Sequence diversity in the coat protein coding region of the genome RNA of Johnsongrass mosaic virus in Australia

Sequence diversity in the coat protein coding region of Australian strains of Johnsongrass mosaic virus (JGMV) was investigated. Field isolates were sampled during a seven year period from Johnsongrass, sorghum and corn across the northern grain growing region. The 23 isolates were found to have greater than 94% nucleotide and amino acid sequence identity. The Australian isolates and two strains from the U.S.A. had about 90% nucleotide sequence identity and were between 19 and 30% different in the N-terminus of the coat protein. Two amino acid residues were found in the core region of the coat protein in isolates obtained from sorghum having the Krish gene for JGMV resistance that differed from those found in isolates from other hosts which did not have this single dominant resistance gene. These amino acid changes may have been responsible for overcoming the resistance conferred by the Krish gene for JGMV resistance in sorghum. The identification of these variable regions was essential for the development of durable pathogen-derived resistance to JGMV in sorghum.

Cone visual pigments and retinal mosaics in the striped marlin

Three different cone photoreceptor visual pigments in the retina of striped marlin Tetrapturus audax were found with the aid of microspectrophotometry. This provides the first evidence for the basis of colour vision in the Istiophoridae. Furthermore, regional variations in photoreceptor density, type and spatial arrangement indicate differing visual capabilities along different visual axes. (C) 2003 The Fisheries Society of the British Isles.

A new species of Glaphyromorphus (Reptilia : Scincidae) from Mt Elliot, north-eastern Queensland

Glaphyromorphus clandestinus, sp. nov., is described from granite-slab habitat on Mt Elliot, north-eastern Queensland. This species can be distinguished from its congeners by a combination of the following characters: large size (SVL 72 mm), adpressed limbs of adult separated by noticeably more than the length of the forelimb, 26 mid-body scale rows, and flanks patterned with dark flecks forming a series of longitudinal lines. The distribution, habitat preferences and habits of this species are poorly known. Currently G. clandestinus is known from a single locality where individuals have been found in an exposed area of exfoliating granite, set in a mosaic of rainforest and eucalyptus woodland. The discovery of this species brings to three the number of vertebrate species known to be endemic to Mt Elliot and highlights the evolutionary significance of this southerly outlier to the mountainous rainforest of the Wet Tropics.

Etr1-1 gene expression alters regeneration patterns in transgenic lettuce stimulating root formation

We have evaluated the transformation efficiency of two lettuce ( Lactuca sativa L.) cultivars, LE126 and Seagreen, using Agrobacterium tumefaciens- mediated gene transfer. Six- day- old cotyledons were co- cultivated with Agrobacterium cultures carrying binary vectors with two different genetic constructs. The first construct contained the beta- glucuronidase gene ( GUS) under the control of the cauliflower mosaic virus 35S promoter ( CaMV 35S), while the second construct contained the ethylene mutant receptor etr1- 1, which confers ethylene insensitivity, under the control of a leaf senescence- specific promoter ( sag12). Tissues co- cultivated with the GUS construct showed strong regeneration potential with over 90% of explants developing callus masses and 85% of the calli developing shoots. Histochemical GUS assays showed that 85.7% of the plants recovered were transgenic. Very different results were observed when cotyledon explants were co- cultivated with Agrobacteria carrying the etr1- 1 gene. There was a dramatic effect on the regeneration properties of the cultured explants with root formation taking place directly from the cotyledon tissue in 34% of the explants and no callus or shoots observed initially. Eventually callus formed in 10% of cotyledons and some organogenic shoots were obtained ( 2.86%). These results indicate that the ethylene insensitivity conferred by the etr1- 1 gene alters the normal pattern of regeneration in lettuce cotyledons, inhibiting the formation of shoots and stimulating root formation during regeneration.

