Origin and Examination of a Leafhopper Facultative Endosymbiont

Eukaryotes engage in intimate interactions with microbes that range in age and type of association. Although many conspicuous examples of ancient insect associates are studied (e.g., Buchneraaphidicola), fewer examples of younger associations are known. Here, we further characterize a recently evolved bacterial endosymbiont of the leafhopper Euscelidius variegatus (Hemiptera, Cicadellidae), called BEV. We found that BEV, continuously maintained in E. variegatus hosts at UC Berkeley since 1984, is vertically transmitted with high fidelity. Unlike many vertically transmitted, ancient endosymbioses, the BEV–E. variegatus association is not obligate for either partner, and BEV can be cultivated axenically. Sufficient BEV colonies were grown and harvested to estimate its genome size and provide a partial survey of the genome sequence. The BEV chromosome is about 3.8 Mbp, and there is evidence for an extrachromosomal element roughly 53 kb in size (e.g., prophage or plasmid). We sequenced 438 kb of unique short-insert clones, representing about 12% of the BEV genome. Nearly half of the gene fragments were similar to mobile DNA, including 15 distinct types of insertion sequences (IS). Analyses revealed that BEV not only shares virulence genes with plant pathogens, but also is closely related to the plant pathogenic genera Dickeya, Pectobacterium, and Brenneria. However, the slightly reduced genome size, abundance of mobile DNA, fastidious growth in culture, and efficient vertical transmission suggest that symbiosis with E. variegatus has had a significant impact on genome evolution in BEV

Four strains of sugarcane mosaic virus infecting cereals and other grasses in Australia

Viruses of the sugar-cane mosaic virus (SCMV)-type were isolated from 23 naturally infected species of Gramineae in Queensland, New South Wales, or the Northern Territory. The virus isolates were placed in four groups or strains on the basis of host reactions. Each strain was named after an important perennial host, viz. (1) Johnson grass (Sorgltum halepense), (2) sugar-cane (Saccharum officinaruin), (3) sabi grass (Urochloa mosambicensis), and (4) Queensland blue couch grass (Digitaria didactyla). The strains could be distinguished on the basis of mosaic or necrotic reactions in Yates NK220Y and Atlas sorghums, on ability to cause systemic infection of Johnson grass or sugar-cane, or local infection of French bean (Phaseolus vulgaris cv. Bountiful). This ability of the sabi grass strain to infect a dicotyledonous host is previously unreported for any strain of SCMV. All four virus strains had a normal particle length of 736±17 nm, but the variability in particle length was greater for the sugar-cane and Queensland blue couch grass strains than for the other two. The Johnson grass strain was only distantly serologicaliy related to the sugar-cane, sabi grass, and Queensland blue couch strains, but the latter three were very closely related amongst themselves. Five aphid species, Aphis craccivora, A. gossypii, Macrosiphum euphorbiae, Rhopalosiphum maidis, and R. padi mere shown to transmit at least one strain of SCMV. A. craccicora and R. maidis were each able to transit all four strains. The Johnson grass strain of SCMV is the major strain infecting maize and sorghum crops in Australia. It was probably the cause of the maize ringspot mottle disease first observed in 1948 and of the mosaic and necrotic diseases of Sorghum almum first observed in 1960. These early records and its distinctive host reactions and serological properties make it unlikely that it is z recent introduction to Australia

Predicting fully self-consistent satellite richness, galaxy growth and starformation rates from the STastical sEmi-Empirical modeL steel

Observational systematics complicate comparisons with theoretical models limiting understanding of galaxy evolution. In particular, different empirical determinations of the stellar mass function imply distinct mappings between the galaxy and halo masses, leading to diverse galaxy evolutionary tracks. Using our state-of-the-art STatistical sEmi-Empirical modeL, STEEL, we show fully self-consistent models capable of generating galaxy growth histories that simultaneously and closely agree with the latest data on satellite richness and star formation rates at multiple redshifts and environments. Central galaxy histories are generated using the central halo mass tracks from state-of-the-art statistical dark matter accretion histories coupled to abundance matching routines. We show that too flat high-mass slopes in the input stellar mass–halo mass relations as predicted by previous works, imply non-physical stellar mass growth histories weaker than those implied by satellite accretion alone. Our best-fitting models reproduce the satellite distributions at the largest masses and highest redshifts probed, the latest data on star formation rates and its bimodality in the local Universe, and the correct fraction of ellipticals. Our results are important to predict robust and self-consistent stellar mass–halo mass relations and to generate reliable galaxy mock catalogues for the next generations of extragalactic surveys such as Euclid and LSST