Isolation and Structure of the Sex Pheromone Inhibitor,iAM373, of Enterococcus faecalis

An Enterococcus faecalis plasmid, pAM373, has a high frequency of transfer in a liquid medium when induced by a recipient-produced sex pheromone, cAM373. The sex pheromone inhibitor against cAM373, termed iAM373, was isolated from a culture supernatant of E. faecalis harboring pAM377 (=pAM373::Tn917), and its structure was identified as a heptapeptide, H-Ser-Ile-Phe-Thr-LeuVal-Ala-OH.     

Identity and combinations of arbuscular mycorrhizal fungal isolates influence plant resistance and insect preference

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RNAi-induced silencing of gene expression in strawberry fruit (Fragaria x ananassa) by agroinfiltration: a rapid assay for gene function analysis

Intron-containing constructs encoding self-complementary 'hairpin' RNA (ihpRNA) have the potential to efficiently silence genes in a range of plant species. In this study we demonstrate the silencing of a ripening-related chalcone synthase (CHS) gene in strawberry fruits (Fragaria x ananassa cv. Elsanta) by a construct (ihpRNA) containing the partial sense and corresponding antisense sequences of CHS separated by an intron obtained from a F. x ananassa quinone oxidoreductase gene. An Agrobacterium strain carrying a T-DNA expressing the ihpRNA transgene was injected with a syringe into the receptacles of growing fruits still attached to the plant about 14 days after pollination. As a consequence of the reduced levels of CHS mRNA and enzymatic CHS activity, the levels of anthocyanins were downregulated and precursors of the flavonoid pathway were shunted to the phenylpropanoid pathway leading to a large increases in levels of (hydroxy) cinnamoyl glucose esters. We anticipate that this technique in combination with metabolite profiling analysis will be useful for studying the function of unknown genes during the development and ripening of strawberry fruit.     

Identification and characterization of simple sequence repeat (SSR) markers from Fragaria×ananassa expressed sequences

The availability of expressed sequence data derived from gene discovery programmes enables mining for simple sequence repeats (SSRs), providing useful genetic markers for crop improvement. These markers are inexpensive, require minimal labour to produce and can frequently be associated with functionally annotated genes. This study reports on the development and characterization of expressed sequence tag (EST)–SSR markers in the cultivated strawberry, Fragaria×ananassa. Fourteen primer pairs were assessed for polymorphism in 13 F.×ananassa genotypes. The markers show reliable amplification and considerable polymorphism, demonstrating the utility of EST–SSRs for genetic analysis of commercial strawberry germplasm.     

'早红'草莓高效遗传转化受体系统的建立

本文以草莓主栽品种'早红'组培苗离体叶片和叶柄为外植体,进行叶龄、暗培养、植物生长调节剂配比及抗生素敏感性研究,建立草莓高效遗传转化的受体系统.在含3.0 mg/L 6-BA与0.1 mg/L 2,4-D的MS培养基上,30 d叶龄的叶片再生频率高达98.31%,平均每叶片再生芽数5.09个,叶柄切段的再生频率为89.25%,平均每叶柄切段再生芽数4.92个,叶片的再生频率略高于叶柄;不定芽在含0.2 mg/L 6-BA与0.2 mg/L GA_3的MS继代培养基上培养成苗.将生长状态良好的不定芽转至含0.2 mg/L IBA的1/2 MS培养基上生根,生根率达100%,平均生根数量16.27条,平均根长1.85 cm.抗生素敏感性试验表明,草莓外植体适宜的卡那霉素选择压力为25 mg/L,头孢霉素的筛选浓度为300mg/L.本研究建立的再生体系可作为草莓遗传转化的受体系统.     

草莓DNA分子标记及其应用

综述了限制性长度多态性(RFLP)、随机扩增多态性DNA(RAPD)、扩增片段长度多态性(AFLP)、简单重复序列(SSR)等不同类型分子标记在草莓指纹图谱构建、品种鉴别、遗传多样性、进化、遗传作图以及相关性状的标记等方面的应用,分析了草莓分子标记研究中的关键问题,提出了今后研究方向。     

Small-scale heterogeneity in soil quality influences photosynthetic efficiency and habitat selection in a clonal plant

BACKGROUND AND AIMS: In clonal plants, internode connections allow translocation of photosynthates, water, nutrients and other substances among ramets. Clonal plants form large systems that are likely to experience small-scale spatial heterogeneity. Physiological and morphological responses of Fragaria vesca to small-scale heterogeneity in soil quality were investigated, together with how such heterogeneity influences the placement of ramets. As a result of their own activities plants may modify the suitability of their habitats over time. However, most experiments on habitat selection by clonal plants have not generally considered time as an important variable. In the present study, how the foraging behaviour of clonal plants may change over time was also investigated. METHODS: In a complex of environments with different heterogeneity, plant performance was determined in terms of biomass, ramet production and photosynthetic activity. To identify habitat selection, the number of ramets produced and patch where they rooted were monitored. KEY RESULTS: Parent ramets in heterogeneous environments showed significantly higher maximum and effective quantum yields of photosystem II than parents in homogeneous environments. Parents in heterogeneous environments also showed significantly higher investment in photosynthetic biomass and stolon/total biomass, produced longer stolons, and had higher mean leaf size than parents in homogeneous environments. Total biomass and number of offspring ramets were similar in both environments. However, plants in homogeneous environments showed random allocation of offspring ramets to surrounding patches, whereas plants in heterogeneous environments showed preferential allocation of offspring to higher-quality patches. CONCLUSIONS: The results suggest that F. vesca employs physiological and morphological strategies to enable efficient resource foraging in heterogeneous environments and demonstrate the benefits of physiological integration in terms of photosynthetic efficiency. The findings indicate that short-term responses cannot be directly extrapolated to the longer term principally because preferential colonization of high-quality patches means that these patches eventually show reduced quality. This highlights the importance of considering the time factor in experiments examining responses of clonal plants to heterogeneity.     

Interaction of Pratylenchus penetrans and Rhizoctonia fragariae in Strawberry Black Root Rot

A split-root technique was used to examine the interaction between Pratylenchus penetrans and the cortical root-rotting pathogen Rhizoctonia fragariae in strawberry black root rot. Plants inoculated with both pathogens on the same half of a split-root crown had greater levels of root rot than plants inoculated separately or with either pathogen alone. Isolation of R. fragariae from field-grown roots differed with root type and time of sampling. Fungal infection of structural roots was low until fruiting, whereas perennial root colonization was high. Isolation of R. fragariae from feeder roots was variable, but was greater from feeder roots on perennial than from structural roots. Isolation of the fungus was greater from structural roots with nematode lesions than from non-symptomatic roots. Rhizoctonia fragariae was a common resident on the sloughed cortex of healthy perennial roots. From this source, the fungus may infect additional roots. The direct effects of lesion nematode feeding and movement are cortical cell damage and death. Indirect effects include discoloration of the endodermis and early polyderm formation. Perhaps weakened or dying cells caused directly or indirectly by P. penetrans are more susceptible to R. fragariae, leading to increased disease.