应用SRAP标记对莲藕资源的聚类分析

利用一种新的分子标记SRAP技术对17个莲藕品种进行了DNA多态性分析。选取7对引物扩增基因组DNA,共获得168条带,其中159条为多态性条带,每对引物平均提供24个标记信息。由UPMGA方法得到的聚类分析结果表明了17个品种间的遗传关系:(1)亚洲莲与美洲莲之间有明显的差异;(2)在亚洲莲内部,藕莲和花莲有明显的遗传分化,在花莲内部亚洲莲与美洲莲的杂交后代和其它花莲品种之间存在明显的差异;(3)SRAP标记是作分子图谱的好标记,但很难区分遗传关系较近的品种。     

Host control over infection and proliferation of a cheater symbiont

Host control mechanisms are thought to be critical for selecting against cheater mutants in symbiont populations. Here, we provide the first experimental test of a legume host’s ability to constrain the infection and proliferation of a native‐occurring rhizobial cheater. Lotus strigosus hosts were experimentally inoculated with pairs of Bradyrhizobium strains that naturally vary in symbiotic benefit, including a cheater strain that proliferates in the roots of singly infected hosts, yet provides zero growth benefits. Within co‐infected hosts, the cheater exhibited lower infection rates than competing beneficial strains and grew to smaller population sizes within those nodules. In vitro assays revealed that infection‐rate differences among competing strains were not caused by variation in rhizobial growth rate or interstrain toxicity. These results can explain how a rapidly growing cheater symbiont – that exhibits a massive fitness advantage in single infections – can be prevented from sweeping through a beneficial population of symbionts.     

The origin, initiation and development of axillary shoot meristems in Lotus japonicus

BACKGROUND AND AIMS: Lotus japonicus 'Gifu' develops multiple axillary shoots in the cotyledonary node region throughout the growth of the plant. The origin, initiation and development of these axillary meristems were investigated. METHODS: Morphological, histological and mRNA in situ analyses were done to characterize the ontogeny of cotyledonary axillary shoot meristems in Lotus. Morphological characterization of a putative Lotus shoot branching mutant (super-accessory branches) sac, is presented. KEY RESULTS: By using expression of an L. japonicus STM-like gene as a marker for meristematic tissues, it was demonstrated that groups of cells maintained in the meristematic state at the cotyledonary axil region coincide with the sites where additional axillary meristems (accessory meristems) form. A Lotus shoot branching mutant, sac, is a putative Lotus branching mutant characterized by increased proliferation of accessory shoots in all leaf axils including the cotyledons. CONCLUSION: In Lotus, axillary shoot meristems continually develop at the cotyledonary node region throughout the growth of the plant. These cotyledonary primary and accessory axillaries arise from the position of a meristematic zone of tissue at the cotyledonary node axil region.     

FRET-based genetically encoded sensors allow high-resolution live cell imaging of Ca²⁺ dynamics

Temporally and spatially defined calcium signatures are integral parts of numerous signalling pathways. Monitoring calcium dynamics with high spatial and temporal resolution is therefore critically important to understand how this ubiquitous second messenger can control diverse cellular responses. Yellow cameleons (YCs) are fluorescence resonance energy transfer (FRET)-based genetically encoded Ca(2+) -sensors that provide a powerful tool to monitor the spatio-temporal dynamics of Ca(2+) fluxes. Here we present an advanced set of vectors and transgenic lines for live cell Ca(2+) imaging in plants. Transgene silencing mediated by the cauliflower mosaic virus (CaMV) 35S promoter has severely limited the application of nanosensors for ions and metabolites and we have thus used the UBQ10 promoter from Arabidopsis and show here that this results in constitutive and stable expression of YCs in transgenic plants. To improve the spatial resolution, our vector repertoire includes versions of YCs that can be targeted to defined locations. Using this toolkit, we identified temporally distinct responses to external ATP at the plasma membrane, in the cytosol and in the nucleus of neighbouring root cells. Moreover analysis of Ca(2+) dynamics in Lotus japonicus revealed distinct Nod factor induced Ca(2+) spiking patterns in the nucleus and the cytosol. Consequently, the constructs and transgenic lines introduced here enable a detailed analysis of Ca(2+) dynamics in different cellular compartments and in different plant species and will foster novel approaches to decipher the temporal and spatial characteristics of calcium signatures.     

