Shu Hui Koh

Cryptostylis ovata is a terrestrial orchid endemic to southwestern Australia. The virus status of C. ovata has not been studied. Eighty-three C. ovata samples from 16 populations were collected, and sequencing was used to identify RNA viruses from them. In one population, all tested plants were co-infected with isolates of the exotic-to-Australia viruses Ornithogalum mosaic virus (OrMV) and bean yellow mosaic virus (BYMV). In another population, one plant was infected with BYMV. No viruses were detected in the remaining populations. The OrMV isolate shared 98–99% nucleotide identity with isolates identified from wild indigenous Lachenalia (Iridaceae) plants in South Africa. This suggests that the source of OrMV in C. ovata may be one or more bulbous iridaceous flowering plants of southern African origin that were introduced to Western Australia as ornamentals and that have since become invasive weeds. One BYMV isolate from C. ovata also exhibited 99% nucleotide identity with strains isolated from the exotic leguminous crop Lupinus angustifolius in Western Australia, suggesting possible spillover to indigenous species from this source. This study with C. ovata highlights the probable role of invasive weeds and exotic crops as sources of exotic virus spillovers to indigenous plants.

This article presents a “how-to” guide for redesigning an introductory physiology unit to emphasize the Core Concepts of Physiology. Detailed descriptions are provided of innovative, scalable, adjustments to content delivery, assessment, learning objectives, and activities. Staff reflections and student experience suggest a strong Core Concepts emphasis, while challenging, can promote critical thinking and develop an understanding of underlying chemical, physical and biological principles.
This article showcases the redesign of an introductory undergraduate vertebrate physiology unit at Murdoch University (BMS107) to promote student mastery of six Core Concepts of Physiology (Michael J, Cliff W, McFarland J, Modell H, Wright A, SpringerLink. The Core Concepts of Physiology: a New Paradigm for Teaching Physiology, 2017). Concepts were selected for their suitability in an introductory physiology unit and their ability to scaffold advanced physiology learning. Innovative curricular and pedagogical approaches were employed to 1) create a Core Concepts structure, 2) sell the Core Concepts approach to students, 3) foreground Core Concepts in learning materials, 4) actively engage students with Core Concepts, 5) revise, and 6) assess Core Concepts understanding. Median student marks and overall satisfaction with the unit were unaffected by the introduction of a Core Concepts approach. Notably, though, there was a 14% increase in student agreement with the statement “I received feedback that helped me to learn.” The challenge of the Core Concepts approach was articulated by students, but these novice learners also recognized Core Concepts as a mechanism to focus their understanding of physiology and promote critical thinking. For teaching staff, a Core Concepts approach was a reinvigorating opportunity to apply their expertise to the teaching of introductory physiology. We propose that a strong Core Concepts emphasis, while challenging, is highly rewarding for staff and provides students with a “disciplinary passport” that better prepares them to progress in diverse courses and professions. NEW & NOTEWORTHY This article presents a “how-to” guide for redesigning an introductory physiology unit to emphasize the Core Concepts of Physiology. Detailed descriptions are provided of innovative, scalable, adjustments to content delivery, assessment, learning objectives, and activities. Staff reflections and student experience suggest a strong Core Concepts emphasis, while challenging, can promote critical thinking and develop an understanding of underlying chemical, physical and biological principles.

Samples of leaves exhibiting symptoms resembling those caused by virus infection were collected from ornamental street flowers in a rural town in Western Australia. Thirty-seven leaf samples were collected from plants of iris, tulip, lily, daffodil, stock and grape hyacinth. Shotgun sequencing of cDNA derived from leaf samples was done, and analysis showed that about 6% of the sequences obtained were of viral origin. Assembly of virus-like sequences revealed complete or partial genome sequences of 13 virus isolates representing 11 virus species. Eight of the isolates were of potyviruses, one was of a macluravirus, three were of potexviruses, and one was of a bunya-like virus. The complete genome of an isolate originally classified as ornithogalum mosaic virus was genetically divergent and differed in polyprotein cleavage motifs, and we propose that this isolate represents a distinct species. The implications of importing to Australia live plant propagules infected with viruses are discussed.

Tobamoviruses are serious pathogens because they have extremely stable virions, they are transmitted by contact, and they often induce severe disease in crops. Knowledge of the routes of transmission and resilience of tobamovirus virions is essential in understanding the epidemiology of this group of viruses. We used an isolate of the tobamovirus yellow tailflower mild mottle virus (YTMMV) to examine root-to-root transmission in soil and in a hydroponic growth environment. Root-to-root transmission occurred rarely, and when it occurred plants did not exhibit systemic movement of the virus from the roots to the shoots over a 30-day period. The resilience of YTMMV virions was tested in dried leaf tissue over time periods from one hour to one year under temperatures ranging from -80°C to 160°C. Infectivity was maintained for at least a year when incubated at -80°C, 22°C or at fluctuating ambient temperatures of 0.8°C to 44.4°C, but incubation under dry conditions at 160°C for >4 days eliminated infectivity. Exposure of virions to 0.1 M sodium hydroxide or 20% w/v skim milk solution for 30 min, treatments recommended for tobamovirus inactivation, did not abolish infectivity of YTMMV.