Identification of functional sequences in the pregenomic RNA promoter of the Banana streak virus Cavendish strain (BSV-Cav)

The promoter regions of plant pararetroviruses direct transcription of the full-length viral genome into a pregenomic RNA that is an intermediate in the replication of the virus. It serves as template for reverse transcription and as polycistronic mRNA for translation to viral proteins. We have identified functional promoter elements in the intergenic region of the Cavendish isolate of Banana streak virus (BSV-Cav), a member of the genus Badnavirus. Potential binding sites for plant transcription factors were found both upstream and downstream of the transcription start site by homology search in the PLACE database of plant cis-acting elements. The functionality of these putative cis-acting elements was tested by constructing loss-of-function and regain-of-function mutant promoters whose activity was quantified in embryogenic sugarcane suspension cells. Four regions that are important for activity of the BSV-Cav promoter were identified: the region containing an as-l-like element, the region around-141 and down to -77, containing several putative transcription factor binding sites, the region including the CAAT-box, and the leader region. The results could help explain the high BSV-Cav promoter activity that was observed previously in transgenic sugarcane plants and give more insight into the plant cell-mediated replication of the viral genome in banana streak disease. (C) 2004 Elsevier B.V. All rights reserved.

Repressor- and activator-type ethylene response factors functioning in jasmonate signaling and disease resistance identified via a genome-wide screen of Arabidopsis transcription factor gene expression

To identify transcription factors (TFs) involved in jasmonate (JA) signaling and plant defense, we screened 1,534 Arabidopsis (Arabidopsis thaliana) TFs by real-time quantitative reverse transcription-PCR for their altered transcript at 6 h following either methyl JA treatment or inoculation with the incompatible pathogen Alternaria brassicicola. We identified 134 TFs that showed a significant change in expression, including many APETALA2/ethylene response factor (AP2/ERF), MYB, WRKY, and NACTF genes with unknown functions. Twenty TF genes were induced by both the pathogen and methyl JA and these included 10 members of the AP2/ERF TF family, primarily from the B1a and B3 subclusters. Functional analysis of the B1a TF AtERF4 revealed that AtERF4 acts as a novel negative regulator of JA-responsive defense gene expression and resistance to the necrotrophic fungal pathogen Fusarium oxysporum and antagonizes JA inhibition of root elongation. In contrast, functional analysis of the B3 TF AtERF2 showed that AtERF2 is a positive regulator of JA-responsive defense genes and resistance to F. oxysporum and enhances JA inhibition of root elongation. Our results suggest that plants coordinately express multiple repressor-and activator-type AP2/ERFs during pathogen challenge to modulate defense gene expression and disease resistance.

Histological structure of the cancellous bone layer in Bothriolepis canadensis (Antiarchi, Placodermi)

The Placodermi are extinct basal gnathostomes which had extensive dermal and perichondral bone, but which lacked the endochondral bone which characterizes the more derived bony fishes. Thin sections of bone from a specimen of the antiarch placoderm Bothriolepis canadensis, from the Escuminac Formation ( Frasnian, Upper Devonian), Quebec, Canada, reveal that part of the cancellous layer in its dermal and endoskeletal bone formed from perichondral bone trabeculae growing around cartilage spheres. The resultant structure mimics that of osteichthyan endochondral bone. The layout and dimensions of this polygonal mosaic patterning of the bone trabeculae and flattened cartilage spheres resemble those of the prismatic layers of calcified cartilage in chondrichthyans. If the lack of endoskeletal bone in chondrichthyans is a derived character, then the structure identified in B. canadensis could represent a 'template' for the formation of prismatic calcified cartilage in the absence of bone.

Reinforcement drives rapid allopatric speciation

Allopatric speciation results from geographic isolation between populations. In the absence of gene flow, reproductive isolation arises gradually and incidentally as a result of mutation, genetic drift and the indirect effects of natural selection driving local adaptation(1-3). In contrast, speciation by reinforcement is driven directly by natural selection against maladaptive hybridization(1,4). This gives individuals that choose the traits of their own lineage greater fitness, potentially leading to rapid speciation between the lineages(1,4). Reinforcing natural selection on a population of one of the lineages in a mosaic contact zone could also result in divergence of the population from the allopatric range of its own lineage outside the zone(4-6). Here we test this with molecular data, experimental crosses, field measurements and mate choice experiments in a mosaic contact zone between two lineages of a rainforest frog. We show that reinforcing natural selection has resulted in significant premating isolation of a population in the contact zone not only from the other lineage but also, incidentally, from the closely related main range of its own lineage. Thus we show the potential for reinforcement to drive rapid allopatric speciation.

