Immune parameters of QX-resistant and wild caught Saccostrea glomerata hemocytes in relation to Marteilia sydneyi infection

Sydney rock oysters (SRO) Saccostrea glomerata suffer mass mortalities during summer and autumn as a result of infection by a protozoan parasite Marteilia sydneyi (QX disease). Mass selected disease resistant (QXR) lines have been used with some success in affected estuaries in recent years, with resistance attributed to oxidative defense systems. However, the role of hemocytes in resistance to QX by SRO has not been fully explored. In the present study, fifty QXR and fifty wild caught (WC) oysters were collected from a lease at Pimpama River during a QX outbreak in January 2011. Hemocytes characteristics (type, morphology) and functions (mortality, phagocytosis and oxidative activity) from both oyster lines were analyzed by flow cytometry in the context of infection intensity and parasite viability (determined histologically). Amongst the QXR oysters, 20% were diseased containing viable parasite, 74% had killed M. sydneyi and 6% were uninfected. In contrast, 86% of WC oysters were diseased, 2% had killed M. sydneyi and 12% were healthy. Significant differences in hemocyte number and physiology between the two oyster lines were found (ANOVA). Phagocytosis rate and the mean oxidative activity per cell were similar between both oyster lines. Higher numbers of infiltrating and circulating hemocytes, higher percentage of circulating granulocytes, their higher size and complexity in QXR oysters, and the production of reactive oxygen species were associated with the ability to kill the parasite. High abundance of M. sydneyi in the digestive tubule epithelium of both oyster lines implied inability to kill the parasite at the beginning of the infection. However, QXR oysters had the ability to kill M. sydneyi at the stage of sporangiosorae in the epithelium of digestive tubules. The similar phagocytic ability of hemocytes from both oyster lines, the size of the parasite at this infection stage, and its localization suggested that encapsulation is likely to be the main process involved in the eradication of M. sydneyi by QXR oysters.     

Phagocytosis of the protozoan parasite, Marteilia sydneyi, by Sydney rock oyster (Saccostrea glomerata) hemocytes

QX disease is a fatal disease in Sydney rock oysters caused by the protozoan parasite Marteilia sydneyi. The current study investigates the phagocytosis of M. sydneyi by Sydney rock oyster hemocytes. It also compares the in vitro phagocytic activities of hemocytes from oysters bred for QX disease resistance (QXR) with those of wild-type oysters. After ingestion of M. sydneyi, hemocyte granules fused with phagosome membranes and the pH of phagosomes decreased. Significantly (p = <0.05) more phagosomes in QXR hemocytes showed obvious changes in pH within 40 min of phagocytosis, when compared with wild-type hemocytes. Phenoloxidase deposition was also evident in phagosomes after in vitro phagocytosis. Most importantly, ingested and melanised M. sydneyi were detected in vivo among hemocytes from infected oysters. Overall, the data suggest that Sydney rock oyster hemocytes can recognise and phagocytose M. sydneyi, and that resistance against QX disease may be associated with enhanced phagolysosomal activity in QXR oysters.     

Differential proteomic responses of selectively bred and wild‐type Sydney rock oyster populations exposed to elevated CO2

Previous work suggests that larvae from Sydney rock oysters that have been selectively bred for fast growth and disease resistance are more resilient to the impacts of ocean acidification than nonselected, wild‐type oysters. In this study, we used proteomics to investigate the molecular differences between oyster populations in adult Sydney rock oysters and to identify whether these form the basis for observations seen in larvae. Adult oysters from a selective breeding line (B2) and nonselected wild types (WT) were exposed for 4 weeks to elevated pCO₂ (856 μatm) before their proteomes were compared to those of oysters held under ambient conditions (375 μatm pCO₂). Exposure to elevated pCO₂ resulted in substantial changes in the proteomes of oysters from both the selectively bred and wild‐type populations. When biological functions were assigned, these differential proteins fell into five broad, potentially interrelated categories of subcellular functions, in both oyster populations. These functional categories were energy production, cellular stress responses, the cytoskeleton, protein synthesis and cell signalling. In the wild‐type population, proteins were predominantly upregulated. However, unexpectedly, these cellular systems were downregulated in the selectively bred oyster population, indicating cellular dysfunction. We argue that this reflects a trade‐off, whereby an adaptive capacity for enhanced mitochondrial energy production in the selectively bred population may help to protect larvae from the effects of elevated CO₂, whilst being deleterious to adult oysters.     

