昆虫对转Bt杀虫蛋白基因植物的抗性及其对策

1　引言苏云金杆菌 (Ｂａｃｉｌｌｕｓｔｈｕｒｉｎｇｉｅｎｓｉｓ简称Ｂｔ)是目前世界上产量最大、应用最为成功的微生物杀虫剂 ,除了已筛选出多种Ｂｔ菌株直接发酵培养外 ,还培育出转基因工程菌及转基因植物 ,使Ｂｔ的使用范围大为扩大。Ｂｔ在形成芽孢时产生的伴孢晶体是Ｂｔ杀虫活性的主要来源 ,它可能由几种晶体蛋白即δ -内毒素组成 ,包括Ｃｒｙ和Ｃｙｔ两大类。一般认为 ,δ -内毒素的作用过程要经溶解、酶解活化、与受体结合、插入和孔洞或离子通道形成等五个环节[1] ,涉及到多种毒素和作用位点 ,单一因素的改变对其敏感性影响不大 …     

昆虫对转Bt杀虫蛋白基因植物的抗性及其对策

1 引言 苏云金杆菌(Bacillus thuringiensis 简称Bt)是目前世界上产量最大、应用最为成功的微生物杀虫剂,除了已筛选出多种Bt菌株直接发酵培养外,还培育出转基因工程菌及转基因植物,使Bt的使用范围大为扩大. Bt在形成芽孢时产生的伴孢晶体是Bt杀虫活性的主要来源,它可能由几种晶体蛋白即δ-内毒素组成,包括Cry和Cyt两大类.一般认为,δ-内毒素的作用过程要经溶解、酶解活化、与受体结合、插入和孔洞或离子通道形成等五个环节[1],涉及到多种毒素和作用位点,单一因素的改变对其敏感性影响不大,自50年代到80年代初Bt应用的30多年里,均未有昆虫对之产生抗性的报道,以至于一些研究者曾过分乐观地认为昆虫对Bt 不会产生抗性.进入80年代后,情况发生了急剧变化,相继发现五带淡色库蚊(Culex qu inquefasciatusg)、印度谷螟(Plodia interpunctella)等多种昆虫对Bt产生了抗体[2],同时在田间也发现世界性蔬菜害虫小菜蛾(Plutella xylostella) 对Bt产生了抗生[3-4],世界各国相继开展了昆虫对Bt产生抗性的条件和机制的研究,以期在昆虫还未普遍对Bt产生抗性之前,制定出相应的防治策略,这对于Bt制剂,尤其是转Bt工程菌和转Bt植物的推广使用,具有十分重要的意义.     

Greenhouse tests on resistance management of Bt transgenic plants using refuge strategies

Experimental evaluation of the effectiveness of resistance management tactics is vital to help provide guidelines for the deployment of transgenic insecticidal crops. Transgenic broccoli expressing a Cry1Ac gene of Bacillus thuringiensis (Bt) and the diamondback moth, Plutella xylostella (L.), were used in greenhouse tests to evaluate the influence of size and placement of nontransgenic refuge plants on changes in resistance allele frequency and pest population growth. In the first test with an initial Cry1Ac-resistance (R) allele frequency of 0.007, P. xylostella were introduced into cages with the following treatments: 0, 3.3, 10, 20, and 100% refuge plants. Results after four generations showed that resistance could be delayed by increasing the proportion of refuge plants in the cage. Population growth was also influenced by refuge size with the highest populations occurring in treatments that had either no refuge plants or all refuge plants. In the second test, we evaluated the effect of refuge placement by comparing 20% separate and 20% mixed refuges. P. xylostella with an initial frequency of resistant alleles at 0.0125 were introduced into cages and allowed to cycle; later generations were evaluated for resistance and population growth. Separating the refuge had a pronounced effect on delaying resistance and slowing establishment of resistant larvae on Bt plants. Combining information from both trials, we found a strong negative correlation between the number of larvae on Bt plants and the mortality of the population in leaf dip bioassays. Results from larval movement studies showed that separate refuges delayed resistance better than mixed refuges because they conserved relatively more susceptible alleles than R alleles and did not increase the effective dominance of resistance.     

Field testing for virus resistance and agronomic performance in transgenic plants

Resistance to specific virus diseases may be added as heritable characteristics to susceptible crop cultivars by transformation of the cultivars with specific virus-derived genes. In practice, however, resistance to the virus varies among transformed plants and transformation often changes cultivar yield and quality characteristics that are agronomically important. Therefore, rigorous selection among hundreds of different transformed plant lines is required to identify lines that are both virus resistant and also conform to or exceed standard characteristics of the original, susceptible cultivar. This paper describes methods we have developed for rapid selection of virus resistance, yield, and quality characteristics among transformed populations of plants.     