A Set of Lotus japonicus Gifu x Lotus burttii Recombinant Inbred Lines Facilitates Map-based Cloning and QTL Mapping

Model legumes such as Lotus japonicus have contributed significantly to the understanding of symbiotic nitrogen fixation. This insight is mainly a result of forward genetic screens followed by map-based cloning to identify causal alleles. The L. japonicus ecotype 'Gifu' was used as a common parent for inter-accession crosses to produce F2 mapping populations either with other L. japonicus ecotypes, MG-20 and Funakura, or with the related species L. filicaulis. These populations have all been used for genetic studies but segregation distortion, suppression of recombination, low polymorphism levels, and poor viability have also been observed. More recently, the diploid species L. burttii has been identified as a fertile crossing partner of L. japonicus. To assess its qualities in genetic linkage analysis and to enable quantitative trait locus (QTL) mapping for a wider range of traits in Lotus species, we have generated and genotyped a set of 163 Gifu × L. burttii recombinant inbred lines (RILs). By direct comparisons of RIL and F2 population data, we show that L. burttii is a valid alternative to MG-20 as a Gifu mapping partner. In addition, we demonstrate the utility of the Gifu × L. burttii RILs in QTL mapping by identifying an Nfr1-linked QTL for Sinorhizobium fredii nodulation.     

Different strategies of Lotus japonicus, L. corniculatus and L. tenuis to deal with complete submergence at seedling stage

Two main strategies allow plants to deal with submergence: (i) escape from below water by means of shoot elongation, or (ii) remaining quiescent under the water until water subsides and then resume growth. We investigated these strategies in seedlings of Lotus japonicus, L. corniculatus and L. tenuis subjected to control and submergence for 12 days, with a subsequent 30-day recovery period. All three species survived submergence but used different strategies. Submerged seedlings of L. japonicus exhibited an escape strategy (emerging from water) as a result of preferential carbon allocation towards shoot mass and lengthening, in detriment to root growth. In contrast, seedlings of L. corniculatus and L. tenuis became quiescent, with no biomass accumulation, no new unfolding of leaves and no shoot elongation. Upon de-submergence, seedlings of L. japonicus had the lowest recovery growth (a biomass and shoot height 58% and 40% less than controls, respectively), L. corniculatus was intermediate and L. tenuis showed the greatest recovery growth. Previously submerged seedlings of L. tenuis did not differ from their controls, either in final shoot biomass or shoot height. Thus, for the studied species, quiescence appears to be an adequate strategy for tolerance of short-term (i.e., 12 days) complete submergence, being consistent with field observations of L. tenuis colonisation of flood-prone environments.     

Efficient isolation, culture and regeneration of Lotus corniculatus protoplasts

This paper reports an improved protocol for isolation, culture and regeneration of Lotus corniculatus protoplasts. A range of parameters which influence the isolation of L. corniculatus protoplasts were investigated, i.e., enzyme combination, tissue type, incubation period and osmolarity level. Of three enzyme combinations tested, the highest yield of viable protoplasts was achieved with the combination of 2% Cellulase Onozuka RS, 1% Macerozyme R-10, 0.5% Driselase and 0.2% Pectolyase. The use of etiolated cotyledon tissue as a source for protoplast isolation proved vital in obtaining substantially higher protoplast yields than previously reported. Culture of the protoplasts on a nitrocellulose membrane with a Lolium perenne feeder-layer on the sequential series of PEL medium was highly successful in the formation of micro-colonies with plating efficiencies 3–10 times greater than previous studies. Shoot regeneration and intact plants were achieved from 46% of protoplast-derived cell colonies.     

莲种子萌发和幼苗生长时期营养物质的代谢变化

莲子叶细胞中储存了丰富的营养物质,主要为蛋白质、淀粉和淀粉质体DNA.这些贮藏物质为种子萌发和幼苗的生长提供必需的能量和养料.通过组织化学和显微镜观察,研究莲从种子萌发到植株生长至具有4个节时,子叶中贮藏物质消耗的全过程.在此过程中,子叶中的贮藏物质不断降解,营养物质发生转运.蛋白体首先发生降解,其大量降解主要发生在幼苗三叶期.淀粉质体降解时会聚集成团,之后体积逐渐减小,最后完全降解.种子萌发后65天是子叶贮藏物质消耗末期,淀粉质体DNA的含量比萌发后20天的三叶期明显减少.细胞壁的形态结构发生多种形式的变化,细胞壁发生的这些变化与子叶细胞间物质的运输有关.含多糖的球形颗粒通过维管束在子叶中运输.