Proteomic clues to the identification of QX disease-resistance biomarkers in selectively bred Sydney rock oysters,Saccostrea glomerata

The Sydney rock oyster, Saccostrea glomerata, is susceptible to infection by the protozoan parasite, Marteilia sydneyi, the causative agent of QX disease. M. sydneyi infection peaks during summer when QX disease can cause up to 95% mortality. The current study takes a proteomic approach using 2-dimensional electrophoresis and mass spectrometry to identify markers of QX disease resistance among Sydney rock oysters. Proteome maps were developed for QX disease-resistant and -susceptible oysters. Six proteins in those maps were clearly associated with resistance and so were characterized by mass spectrometry. Two of the proteins (p9 and p11) were homologous to superoxide dismutase-like molecules from the Pacific oyster, Crassostrea gigas, and the Eastern oyster, Crassostrea virginica. The remaining S. glomerata proteins had no obvious similarities to known molecules in sequence databases. p9 and p11 are currently being investigated as potential markers for the selective breeding of QX disease-resistant oysters.     

Assessment of genetic diversity and population structure in cultured Australian Pacific oysters

The recent development of Pacific oyster (Crassostrea gigas) SNP genotyping arrays has allowed detailed characterisation of genetic diversity and population structure within and between oyster populations. It also raises the potential of harnessing genomic selection for genetic improvement in oyster breeding programmes. The aim of this study was to characterise a breeding population of Australian oysters through genotyping and analysis of 18 027 SNPs, followed by comparison with genotypes of oyster sampled from Europe and Asia. This revealed that the Australian populations had similar population diversity (H_E) to oysters from New Zealand, the British Isles, France and Japan. Population divergence was assessed using PCA of genetic distance and revealed that Australian oysters were distinct from all other populations tested. Australian Pacific oysters originate from planned introductions sourced from three Japanese populations. Approximately 95% of these introductions were from geographically, and potentially genetically, distinct populations from the Nagasaki oysters assessed in this study. Finally, in preparation for the application of genomic selection in oyster breeding programmes, the strength of LD was evaluated and subsets of loci were tested for their ability to accurately infer relationships. Weak LD was observed on average; however, SNP subsets were shown to accurately reconstitute a genomic relationship matrix constructed using all loci. This suggests that low‐density SNP panels may have utility in the Australian population tested, and the findings represent an important first step towards the design and implementation of genomic approaches for applied breeding in Pacific oysters.     

Melanism and disease resistance in insects

There is growing evidence that insects in high-density populations invest relatively more in pathogen resistance than those in low-density populations (i.e. density-dependent prophylaxis). Such increases in resistance are often accompanied by cuticular melanism, which is characteristic of the high-density form of many phase polyphenic insects. Both melanism and pathogen resistance involve the prophenoloxidase enzyme system. In this paper the link between resistance, melanism and phenoloxidase activity is examined in Spodoptera larvae. In S. exempta , cuticular melanism was positively correlated with phenoloxidase activity in the cuticle, haemolymph and midgut. Melanic S. exempta larvae were found to melanize a greater proportion of eggs of the ectoparasitoid Euplectrus laphygmae than non-melanic larvae, and melanic S. littoralis were more resistant to the entomopathogenic fungus Beauveria bassiana (in S. exempta the association between melanism and fungal resistance was non-signficant). These results strengthen the link between melanism and disease resistance and implicate the involvement of phenoloxidase.     

鸭茅种质资源多样性研究进展

鸭茅是世界范围内广泛栽培的一种重要禾本科牧草,具有高产、优质、耐荫性强等特性。我国的野生鸭茅资源十分丰富,分布广泛,基因资源优良,但有关鸭茅的研究报导相对较少。为了更好地开发利用这一优良的牧草资源,本从形态学、细胞学和分子水平对国内外鸭茅种质资源多样性的研究进行了综述,并对今后我国的鸭茅研究工作提出了建议。     

蓖麻根腐病抗性鉴定及其SSR标记的初步建立

蓖麻根腐病是茄腐镰孢菌(Fusarium solani)引起的根部病害,严重影响蓖麻产量。抗源缺乏制约了抗病品种的选育。为寻找抗病种质、建立抗性分子标记,该研究对252份蓖麻材料的抗性进行了表型和分子标记鉴定。结果表明:(1)浓度为1×10⁶个·mL^-1的孢子悬浮液灌根是一种有效的接种方法; 以接种后枯萎天数为基础的5级评价法,可作为鉴定标准。(2)鉴定出130份抗病材料,其中高抗为105份。(3)野生材料中抗病材料比率(66%)远高于栽培材料(35%),建议将野生材料,尤其是中国华南野生材料的研究利用作为今后抗病育种的重要方向。(4)初步建立了8个与抗性关联的SSR标记。该研究结果提供了有效的根腐病抗性鉴定方法和评价标准,筛选出了一批育种迫切需要的抗病基因资源,初步建立了可用于辅助选择的SSR标记,为蓖麻抗根腐病育种奠定了重要基础。     