Dynamically optimal strategies for managing resistance to genetically modified crops

This paper develops a dynamic model of the evolution of pest a population and pest resistance to characterize the socially optimal refuge strategy for managing a pest's resistance to genetically modified crops. Previous theoretical economic analyses of this problem focus on steady states; we also address refuge policies along the optimal path to the final equilibrium. To elaborate on our theoretical analysis of the resistance problem, we develop a simulation model calibrated to cotton (Gossypium spp.) production in China. Our results show the importance of fitness cost as a determinant of the qualitative nature of optimal refuge policies.     

The fitness costs to plants of resistance to pathogens

It has long been predicted that genes giving resistance to pathogens impose a cost on the fitness of plants. A new study has shown this to be true for one resistance gene in Arabidopsis. This raises intriguing theoretical and practical questions about how generally the results apply and how such costs are controlled in plants carrying resistance genes to several different pathogens.     

Novel nanotechnological approaches for managing Phytophthora diseases of plants

Members of the Phytophthora genus are soil-dwelling pathogens responsible for diseases of several important plants. Among these, Phytophthora infestans causes late blight of potatoes, which was responsible for the Irish potato famine during the mid-19th century. Various strategies have been applied to control Phytophthora, including integrated management programs (IMPs) and quarantine, but without successful full management of the disease. Thus, there is a need to search for alternative tools. Here, we discuss the emerging role of nanomaterials in the detection and treatment of Phytophthora species, including slow delivery of agrochemicals (microbicides and pesticides). We propose integrating these tools into an IMP, which could lead to a reduction in pesticide use and provide more effective and sustainable control of Phytophthora pathogens.     

植物同源多倍体耐盐性研究进展

多倍化是高等植物进化最重要的动力之一,多倍体植物由于基因组组成以及基因表达方面的变化,通常会表现出不同的生理现象,多倍体的抗性优于其同源二倍体祖先。土壤盐碱化和次生盐渍化是影响农作物生产的重要因素,严重制约着我国农业的可持续发展。同源多倍体植物耐盐能力较强,是作物遗传改良的重要种质资源,了解其耐盐机理对培育耐盐品种具有重要意义。本文从与盐胁迫相关的耐盐性进化、生理生化水平、细胞结构和分子层面等多角度总结了植物同源多倍体盐胁迫研究进展,并以作者所在研究团队培育出的多倍体西瓜为例讨论了多倍体抗逆性研究存在的问题及未来的发展方向,以期为多倍体抗逆优势机理研究提供参考。     

室内观赏植物对甲醛的吸收及抗逆效果研究

该研究采用密封舱法模拟室内甲醛污染环境(熏蒸箱内甲醛浓度设置为0.1~0.5 mg·m~(-3),熏气时间12 h),对6种常见室内观赏植物进行甲醛熏蒸实验,测定了植物对甲醛的吸收效率、叶面伤害指数及过氧化物酶(POD)等指标。结果表明:这6种常见观赏植物对甲醛均具较好的净化效果,甲醛熏蒸浓度为0.1~0.3 mg·m~(-3),白鹤芋对甲醛的净化效果最好;熏蒸浓度0.5 mg·m~(-3),绿萝和吊兰具有较好的净化和抗逆性能;铁线蕨对甲醛的耐受力较弱,适合作为室内甲醛污染的指示性植物。几种受试植物的POD酶与甲醛吸收率呈显著正相关关系(P0.05),表明植物POD活力变化是受甲醛胁迫后的主要抗逆应答机制之一。     

Transgenic approaches to microbial disease resistance in crop plants

Recent progress in the genetic dissection of plant disease resistance signaling pathways has opened a number of new avenues towards engineering pathogen resistance in crops. Genes controlling race-specific and broad-spectrum resistance responses have been cloned, and novel induced resistance pathways have been identified in model and crop systems. Advances continue to be made in identification of antifungal proteins with effects inhibitory to either pathogen development or accumulation of associated mycotoxins.     

Ammonium enhances resistance to salinity stress in citrus plants

In this work, we demonstrate that NH?? nutrition in citrange Carrizo plants acts as an inducer of resistance against salinity conditions. We investigated its mode of action and provide evidence that NH?? confers resistance by priming abscisic acid and polyamines, and enhances H?O? and proline basal content. Moreover, we observed reduced Cl? uptake as well as enhanced PHGPx expression after salt stress. Control and N-NH?? plants showed optimal growth. However, N-NH?? plants displayed greater dry weight and total lateral roots than control plants, but these differences were not observed for primary root length. Our results revealed that N-NH?? treatment induces a similar phenotypical response to the recent stress-induced morphogenetic response (SIMRs). The hypothesis is that N-NH?? treatment triggers mild chronic stress in citrange Carrizo plants, which might explain the SIMR observed. Moreover, we observed modulators of stress signaling, such as H?O? in N-NH?? plants, which could acts as an intermediary between stress and the development of the SIMR phenotype. This observation suggests that NH?? treatments induce a mild stress condition that primes the citrange Carrizo defense response by stress imprinting and confers protection against subsequent salt stress.     

