More Knot Worms: Four New Polygordius (Annelida) Species from the Pacific and Caribbean

Polygordius is a clade of marine annelids mainly seen in coarse-grained habitats. They are notable for their smooth bodies, lacking in chaetae or obvious segments, and they resemble Nematoda or Nemertea. Though Polygordius taxa are found in all oceans of the world, identifying species based only on morphological characters can be challenging due to their relatively uniform external appearances. Diversity within the clade has likely been markedly underestimated. Where morphological characters are inconspicuous or even unreliable, molecular methods can provide clarity in delimiting species. In this study, morphological methods (examination under light and scanning electron microscopy) were integrated with molecular analyses (sequencing of Cytochrome c oxidase subunit I, 16S rRNA and Histone H3 gene fragments) to establish the systematic placement of Polygordius specimens collected from Australia, Belize, French Polynesia, Indonesia, Japan, and the U.S. west coast. These analyses revealed three new species of Polygordius from the Pacific Ocean (P. erikae n. sp., P. kurthcarolae n. sp., and P. kurthsusanae n. sp.) as well as one new species from the Caribbean Sea (P. jenniferae n. sp.). These new species are formally described, and a previously known Japanese species, P. pacificus Uchida, 1936, is redescribed. This study establishes the first molecular data set for Polygordius species from the Pacific region, as well as the first formal description of a Caribbean species of Polygordius. Phylogenetic relationships within Polygordius are summarized and discussed.

Variable Genome Evolution in Fungi After Transposon-Mediated Amplification of a Housekeeping Gene

BackgroundTransposable elements (TEs) can be key drivers of evolution, but the mechanisms and scope of how they impact gene and genome function are largely unknown. Previous analyses revealed that TE-mediated gene amplifications can have variable effects on fungal genomes, from inactivation of function to production of multiple active copies. For example, a DNA methyltransferase gene in the wheat pathogen Zymoseptoria tritici (synonym Mycosphaerella graminicola) was amplified to tens of copies, all of which were inactivated by Repeat-Induced Point mutation (RIP) including the original, resulting in loss of cytosine methylation. In another wheat pathogen, Pyrenophora tritici-repentis, a histone H3 gene was amplified to tens of copies with little evidence of RIP, leading to many potentially active copies. To further test the effects of transposon-aided gene amplifications on genome evolution and architecture, the repetitive fraction of the significantly expanded Pseudocercospora fijiensis genome was analyzed in greater detail.ResultsThese analyses identified a housekeeping gene, histone H3, which was captured and amplified to hundreds of copies by a hAT DNA transposon, all of which were inactivated by RIP, except for the original. In P. fijiensis the original H3 gene probably was not protected from RIP, but most likely was maintained intact due to strong purifying selection. Comparative analyses revealed that a similar event occurred in five additional genomes representing the fungal genera Cercospora, Pseudocercospora and Sphaerulina.ConclusionsThese results indicate that the interplay of TEs and RIP can result in different and unpredictable fates of amplified genes, with variable effects on gene and genome evolution.

High-Resolution Physical Chromosome Mapping of Multigene Families in Lagria villosa (Tenebrionidae): Occurrence of Interspersed Ribosomal Genes in Coleoptera

The organization and mapping of multigene families can produce useful genetic markers, and its use may elucidate the mechanisms of karyotype variation and genomic organization in different groups of eukaryotes. To date, few species of Coleoptera have been analyzed using FISH for the location of multigene families. The purpose of this study was to use high-resolution chromosome mapping to establish the genomic organization of the 18S rDNA, 5S rDNA and histone H3 gene families in Lagria villosa. FISH was performed using 18S rDNA, 5S rDNA and histone H3 probes prepared via PCR labeling. Fiber-FISH for 18S and 5S rDNA indicated that both ribosomal elements are colocalized in the short arm of chromosome 4. Additionally, FISH, using the histone H3 probe, revealed that this sequence is found in only one autosomal pair and did not colocalize with rDNA. Fiber-FISH with 5S and 18S probes, used to improve the mapping resolution of these regions, showed that both genes are closely interspersed with varying amounts of both DNA classes.

First Report of Ilyonectria robusta Causing Rusty Root of Asian Ginseng in China

Asian ginseng (Panax ginseng) is an economically important perennial herb, mainly cultivated in Jilin Province, China. In September 2013, Asian ginseng plants in Jilin showed rusty root symptoms. Typical symptoms included rusty superficial lesions of irregular shapes and margins. Ten symptomatic roots were collected from each of five fields for investigation. To isolate the pathogen, root epidermal tissues with typical lesions were excised, surface-sterilized, and placed on potato dextrose agar (PDA) amended with 50 μg/ml tetracycline. After incubation at 20 ± 1°C in the dark for a week, 18 single-spore isolates out of 50 samples were obtained and identified as Ilyonectria robusta (A.A. Hildebr.) A. Cabral & Crous based on morphological characters and DNA sequence analysis (1). After incubating 7 days on PDA in the dark at 20°C, colonies were cottony to felty in texture and orange white to brownish grey in color with average diameters of 60 ± 3 mm. Isolates were cultured on synthetic nutrient-poor agar for conidial measurements. Macroconidia formed on simple conidiophores predominately, with mostly one and occasionally up to three septa, and were cylindrical with both ends broadly rounded. Macroconidia varied in size depending on the number of cells as follows: one-septate, 7.0 ± 0.6 × 27.7 ± 2.7 μm; two-septate, 7.3 ± 0.7 × 33.3 ± 2.1 μm; three-septate, 7.4 ± 0.6 × 33.4 ± 2.2 μm. Microconidia that formed on complex conidiophores were ellipsoid to ovoid and ranged in size from aseptate 3.7 ± 0.5 × 8.7 ± 1.1 μm to one-septate 5.0 ± 0.6 × 13.1 ± 1.6 μm. Brown chlamydospores were abundantly produced on PDA, globose to subglobose in shape, and in size of 10.9 ± 1.3 × 11.8 ± 1.5 μm (n ≥ 30 observations per structure for each measurement). The isolates were further classified by amplifying and sequencing the ITS1-5.8S rRNA-ITS2 region and histone H3 gene with primer pairs ITS5 and ITS4 (4), and H3-1a and H3-1b (3), respectively. Sequences of the two loci (GenBank Accession Nos. KM015300 and KM015299) showed 100% identity among the three examined isolates and the published I. robusta isolates (JF735268 and JF735517). To confirm the pathogenicity, bare roots of 3-year-old Asian ginseng were inoculated with mycelial plugs of three isolates of I. robusta selected randomly. Four roots were inoculated as replicates for each isolate with pathogen-free agar plugs as a control. One week post-inoculation in the dark at 20 ± 1°C, all the inoculated ginseng roots showed light-brown to dark-brown lesions. I. robusta was recovered from symptomatic roots and confirmed by analyzing the DNA sequence of the histone H3 gene. The inoculation experiment was repeated, and both trials showed the same results. The ginseng tissue under the control agar plugs remained symptomless, and no fungi were isolated. To our knowledge, this is the first report of I. robusta causing rusty root of P. ginseng in China (1,2,5). References: (1) A. Cabral et al. Mycol. Prog. 11:655, 2012. (2) I. Erper et al. Eur. J. Plant Pathol. 136:291, 2013. (3) N. L. Glass et al. Appl. Environ. Microbiol. 61:1323, 1995. (4) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990. (5) X. Lu et al. Plant Dis. 98:1580, 2014.