Symbiont-mediated adaptation by planthoppers and leafhoppers to resistant rice varieties

For over 50 years, host plant resistance has been the principal focus of public research to reduce planthopper and leafhopper damage to rice in Asia. Several resistance genes have been identified from native varieties and wild rice species, and some of these have been incorporated into high-yielding rice varieties through conventional breeding. However, adaptation by hoppers to resistant rice has been phenomenally rapid, and hopper populations with virulence against several resistance genes are now widespread. Directional genetic selection for virulent hoppers seems unlikely given the rapid pace of adaptation reported from field and laboratory studies. Among the alternative explanations for rapid hopper adaptation are changes (genetic, epigenetic, or community structure) in endosymbiont communities that become advantageous for planthoppers and leafhoppers that feed on resistant rice varieties. This review examines the nature of these symbiont communities and their functions in planthoppers and leafhoppers—focusing on their likely roles in mediating adaptation to plant resistance. Evidence from a small number of experimental studies suggests that bacterial and eukaryotic (including yeast-like) symbionts can determine or mediate hopper virulence on rice plants and that symbiont functions could change over successive generations of selection on both resistant and susceptible plants. The review highlights the potential complexity of rice hopper–symbiont interactions and calls for a more careful choice of research materials and methods to help reduce this complexity. Finally, the consequences of symbiont-mediated virulence adaptation for future rice breeding programs are discussed.     

烟草赤星病抗性主效QTL人工选择响应研究

分析赤星病抗性主效QTL的人工选择响应,可为烟草赤星病抗性分子标记辅助选择提供一定的理论基础。本研究利用与主效QTL紧密连锁的分子标记J9和J4,分析随机群体、人工选择群体和自然群体中响应分子标记的等位基因频率,研究相关标记位点在不同群体中的等位基因变化规律。结果发现:(1)赤星病抗性主效QTL等位基因在不同选择强度(5%、10%和20%)的正向选择条件下均发生了显著性偏分离,其中在10%的正向选择强度下偏分离显著性最高。(2)在不同世代(F3、F4、F5和F6)的赤星病抗性育种选择群体中,J9位点抗病亲本等位基因型频率显著高于感病亲本基因型频率,表明来源于抗源净叶黄的主效抗性QTL与赤星病抗性显著关联。(3)在198份自然群体中,包括烟草赤星病抗性品种中烟86、单育二号在内的50份烟草种质携带与抗源净叶黄相同的基因型,表明该主效QTL被广泛应用于烟草赤星病抗性改良中。本研究验证了之前定位到的主效抗病QTL的准确性;分析了该主效QTL的人工选择响应,相关结果为烟草赤星病抗性改良提供了一定的理论基础。     

Phenotypic selection for dormancy introduced a set of adaptive haplotypes from weedy into cultivated rice

Association of seed dormancy with shattering, awn, and black hull and red pericarp colors enhances survival of wild and weedy species, but challenges the use of dormancy genes in breeding varieties resistant to preharvest sprouting. A phenotypic selection and recurrent backcrossing technique was used to introduce dormancy genes from a wild-like weedy rice to a breeding line to determine their effects and linkage with the other traits. Five generations of phenotypic selection alone for low germination extremes simultaneously retained dormancy alleles at five independent QTL, including qSD12 (R(2) > 50%), as determined by genome-wide scanning for their main and/or epistatic effects in two BC(4)F(2) populations. Four dormancy loci with moderate to small effects colocated with QTL/genes for one to three of the associated traits. Multilocus response to the selection suggests that these dormancy genes are cumulative in effect, as well as networked by epistases, and that the network may have played a "sheltering" role in maintaining intact adaptive haplotypes during the evolution of weeds. Tight linkage may prevent the dormancy genes from being used in breeding programs. The major effect of qSD12 makes it an ideal target for map-based cloning and the best candidate for imparting resistance to preharvest sprouting.     