Studies on the nature of resistance in tomato plants to Verticillium albo-atrum

Extracts of healthy resistant and of healthy susceptible plants of tomato had the same effect on growth of Verticillium albo-atrum in vitro. Tracheal saps from resistant and from susceptible plants showed no difference in their effect on spore germination and mycelial growth of V. albo-atrum. Cuttings from resistant plants, inoculated with V. albo-atrum and fed with low concentrations of casamino acids, or glucose, at first wilted more than controls but soon recovered. Continuous treatment with dilute ethanol solutions for 2 weeks induced marked wilting in inoculated cuttings of resistant plants: treatment for shorter periods caused less severe symptoms, from which cuttings recovered slowly. Metabolic inhibitors did not break resistance of cuttings, but the pathogen survived longer in cuttings treated with sodium diethyldithiocarbamate, salicylaldoxime or 8-hydroxyquinoline than in controls. When one end of segments of stems of resistant plants was inoculated with the pathogen, and 48 h later the uninoculated end was placed near a colony of V. albo-atrum on agar, growth of the fungus colony towards the stem segment was sometimes inhibited. There was no such inhibition when segments from susceptible plants were used. Both tracheal sap and diffusates from segments of inoculated resistant plants supported less growth of germ tubes of V. albo-atrum than sap and diffusates from uninoculated plants. These differences were not obtained with the susceptible variety and production of fungitoxic substances in resistant plants after infection is inferred.     

Homology-dependent resistance: transgenic virus resistance in plants related to homology-dependent gene silencing

Tobacco plants transformed with the RNA polymerase (RdRp) gene of potato virus X (PVX) that are extremely resistant to infection by potato virus X have previously been described. The PVX-resistant plants accumulated the RdRp protein at a lower level than fully susceptible plants transformed with the same RdRp construct. In this paper the difference between the PVX-resistant and susceptible transformed plants is investigated and it is demonstrated that there are three associated phenotypes of the RdRp transgene that vary in parallel between transformed lines. These phenotypes are: accumulation of the transgenic RdRp RNA at a low level; strain-specific resistance to PVX; and the ability of the transgene to trans -inactivate homologous transgenes. This gene-silencing potential of the transgenes conferring PVX resistance was illustrated by analysis of progeny from a cross between a transformant that was extremely resistant to PVX and a second PVX-susceptible transformant. In other transformants, in which the resistance was less extreme, the same three phenotypes were associated but in a transgene dosage-dependent manner. The same association of strain-specific resistance and low-level accumulation of the transgenic RdRp RNA was observed with plants that were transformed with mutant or wild-type versions of the RdRp gene. Strain-specific resistance was also produced in plants transformed with untranslatable versions of the RdRp transgene. Based on these data it is proposed that homology-dependent gene silencing and transgenic resistance to PVX may be due to the same RNA-based mechanism. An undefined genomic feature is proposed to account for the variation in the resistance and trans -inactivation phenotypes of different transformants. It is further proposed that this genome feature influences a cytoplasmic mechanism that degrades RNA with sequence homology to the silencing transgene.     

Field experiments on the resistance of cocoa to cocoa swollen-shoot virus

Progenies from crosses between different Upper Amazon cocoa types and between Upper Amazon and Amelonado were compared for their field resistance to infection with cocoa swollen-shoot virus (CSSV) virulent strain A. Among the intra-Amazon progenies, those from crosses of Scavina, Iquitos and Nanay groups showed most resistance. Progenies from crosses within these groups may have sufficient resistance to be of immediate practical value in reducing crop losses in areas where CSSV is widespread. Some Nanay progenies were more resistant than others and this provides scope for improvement by breeding. Progeny of crosses between Upper Amazon and Amelonado parents were less resistant than those from intra-Amazon crosses. The present results confirm those previously obtained in gauze-house tests on young plants.     

Field screening for resistance to barley net blotch

Inoculation with barley net blotch from infested straw debris was compared with that from diseased plants after sowing infected grains. The straw debris had a high, uniform inoculation potential which gave an early, continuing infection and easily reproducible results that were effective for screening barley cultivars in the field for resistance against a natural population of the pathogen. Further, it minimises an eventual influence from other leaf pathogens coming from the surroundings. Irrigation was decisive for the success of the method - especially in the initial phase. Ten m separation with an immune crop was insufficient to completely prevent infection in the uninoculated plots. The tested 25 cvs were differentiated in six categories of resistant and susceptible on the basis of disease development and final level of attack. None of them was free of symptoms. The most resistant cvs kept a constant, low level of attack during the whole growing season, whereas the most susceptible cvs showed an early and rapidly increasing attack. Intermediate cvs were characterised with more or less slow increase of the attack. The size and proportion of the brown necrotic spots and the surrounding yellow halo varied greatly from one cultivar to the other. The grain yield reduction was due solely to an effect on the thousand grain weight which decreased linearly with the squared point score for net blotch. Further, the disease affected the quality of the grains as less nitrogen was transported from straw to grain in the severely diseased plants.