Molecular Diagnosis of the Causal Agent of the Root and Corm Rot of Taro (Colocasia esculenta) in the Aunu’u Island of American Samoa

Recently, taro (Colocasia esculenta) growers in Aunu’u have been complaining of a new disease characterized by the taro root and corm rot. Pythium spp. usually cause this type of disease. But, it was puzzling when the morphological features of the fungus isolated from diseased taros did not match those of Pythium. More sophisticated tools were needed. The objective of this study was to use molecular techniques for identification of this pathogen. Potato dextrose broth (PDB) was inoculated with five agar plugs cut from one week-old pure cultures of the pathogen grown on potato dextrose agar (PDA). After 10 days incubation at 24 C, mycelia were collected by centrifugation, and genomic DNA was extracted, using the CTAB method. The DNA was used to PCR-amplify a fragment of the ITS-rRNA gene, using universal fungal ITS primers. The amplicons were sequenced with BigDye Terminator V3.1, and the reactions were shipped to Hawaii for resolution on a DNA analyzer. The Sequencher software was used to build a 795-nt consensus sequence, which was submitted for similarity searches, using the NCBI Blast program. The Blast search returned Phytophthora taxon cyperaceae as the best match. This the first time this species of Phytophthora is implicated on taro disease

Survey of Virus Diseases of Taro, Colocasia esculenta, on the Aunu’u Island of American Samoa

Taro, Colocasia esculenta, is the most important staple crop in American Samoa, especially in Aunu’u, a small (1.5 km2) island, approximately 2 km southeast of the main island of Tutuila. However, the sustainability of taro production is threatened by the occurrence of numerous diseases and pests, as evidenced by the leaf blight (Phytophthora colocasiae) epidemic that devastated the Samoan taro production in early 1990s. Crop losses due to viruses alone have been estimated at 20 - 60%. The objective of this study was to investigate the incidence of virus diseases of taro in Aunu’u. Overall, 112 leaf samples, mostly (85%) from cultivars “Talo Manua” and “Palau 10”, were collected from seven major farms on the Island. Genomic DNA and total RNA were extracted from each sample, and the extracts subjected to PCR and RT-PCR, using primers that amplify specific regions of the target virus genome. The reactions were resolved on 1.5% agarose gel electrophoresis, and gels were analyzed using a GelDoc EZ documentation system. Dasheen Mosaic Virus (DsMV) was the predominant virus in Aunu’u, infecting 79% of plants, followed by Taro Bacilliform Virus (TaBV), with 46%. Many (40%) of the plants infected with DsMV were co-infected with TaBV. Cultivar “Talo Manua” was more susceptible to both viruses than “Palau 10”. No other taro virus was detected. This is the first report on taro virus diseases in Aunu’u. It would be desirable to extend this type of survey to other islands of American Samoa

Prospectus, October 27, 1999

https://spark.parkland.edu/prospectus_1999/1027/thumbnail.jp

Prospectus, September 29, 1999

https://spark.parkland.edu/prospectus_1999/1023/thumbnail.jp

Evidence for diversifying selection of genetic regions of encoding putative collagen-like host-adhesive fibers in Pasteuria penetrans

© FEMS 2018. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.Pasteuria spp. belong to a group of genetically diverse endospore-forming bacteria (phylum: Firmicutes) that are known to parasitize plant-parasitic nematodes and water fleas (Daphnia spp.). Collagen-like fibres form the nap on the surface of endospores and the genes encoding these sequences have been hypothesised to be involved in the adhesion of the endospores of Pasteuria spp. to their hosts. We report a group of 17 unique collagen-like genes putatively encoded by Pasteuria penetrans (strain: Res148) that formed five different phylogenetic clusters and suggest that collagen-like proteins are an important source of genetic diversity in animal pathogenic Firmicutes including Pasteuria. Additionally, and unexpectedly, we identified a putative collagen-like sequence which had a very different sequence structure to the other collagen-like proteins but was similar to the protein sequences in Megaviruses that are involved in host-parasite interactions. We, therefore, suggest that these diverse endospore surface proteins in Pasteuria are involved in biological functions, such as cellular adhesion; however, they are not of monophyletic origin and were possibly obtained de novo by mutation or possibly through selection acting upon several historic horizontal gene transfer events.Peer reviewedFinal Published versio

