Functional conservation of subfamilies of putative UDP-N-acetylgalactosamine:polypeptide N-acetylgalactosaminyltransferases in Drosophila, Caenorhabditis elegans, and mammals. One subfamily composed of l(2)35Aa is essential in Drosophila

The completed fruit fly genome was found to contain up to 15 putative UDP-N-acetyl-alpha-d-galactosamine:polypeptide N-acetylgalactosaminyltransferase (GalNAc-transferase) genes. Phylogenetic analysis of the putative catalytic domains of the large GalNAc-transferase enzyme families of Drosophila melanogaster (13 available), Caenorhabditis elegans (9 genes), and mammals (12 genes) indicated that distinct subfamilies of orthologous genes are conserved in each species. In support of this hypothesis, we provide evidence that distinctive functional properties of Drosophila and human GalNAc-transferase isoforms were exhibited by evolutionarily conserved members of two subfamilies (dGalNAc-T1 (l(2)35Aa) and GalNAc-T11; dGalNAc-T2 (CG6394) and GalNAc-T7). dGalNAc-T1 and novel human GalNAc-T11 were shown to encode functional GalNAc-transferases with the same polypeptide acceptor substrate specificity, and dGalNAc-T2 was shown to encode a GalNAc-transferase with similar GalNAc glycopeptide substrate specificity as GalNAc-T7. Previous data suggested that the putative GalNAc-transferase encoded by l(2)35Aa had a lethal phenotype (Flores, C., and Engels, W. (1999) Proc. Natl. Acad. Sci. U. S. A. 96, 2964-2969), and this was substantiated by sequencing of three lethal alleles l(2)35Aa(HG8), l(2)35Aa(SF12), and l(2)35Aa(SF32). The finding that subfamilies of GalNAc-transferases with distinct catalytic functions are evolutionarily conserved stresses that GalNAc-transferase isoforms may serve unique biological functions rather than providing functional redundancy, and this is further supported by the lethal phenotype of l(2)35Aa.     

Testing genome skimming for species discrimination in the large and taxonomically difficult genus Rhododendron

Standard plant DNA barcodes based on 2–3 plastid regions, and nrDNA ITS show variable levels of resolution, and fail to discriminate among species in many plant groups. Genome skimming to recover complete plastid genome sequences and nrDNA arrays has been proposed as a solution to address these resolution limitations. However, few studies have empirically tested what gains are achieved in practice. Of particular interest is whether adding substantially more plastid and nrDNA characters will lead to an increase in discriminatory power, or whether the resolution limitations of standard plant barcodes are fundamentally due to plastid genomes and nrDNA not tracking species boundaries. To address this, we used genome skimming to recover near-complete plastid genomes and nuclear ribosomal DNA from Rhododendron species and compared discrimination success with standard plant barcodes. We sampled 218 individuals representing 145 species of this species-rich and taxonomically difficult genus, focusing on the global biodiversity hotspots of the Himalaya-Hengduan Mountains. Only 33% of species were distinguished using ITS+matK+rbcL+trnH-psbA. In contrast, 55% of species were distinguished using plastid genome and nrDNA sequences. The vast majority of this increase is due to the additional plastid characters. Thus, despite previous studies showing an asymptote in discrimination success beyond 3–4 plastid regions, these results show that a demonstrable increase in discriminatory power is possible with extensive plastid genome data. However, despite these gains, many species remain unresolved, and these results also reinforce the need to access multiple unlinked nuclear loci to obtain transformative gains in species discrimination in plants.     

Infection of Sentinel Cotton Aphids (Homoptera: Aphididae) by Aerial Conidia ofNeozygites fresenii(Entomophthorales: Neozygitaceae)

Uninfected adultAphis gossypii(Homoptera: Aphididae) apterae (sentinel aphids) on cotton leaves were exposed for 8 h to the air over a commercial cotton field in Louisiana during the night of 1–2 July 1995. At 0015 h there were 90,437 primary conidia/m³air of the fungusNeozygites fresenii(Entomophthorales: Neozygitaceae) at the midfield position as determined from Rotorod samples. Forty-eight percent (n = 106) of the sentinel aphids exposed for 8 h at midfield were infected by aerial conidia ofN. fresenii.Exposure of sentinel aphids outside the cotton field, at 10 and 100 m downwind and 10 m upwind, resulted in 34.8% (n = 131), 24.0% (n = 129), and 17.4% (n = 146) infected aphids, respectively. These data demonstrate that wind-dispersed aerial conidia ofN. freseniiare infective and rapidly and efficiently disperse the pathogen throughout aphid populations within and between fields.     

