Duckweed (Lemna minor) and Alfalfa (Medicago sativa) as Bacterial Infection Model Systems.

Alternative animal host models of bacterial infection have been developed which reproduce some of the disease conditions observed in higher animals. Analogously, plants are useful for modeling bacterial pathogenesis, in some cases revealing broadly conserved infection mechanisms. Similar to animals, plants have been shown to possess innate immune systems that respond to invading viruses, bacteria, and fungi. Plant infection models often yield results faster, are more convenient, and less expensive than many animal infection models. Here, we describe the use of two different plant-based infection models for the discovery of virulence genes and factors involved in bacterial pathogenesis.

Culex (Melanoconion) panocossa from peninsular Florida, USA.

Culex (Melanoconion) panocossa is a suspected vector of Venezuelan equine encephalitis virus in Central America. Prior to this report, Cx. panocossa was known from Central America (Belize, Costa Rica, El Salvador, Guatemala, southern Mexico, Panama), northern South America (Colombia, Venezuela) and the Greater Antilles (Cuba and Jamaica). Larvae (n=5) and adults (n=4286) of Cx. panocossa were collected at two locations near Homestead, FL, which indicates substantial established populations of this probable vector species in the continental US. Since larvae of Cx. panocossa are associated with Pistia spp. (water lettuce), the distribution of this mosquito is likely to expand in Florida, where water lettuce is a major invasive plant in freshwater ecosystems. The putative establishment of Cx. panocossa in Florida is of significant concern from a public health perspective, as its proliferation in developed areas could link historically sylvatic transmission foci of Everglades virus with populated centers such as the greater Miami Metropolitan area.

Molecular characterization of Dasheen mosaic virus isolates infecting edible aroids in India.

Dasheen mosaic virus (DsMV) infecting three major edible aroids namely Amorphophallus paeoniifolius, Colocasia esculenta, and Xanthosoma sagittifolium cultivated in India was characterized. Infected plants showing typical DsMV symptoms were subjected to reverse transcription-polymerase chain reaction, and an amplification of a 963 bp fragment which encoded the coat protein (CP) gene was obtained. BLAST analysis of the cloned DNA amplicon revealed the identity of the virus to be that of DsMV. Sequence identity matrix of the nucleotide sequences among the three isolates showed that the DsMV isolate infecting A. paeoniifolius and C. esculenta shared an identity as high as 93%, while the DsMV isolate from X. sagittifolium shared an identity of only 73% and 76% with the DsMV isolates from A. paeoniifolius and C. esculenta, respectively. Comparative analysis of the coat protein of the three DsMV isolates showed the presence of DVG motif (A. paeoniifolius and C. esculenta) and DTG motif in X. sagittifolium and several varying potential threonine and asparagine rich N-glycosylation motifs. Single amino acid substitution of the several conserved motifs occurs in all the three DsMV isolates. This is the first characterization of DsMV isolates infecting A. paeoniifolius, C. esculenta, and X. sagittifolium plants in India.

Identification and molecular characterization of Zantedeschia mild mosaic virus, a new calla lily-infecting potyvirus.

Tissue-cultured seedlings of calla lily (Zantedeschia spp.) with mild mosaic symptom were observed in Taiwan. A new potyvirus, Zantedeschia mild mosaic virus (ZaMMV), was identified in the diseased plants based on the result of ELISA, virion morphology and sequence data. In the host range test, ZaMMV only infected Philodendron selloum and Zantedeschia spp. causing systemic mosaic and mild mosaic symptom, respectively. The 3'-terminal region of the virus was amplified by RT-PCR from total RNA using a potyvirus-specific degenerate primer and an oligo-dT primer. Sequence analysis revealed that the highest amino acid sequence identity of the capsid protein (CP) gene between ZaMMV and thirty potyviruses was 55%, and the highest nucleotide identity of 3' untranslated region (3'UTR) was 52%. Therefore, in terms of species demarcating criteria, ZaMMV is a new species of the genus Potyvirus. From the result of phylogenetic analysis, ZaMMV should be a member of the Bean common mosaic virus subgroup. According to the deduced amino acid sequence of ZaMMV, the N terminus of the CP contained 39 glutamine residues before DAG motif. This unique sequence has never been discovered in plant viruses.

[Molecular identification of Araceae-infecting viruses and their ecology].

A filamentous virus and a spherical virus were detected from partial purification with natural-infected Araceae plants. The filamentous virus was confirmed as dasheen mosaic virus (DsMV) by RNA spot hybridization (RSH) and sequence determination, while the spherical virus was identified as a new strain of cucumber mosaic virus (CMV) by enzyme-linked immunosorbent assay and sequence determination of the 3' end genes of RNA3. CMV was firstly confirmed as one of the principal viruses infecting the Araceae plants under natural condition. According to the sequence similarity of coat protein, Araceae-infecting CMV was then decided belonging to CMV subgroup I, but independent from other isolates in this subgroup. By dot-RNA hybridization to DsMV and CMV probes with total RNA extracted from leaf tissue, field samples collected from some parts of southern China were detected for their natural infection. The infection ratio of field samples infected by DsMV and CMV were 73.3% and 46.7% for samples collected from Hainan Province, 100% and 38.5% for those from Hunan Province, 93.0% and 38.5% for that from Zhejiang Province, and 100% and no infection for samples from Shanghai, respectively. The infection of viruses on Araceae plants was obviously affected by such ecological factors as geological distribution, climate and host species. The occurrence of CMV was greatly influenced by the above factors, but DsMV always existed as the most commonly distributed virus.

Molecular characterisation of an isolate of Dasheen mosaic virus from Zantedeschia aethiopica in China and comparisons in the genus Potyvirus.

The complete nucleotide sequence of an isolate of Dasheen mosaic virus from Zantedeschia aethiopica in Zhejiang Province, China, was determined. The 9991 nucleotide genome was typical of the genus Potyvirus and phylogenetic analysis showed it to be a member of the Bean common mosaic virus subgroup. The 3'-terminal sequence, including the coat protein region, was determined for three further isolates from China and Japan. Variations in the length and composition of the N-terminus of the coat protein were not related to geographic origin or plant host. An analysis of all potyvirus cleavage sites revealed patterns related to phylogenetic groupings.