Central CD4+ T cell tolerance: deletion versus regulatory T cell differentiation

The diversion of MHC class II-restricted thymocytes into the regulatory T (Treg) cell lineage, similarly to clonal deletion, is driven by intrathymic encounter of agonist self-antigens. Somewhat paradoxically, it thus seems that the expression of an autoreactive T cell receptor is a shared characteristic of T cells that are subject to clonal deletion and those that are diverted into the Treg cell lineage. Here, we discuss how thymocyte-intrinsic and -extrinsic determinants may specify the choice between these two fundamentally different T cell fates

Legume Genomics and Breeding

This chapter contains sections titled; Introduction; Constraints in Crop Production; Genomic Resources in Legumes;Trait Mapping and Marker-Assisted Selection; Summary and Prospects; Acknowledgments; Literature Cite

Entry, Capture and Presentation of Blood-Borne Antigens and Effects of TCR Ligand Density on Negative Selection and Treg Induction of CD4SP Thymocytes

The thymus employs two primary mechanisms to maintain self-tolerance: negative selection and the generation of regulatory T-cells (Treg). Both of these processes require the effective presentation of self-antigens whether derived intra-thymically or from the periphery. Here, we used Hen egg-white lysozyme (HEL) as a model antigen administered i.v. to examine the entry, presentation and effect of blood-borne antigens on thymic T-cell selection. Previous studies on Treg generation and negative selection have shown a requirement for high avidity T-cell receptor (TCR)/peptide-MHC (pMHC) interaction with agonist ligands presented on thymic antigen presenting cells (APC). However, the quantitative differences between signals that induce deletion of self-reactive T-cells by negative selection and those that induce differentiation of self-reactive T-cells into Treg remain elusive. Additionally, the contribution of different APC in determining whether thymocytes undergo negative selection or become Treg is unclear, especially in the case of blood-de rived antigens. We found that thymic architecture modulates the amount of antigen that enters the thymus and consequently the level of pMHC density presented. There was size-dependent entry of proteins into the thymus. Less than 0.5 % of the injected HEL entered the thymus and presentation resulted in Treg induction and/or negative selection in TCR transgenic mice specific for the major and minor epitopes of HEL that depended on peptide-MHC density levels. Both the range of antigen dose and pMHC complexes that led to negative selection compared to Treg induction for both T-cells was distinct although there was some overlap. More than 25 pMHC complexes per DC were estimated to initiate negative selection with even lower pMHC complexes inducing Treg. Thus, despite the limiting amounts of antigen that entered, the efficiency of thymic antigen presentation resulted in a remarkable effect on thymocyte selection. Despite disproportionate uptake, blood-borne HEL was presented primarily by Sirpα+ and CD8α+ conventional thymic dendritic cells (cDC), with minimal presentation by other DC subsets and thymic epithelial cells ( TEC ). Both cDC subsets induced Treg and negative selection to in vivo captured HEL to a similar extent. Further, in Ba tf3-/-mice, which have significantly reduced CD8α+ cDC but an intact Sirpα+ cDC population, the presentation of blood-borne HEL was unaffected suggesting that CD8α+ cDC cells are dispensable. There was minimal contribution of peripheral APC, particularly blood Sirpα+ cDC, in the entry and presentation of blood-borne HEL. These data suggest that the effects on thymocytes are mediated primarily by cDC localized within the thymus rather than circulating APC. Together, our results emphasize the sensitivity of both negative selection and Treg induction to pMHC density levels ensuring that central tolerance will be effective regardless of limitations imposed by local antigen expression

Thymus-Blood Protein Interactions Are Highly Effective in Negative Selection and Regulatory T Cell Induction

Using hen egg-white lysozyme, the effect of blood proteins on CD4 thymic cells was examined. A small fraction of i.v. injected hen egg-white lysozyme rapidly entered the thymus into the medulla. There it was captured and presented by dendritic cells (DCs) to thymocytes from two TCR transgenic mice, one directed to a dominant peptide and a second to a poorly displayed peptide, both presented by MHC class II molecules I-Ak. Presentation by DC led to negative selection and induction of regulatory T cells, independent of epithelial cells. Presentation took place at very low levels, less than 100 peptide-MHC complexes per DC. Such low levels could induce negative selection, but even lower levels could induce regulatory T cells. The anatomy of the thymus-blood barrier, the highly efficient presentation by DC, together with the high sensitivity of thymic T cells to peptide-MHC complexes, results in blood protein Ags having a profound effect on thymic T cells