Host-range related structural features of the acidic extracellular polysaccharides of Rhizobium trifolii and Rhizobium leguminosarum

Proton nuclear magnetic resonance (1H NMR) and fast atom bombardment mass spectrometric analyses were performed on enzymatically derived oligosaccharides from the acidic excreted polysaccharides (EPS) from representative bacterial strains of the pea-nodulating symbiont, Rhizobium leguminosarum (128C53, 128C63, and 300) and the clover-nodulating symbiont, Rhizobium trifolii (NA-30, ANU843, 0403, TA-1, LPR5035, USDA20.102, and 4S). The results revealed structural similarities and differences between EPS of these two species. Octasaccharide units containing galactose, glucuronic acid, alpha-L-threo-hex-4-enopyranosyluronic acid, and glucose in a molar ratio of 1:1:1:5 were obtained from the EPS of the three R. leguminosarum strains and had the same primary glycosyl sequence and location of pyruvate, acetate, and 3-hydroxybutyrate substituents. About 80% of the galactose residues were acylated with 3-hydroxybutyrate, and there were two acetyl groups per repeating unit distributed between the 2 glucose residues of the main chain-derived sequence of the octasaccharides. In contrast, the R. trifolii strains had varied EPS structures, each of which differed from the common R. leguminosarum EPS structure. The EPS from one group of R. trifolii strains (0403 and LPR5035) most closely resembled the R. leguminosarum EPS but differed in that a lower number of galactose and glucose residues were substituted by 3-hydroxybutyryl and acetyl groups, respectively. The EPS from a second group of R. trifolii strains (ANU843, TA-1, and NA-30) was even more different than the R. leguminosarum EPS. These R. trifolii octasaccharides bore a single acetyl group on O-3 of the glucuronic acid residue. In addition, the level of acylation by 3-hydroxybutyryl groups was 50% of that present in the R. leguminosarum EPS. The remaining two strains of R. trifolii (USDA20.102 and 4S) had very different patterns of acylation to each other and to all of the other strains. The EPS from strain USDA20.102 practically lacked 3-hydroxybutyryl groups and had a unique degree and pattern of acetylation. The oligomers from the EPS of R. trifolii strain 4S completely lacked 3-hydroxybutyryl groups and galactose. The latter EPS contained only one O-1-carboxyethylidene group and had a different degree and pattern of acetylation. Interestingly, these two latter strains differ from the other R. trifolii strains in nodulation rates on rare clover species in the Trifolium cross-inoculation group. Thus, we define several groups of R. trifolii based upon their EPS structures and establish their similarities and distinct differences with the EPS of R. leguminosarum.(ABSTRACT TRUNCATED AT 400 WORDS)     

Taxonomic complexity and breeding system transitions: conservation genetics of the Epipactis leptochila complex (Orchidaceae)

The genus Epipactis contains a problematical complex of autogamous taxa among which species limits are difficult to define. Different authors have treated these plants in different ways, some recognizing the different taxa as distinct species, others considering them as minor intraspecific variants. These contrasting treatments have a direct impact on the conservation resources and status such plants command; 'endemic orchid species' are perceived as having high conservation value, 'localized minor variants' are not. We used allozyme and chloroplast restriction fragment length polymorphism (RFLP) and sequencing analyses to investigate patterns of population genetic structure underlying the taxonomic complexity in this group. Populations of E. dunensis, E. leptochila and E. muelleri were homozygous and uniform for all loci studied here. There were, however, fixed genetic differences among these taxa. Comparisons with published data from the putative progenitor species for the autogamous taxa (the widespread, allogamous E. helleborine) suggest iterative origins of autogamy, rather than the self-pollinating taxa all being merely mutational variants of a single autogamous lineage.     

Global transcriptional response of pig brain and lung to natural infection by Pseudorabies virus

Background  

Pseudorabies virus (PRV) is an alphaherpesviruses whose native host is pig. PRV infection mainly causes signs of central nervous system disorder in young pigs, and respiratory system diseases in the adult.