Tobamovirus is a group of viruses that have become serious pathogens of crop plants. As part of a study informing risk of wild plant virus spill over to crops, we investigated the capacity of a solanaceous-infecting tobamovirus from an isolated indigenous flora to adapt to new exotic hosts. Yellow tailflower mild mottle virus (YTMMV) (genus Tobamovirus, family Virgaviridae) was isolated from a wild plant of yellow tailflower (Anthocercis littoria, family Solanaceae) and initially passaged through a plant of Nicotiana benthamiana, then one of Nicotiana glutinosa where a single local lesion was used to inoculate a N. benthamiana plant. Sap from this plant was used as starting material for nine serial passages through three plant species. The virus titre was recorded periodically, and 85% of the virus genome was sequenced at each passage for each host. Six polymorphic sites were found in the YTMMV genome across all hosts and passages. At five of these, the alternate alleles became fixed in the viral genome until the end of the experiment. Of these five alleles, one was a non-synonymous mutation (U1499C) that occurred only when the virus replicated in tomato. The mutant isolate harbouring U1499C, designated YTMMV-δ, increased its titre over passages in tomato and outcompeted the wild-type isolate when both were co-inoculated to tomato. That YTMMV-δ had greater reproductive fitness in an exotic host than did the wild type isolate suggests YTMMV evolution is influenced by host changes.

As part of an investigation into viruses of wild plants in Australia, a contiguous sequence of 3935 nucleotides was obtained after shotgun sequencing of RNA isolated from an asymptomatic wild legume, Gompholobium preissii. Phylogenetic analysis of the sequence revealed that it most closely resembled that of Trailing lespedeza virus 1 (TLV1), a virus isolated from a wild legume in America. The proposed virus, named Gompholobium virus A, and TLV1 are genetically closest to viruses in the genera Alphacarmovirus and Pelarspovirus, family Tombusviridae, but they share features distinguishing them from both groups.

Isolates of an Australian indigenous virus, Yellow tailflower mild mottle virus (YTMMV-Kalbarri), and an exotic virus, Pelargonium zonate spot virus (PZSV-SW13), are described from Anthocercis ilicifolia subsp. ilicifolia (red-striped tailflower, family Solanaceae), a species endemic to Western Australia. This is the first report of either virus from this plant species. The complete genome sequences of YTMMV-Kalbarri and of PZSV-SW13 were obtained. YTMMV-Kalbarri shared 97% nucleotide pairwise identity with the sequence of the type isolate YTMMV-Cervantes. The sequence PZSV-SW13 shared greatest sequence identity with the partial sequence of an Australian isolate of PZSV, also from a wild plant, and with a sunflower-derived isolate of PZSV from Argentina. An experimental host range study was done of YTMMV-Kalbarri using cultivated and wild solanaceous and non-solanaceous plants. Most solanaceous plants became systemically infected, with symptoms of systemic infection ranging from symptomless to whole plant necrosis. Based on these studies, it is suggested that YTMMV has the potential to become a pathogen of commercial species of Solanaceae. This study provides further evidence that PZSV is present in wild plants in Australia, in this case an indigenous host species, and possible routes by which it invaded Australia are discussed.

A virus from a symptomatic plant of the gymnosperm Welwitschia mirabilis Hook. growing as an ornamental plant in a domestic garden in Western Australia was inoculated to a plant of Nicotiana benthamiana where it established a systemic infection. The complete genome sequence of 9636 nucleotides was determined using high-throughput and Sanger sequencing technologies. The genome sequence shared greatest identity (83% nucleotides and 91% amino acids) with available partial sequences of catharanthus mosaic virus, indicating that the new isolate belonged to that taxon. Analysis of the phylogeny of the complete virus sequence placed it in a monotypic group in the genus Potyvirus. This is the first record of a virus from W. mirabilis, the first complete genome sequence of catharanthus mosaic virus determined, and the first record from Australia. This finding illustrates the risk to natural and managed systems posed by the international trade in live plants and propagules, which enables viruses to establish in new regions and infect new hosts.

Nicotiana benthamiana is a model plant utilised internationally in plant virology because of its apparent hyper-susceptibility to virus infection. Previously, others showed that all laboratory accessions of N. benthamiana have a very narrow genetic basis, probably originating from a single source. It is unknown if responses to virus infection exhibited by the laboratory accession are typical of the species as a whole. To test this, 23 accessions of N. benthamiana were collected from wild populations and challenged with one to four viruses. Additionally, accessions of 21 other Nicotiana species and subspecies from Australia, one from Peru and one from Namibia were tested for susceptibility to the viruses, and for the presence of a mutated RNA-dependent RNA polymerase I allele (Nb-RDR1m) described previously from a laboratory accession of N. benthamiana. All Australian Nicotiana accessions tested were susceptible to virus infections, although there was symptom variability within and between species. The most striking difference was that plants of a laboratory accession of N. benthamiana (RA-4) exhibited hypersensitivity to Yellow tailflower mild mottle tobamovirus infection and died, whereas plants of wild N. benthamiana accessions responded with non-necrotic symptoms. Plants of certain N. occidentalis accessions also exhibited initial hypersensitivity to Yellow tailflower mild mottle virus resembling that of N. benthamiana RA-4 plants, but later recovered. The mutant Nb-RDR1m allele was identified from N. benthamiana RA-4 but not from any of 51 other Nicotiana accessions, including wild accessions of N. benthamiana, demonstrating that the accession of N. benthamiana used widely in laboratories is unusual.