diseases

Summary Twenty three accessions of nine Portuguese cabbage and kale land races from different geographic origins were tested at the seedling stage for resistance to several important brassica diseases. Resistance to downy mildew (Peronospora parasitica), expressed as necrosis of the cotyledon mesophyll, was found in all the accessions. Type A resistance to cabbage yellows (Fusarium oxysporum f. sp. conglutinans race 1) was present in most of the landraces. Resistance to clubroot (Plasmodiophora brassicae race 6) was found in one accession of the Portuguese tree kale. High resistance to blackleg (Leptosphaeria maculans) and white rust (Albuco candida) was not detected, although several accessions showed 20 to 30% of plants with intermediate expression of resistance. All Portuguese cole accessions were susceptible to blackrot (Xanthomonas campestris pv. campestris).     

Production and characterization of intergeneric diploid cybrids derived from symmetric fusion between Microcitrus papuana Swingle and sour orange (Citrus aurantium)

Plants were regenerated from intergeneric somatic hybridization between embryogenic protoplasts of Microcitrus papuana Swingle and leaf-derived protoplasts of sour orange (Citrus aurantium L.) via electrofusion. The regenerated plants were morphologically similar to the leaf parent in growth vigor, leaf and branch structure. FCM analysis showed that they were diploids. Simple-sequence-repeat (SSR) and cleaved-amplified-polymorphic-sequence(CAPS) were employed for hybridity characterization. SSR banding patterns of the regenerated plants were identical to the leaf parent, sour orange, indicating that they possessed nuclear component derived from sour orange. DNA amplification with chloroplast and mitochondrial universal primers, followed by restriction endonuclease digestion, revealed polymorphism between the fusion parents. Therefore, this method was used to determine the cytoplasmic compositions of the regenerated plants. Banding patterns for all the polymorphic primer/enzyme combinations of the regenerated plants were similar to those of the embryogenic parent, M. papuana, suggesting that only the cytoplasmic components derived from the embryogenic parent were present in the regenerated plants. FCM, SSR and CAPS demonstrated that intergeneric diploid cybrids have been successfully obtained by symmetric fusion. Related results concerning nuclear and cytoplasmic composition of previous diploid somatic hybrids and potential mechanism for regeneration of such kind of plants are discussed herein. This revised version was published online in July 2006 with corrections to the Cover Date.