Integrating JERS-1 imaging radar and elevation models for mapping tropical rainforest communities in far North Queensland, Australia

The Wet Tropics World Heritage Area in Far North Queens- land, Australia consists predominantly of tropical rainforest and wet sclerophyll forest in areas of variable relief. Previous maps of vegetation communities in the area were produced by a labor-intensive combination of field survey and air-photo interpretation. Thus,. the aim of this work was to develop a new vegetation mapping method based on imaging radar that incorporates topographical corrections, which could be repeated frequently, and which would reduce the need for detailed field assessments and associated costs. The method employed G topographic correction and mapping procedure that was developed to enable vegetation structural classes to be mapped from satellite imaging radar. Eight JERS-1 scenes covering the Wet Tropics area for 1996 were acquired from NASDA under the auspices of the Global Rainforest Mapping Project. JERS scenes were geometrically corrected for topographic distortion using an 80 m DEM and a combination of polynomial warping and radar viewing geometry modeling. An image mosaic was created to cover the Wet Tropics region, and a new technique for image smoothing was applied to the JERS texture bonds and DEM before a Maximum Likelihood classification was applied to identify major land-cover and vegetation communities. Despite these efforts, dominant vegetation community classes could only be classified to low levels of accuracy (57.5 percent) which were partly explained by the significantly larger pixel size of the DEM in comparison to the JERS image (12.5 m). In addition, the spatial and floristic detail contained in the classes of the original validation maps were much finer than the JERS classification product was able to distinguish. In comparison to field and aerial photo-based approaches for mapping the vegetation of the Wet Tropics, appropriately corrected SAR data provides a more regional scale, all-weather mapping technique for broader vegetation classes. Further work is required to establish an appropriate combination of imaging radar with elevation data and other environmental surrogates to accurately map vegetation communities across the entire Wet Tropics.

Characterization of a strong, constitutive mung bean (Vigna radiata L.) promoter with a complex mode of regulation in planta

We report the cloning and characterization in tobacco and Arabidopsis of a Vigna radiata L. (mung bean) promoter that controls the expression of VR-ACS1, an auxin-inducible ACC synthase gene. The VR-ACS1 promoter exhibits a very unusual behavior when studied in plants different from its original host, mung bean. GUS and luciferase in situ assays of transgenic plants containing VR-ACS1 promoter fusions show strong constitutive reporter gene expression throughout tobacco and Arabidopsis development. In vitro quantitative analyses show that transgenic plants harboring VR-ACS1 promoter-reporter constructs have on average 4-6 fold higher protein and activity levels of both reporter genes than plants transformed with comparable CaMV 35S promoter fusions. Similar transcript levels are present in VR-ACS1 and CaMV 35S promoter lines, suggesting that the high levels of gene product observed for the VR-ACS1 promoter are the combined result of transcriptional and translational activation. All tested deletion constructs retaining the core promoter region can drive strong constitutive promoter activity in transgenic plants. This is in contrast to mung bean, where expression of the native VR-ACS1 gene is almost undetectable in plants grown under normal conditions, but is rapidly and highly induced by a variety of stimuli. The constitutive behavior of the VR-ACS1 promoter in heterologous hosts is surprising, suggesting that the control mechanisms active in mung bean are impaired in tobacco and Arabidopsis. The 'aberrant' behavior of the VR-ACS1 promoter is further emphasized by its failure to respond to auxin and cycloheximide in heterologous hosts. VR-ACS1 promoter regulatory mechanisms seem to be different from all previously characterized auxin-inducible promoters.