Fertility,Inheritance and Amino Acid Analysis of Lysine Plus Threonine-Resistant Mutant Progenies of Maize

Sixth generation of mutant maize seed homozygous for lysine plus threonine resistancewhich was derived from the resistant callus cultures has been harvested. The resistance could be inherited stably. The fertility, however, was very poor. The resistant homozygotes have been obtained by backcross of the wild type with the resistant plants (W77-R3019 ×R0), and their fertility could be parlty recovered after selection for the resistant plants from backcross progenies. Genetic analysis showed that the resistance inherited as a single dominant nuclear allele. All of the free amino acids except phenylalan inc in the homozygote are increased by 4 folds. and free essential amino acids by 5 folds which are higher than those in the wild types. Total amino acids increased by 5.53%. The dramatic increase (11 times) in free threonine adds up the total threonine by 17.73%. Difference of the protein content between the homozygote and wild type was not obvious. These results show that selection for the resistance to lysine plus threonine in maize and other cereals is probably very useful for improving their value of protein nutrition.     

Selectively bred oysters can alter their biomineralization pathways,promoting resilience to environmental acidification

Commercial shellfish aquaculture is vulnerable to the impacts of ocean acidification driven by increasing carbon dioxide (CO₂) absorption by the ocean as well as to coastal acidification driven by land run off and rising sea level. These drivers of environmental acidification have deleterious effects on biomineralization. We investigated shell biomineralization of selectively bred and wild‐type families of the Sydney rock oyster Saccostrea glomerata in a study of oysters being farmed in estuaries at aquaculture leases differing in environmental acidification. The contrasting estuarine pH regimes enabled us to determine the mechanisms of shell growth and the vulnerability of this species to contemporary environmental acidification. Determination of the source of carbon, the mechanism of carbon uptake and use of carbon in biomineral formation are key to understanding the vulnerability of shellfish aquaculture to contemporary and future environmental acidification. We, therefore, characterized the crystallography and carbon uptake in the shells of S. glomerata, resident in habitats subjected to coastal acidification, using high‐resolution electron backscatter diffraction and carbon isotope analyses (as δ¹³C). We show that oyster families selectively bred for fast growth and families selected for disease resistance can alter their mechanisms of calcite crystal biomineralization, promoting resilience to acidification. The responses of S. glomerata to acidification in their estuarine habitat provide key insights into mechanisms of mollusc shell growth under future climate change conditions. Importantly, we show that selective breeding in oysters is likely to be an important global mitigation strategy for sustainable shellfish aquaculture to withstand future climate‐driven change to habitat acidification.     

小麦抗赤霉病外源种质的创制和育种利用

小麦赤霉病是危害小麦安全生产的重要病害之一,种植抗病品种是防治赤霉病最经济有效的手段。目前在生产上应用的抗源很少,越来越多的研究者将目光转移到小麦的近缘属种,寻找新的抗源以及寻求新的育种突破。携带抗性基因的外源染色体可以通过染色体工程手段以附加系、代换系和易位系等形式导入小麦。综述了将大赖草等多个小麦近缘种的抗赤霉病基因导入普通小麦、创制抗病外源种质和育种利用的最新研究进展,以期为小麦抗赤霉病育种提供参考信息。     

利用微卫星标记鉴定水稻的稻瘟病抗性

应用水稻稻瘟病抗性基因Pid(t)紧密连锁的微卫星标记RM262对含有该抗病基因的品种地谷与感病品种江南香糯和8987的杂交F2群体进行遗传分析和抗性鉴定,结果表明,RM262的PCR扩增物在抗、感品种之间的多态性较好;在2个F2群体中,RM262和抗病基因间的重组率分别为5.74%和8.17%,应用该标记的抗性纯合和杂合带型选择抗性植株,其准确率可达98%以上。此外,还就分子标记辅助育种进行了讨论。     

Inheritance of resistance to leaf and glume blotch caused by Septoria nodorum Berk. in winter wheat

Sixteen crosses between eight winter wheat cultivars were screened for resistance to Septoria nodorum leaf and glume blotch in the F₁ and F₄ generations using artificial inoculation in the field. The F₁ of most crosses showed dominance for susceptibility on both ear and leaf. The effects of general combining ability were of similar magnitude as the effects for specific combining ability. On the basis of the phenotypic difference of the parents, no prediction was possible about the amount and the direction of genetic variance in the segregating populations. The variation observed in this study both within and among the segregating populations suggests a quantitative inheritance pattern influencing the expression of the two traits. The components of variance between F₂ families within a population were as high as (for S. nodorum blotch on the ear) or higher (for S. nodorum blotch on the leaf) than those between populations. Therefore, strong selection within a few populations may be as effective to obtain new resistant genotypes as selection in a large number of populations. In almost all crosses, progenies were found that were more resistant than the better parent. Thus transgression breeding may be a tool to breed for higher levels of resistance to S. nodorum blotch. Highly resistant genotypes were found even in combination with two susceptible parents. The genetic source for Septoria resistance is probably broader than is generally assumed and could be used to improve S. nodorum resistance by combination breeding followed by strong selection in large populations. Received: 18 January / Accepted: 30 April 1999     

Kin groups and trait groups: population structure and epidemic disease selection

A Monte Carlo simulation based on the population structure of a small-scale human population, the Semai Senoi of Malaysia, has been developed to study the combined effects of group, kin, and individual selection. The population structure resembles D.S. Wilson's structured deme model in that local breeding populations (Semai settlements) are subdivided into trait groups (hamlets) that may be kin-structured and are not themselves demes. Additionally, settlement breeding populations are connected by two-dimensional stepping-stone migration approaching 30% per generation. Group and kin-structured group selection occur among hamlets the survivors of which then disperse to breed within the settlement population. Genetic drift is modeled by the process of hamlet formation; individual selection as a deterministic process, and stepping-stone migration as either random or kin-structured migrant groups. The mechanism for group selection is epidemics of infectious disease that can wipe out small hamlets particularly if most adults become sick and social life collapses. Genetic resistance to a disease is an individual attribute; however, hamlet groups with several resistant adults are less likely to disintegrate and experience high social mortality. A specific human gene, hemoglobin E, which confers resistance to malaria, is studied as an example of the process. The results of the simulations show that high genetic variance among hamlet groups may be generated by moderate degrees of kin-structuring. This strong microdifferentiation provides the potential for group selection. The effect of group selection in this case is rapid increase in gene frequencies among the total set of populations. In fact, group selection in concert with individual selection produced a faster rate of gene frequency increase among a set of 25 populations than the rate within a single unstructured population subject to deterministic individual selection. Such rapid evolution with plausible rates of extinction, individual selection, and migration and a population structure realistic in its general form, has implications for specific human polymorphisms such as hemoglobin variants and for the more general problem of the tempo of evolution as well.     

Immune function responds to selection for cuticular colour in Tenebrio molitor

Cuticular colour in the mealworm beetle (Tenebrio molitor) is a quantitative trait, varying from tan to black. Population level variation in cuticular colour has been linked to pathogen resistance in this species and in several other insects: darker individuals are more resistant to pathogens. Given that cuticular colour has a heritable component, we have taken an experimental evolution approach: we selected 10 lines for black and 10 lines for tan adult cuticular phenotypes over at least six generations and measured the correlated responses to selection in a range of immune effector systems. Our results show that two immune parameters related to resistance (haemocyte density and pre-immune challenge activity of phenoloxidase (PO)) were significantly higher in selection lines of black beetles compared to tan lines. This may help to explain increased resistance to pathogens in darker individuals. Cuticular colour is dependent upon melanin production, which requires the enzyme PO that is present in its inactive form inside haemocytes. Thus, the observed correlated response to selection upon cuticular colour and immune variables probably results from these traits' shared dependence on melanin production.     

野生大豆资源对大豆疫病抗病性和耐病性鉴定

大豆疫病是大豆重要病害之一,在世界范围内导致严重经济损失。防治大豆疫病最有效方法是利用抗病或耐病品种。筛选抗性资源是发掘抗性基因和抗病育种的基础。本研究鉴定了野生大豆资源对大豆疫病的抗病性和耐病性,以期发掘优异抗源。苗期用子叶贴菌块方法鉴定104份野生大豆资源对两个不同毒力的大豆疫霉分离物PSJS2(毒力型:1a,1b,1c,1d,1k,2,3a,3b,3c,4,5,6,7,8)和PS41-1(毒力型:1a,1d,2,3b,3c,4,5,6,7,8)抗性,结果表明33份资源抗PS41-1,35份资源抗PSJS2,其中18份抗两个分离物。在抗病性鉴定基础性上,用菌层接种方法对选择的82份资源进行耐病性鉴定,发现7份高耐病性资源。这些结果表明,野生大豆中可能含有新的大豆疫病抗病和(或)耐病资源,这些抗病或耐病资源可以用于未来大豆抗病育种,以丰富大豆对大豆疫病的抗性遗传基础。