Fortunella margarita Transcriptional Reprogramming Triggered by Xanthomonas citri subsp. citri

<p>Abstract</p> <p>Background</p> <p>Citrus canker disease caused by the bacterial pathogen <it>Xanthomonas citri </it>subsp. <it>citri (</it>Xcc) <it>has </it>become endemic in areas where high temperature, rain, humidity, and windy conditions provide a favourable environment for the dissemination of the bacterium. Xcc is pathogenic on many commercial citrus varieties but appears to elicit an incompatible reaction on the citrus relative <it>Fortunella margarita </it>Swing (kumquat), in the form of a very distinct delayed necrotic response. We have developed subtractive libraries enriched in sequences expressed in kumquat leaves during both early and late stages of the disease. The isolated differentially expressed transcripts were subsequently sequenced. Our results demonstrate how the use of microarray expression profiling can help assign roles to previously uncharacterized genes and elucidate plant pathogenesis-response related mechanisms. This can be considered to be a case study in a citrus relative where high throughput technologies were utilized to understand defence mechanisms in <it>Fortunella </it>and citrus at the molecular level.</p> <p>Results</p> <p><b>cDNAs from sequenced kumquat libraries (ESTs) made from subtracted RNA populations, healthy vs. infected, were used to make this microarray</b>. Of 2054 selected genes on a customized array, 317 were differentially expressed (P < 0.05) in Xcc challenged kumquat plants compared to mock-inoculated ones. This study identified components of the incompatible interaction such as reactive oxygen species (ROS) and programmed cell death (PCD). Common defence mechanisms and a number of resistance genes were also identified. In addition, there were a considerable number of differentially regulated genes that had no homologues in the databases. This could be an indication of either a specialized set of genes employed by kumquat in response to canker disease or new defence mechanisms in citrus.</p> <p>Conclusion</p> <p>Functional categorization of kumquat Xcc-responsive genes revealed an enhanced defence-related metabolism as well as a number of resistant response-specific genes in the kumquat transcriptome in response to Xcc inoculation. Gene expression profile(s) were analyzed to assemble a comprehensive and inclusive image of the molecular interaction in the kumquat/Xcc system. This was done in order to elucidate molecular mechanisms associated with the development of the hypersensitive response phenotype in kumquat leaves. These data will be used to perform comparisons among citrus species to evaluate means to enhance the host immune responses against bacterial diseases.</p

Cloning, localization and expression analysis of vacuolar sugar transporters in the CAM plant Ananas comosus (pineapple).

In photosynthetic tissues of the CAM plant pineapple (Ananas comosus), storage of soluble sugars in the central vacuole during the daytime and their remobilization at night is required to provide carbon skeletons for nocturnal CO(2) fixation. However, soluble sugars produced photosynthetically must also be exported to support growth processes in heterotrophic tissues. To begin to address how vacuolar sugar storage and assimilate partitioning are regulated in A. comosus, degenerate PCR and cDNA library screening were used to clone three candidate sugar transporters from the leaves of this species. Subcellular localization of the three transporters was investigated via expression of YFP-fusion proteins in tobacco epidermal cells and their co-localization with subcellular markers by confocal microscopy. Using this strategy, a putative hexose transporter (AcMST1) and a putative inositol transporter (AcINT1) were identified that both localized to the tonoplast, whereas a putative sucrose transporter (AcSUT1) was found to localize to prevacuolar compartments. A cDNA (AcMST2) with high similarity to a recently characterized tonoplast hexose transporter in Arabidopsis was also identified from an A. comosus fruit EST database. Analyses of transcript abundance indicated that AcMST1 was more highly expressed in fruits compared to leaves of A. comosus, whilst transcripts of AcINT1, AcSUT1, and AcMST2 were more abundant in leaves. Transcript abundance of AcINT1, the putative inositol transporter, showed day-night changes comparable to those of other CAM-related transcripts described in Mesembryanthemum crystallinum. The results are discussed in terms of the role of vacuolar sugar transporters in regulating carbon flow during the diel cycle in CAM plants

A class of cell wall-derived damage-associated molecular patterns affects plant-aphid interactions

Aphids are among the most destructive pests in agriculture, causing direct damage to crops by feeding on phloem, as well as indirect losses by transmitting more than half of all described plant viruses. During feeding aphids secrete effector proteins into their hosts to manipulate cellular processes and promote infestation. Aphids are largely controlled by pesticides that are environmentally damaging and are being withdrawn from the market. The development of insect-resistant crops represents a viable alternative for aphid control and can be greatly enhanced by knowledge on plant resistance mechanisms against these pests. Cell wall and cell wall-derived oligogalacturonides (OGs), a well-known class of damage-associated molecular patterns (DAMPs), are important components of the plant immune system against fungal and bacterial pathogens, but their role against aphids is unknown. We show that OGs enhance Arabidopsis thaliana resistance to the green peach aphid Myzus persicae. This resistance response is mediated by calcium-dependent protein kinases. Intriguingly, the aphid effector Mp10 suppresses the OG-induced immunity. A. thaliana transgenic plants with increased methyl esterification level of cell wall pectin are more susceptible to aphid colonisation. Our work shows that cell walls and OGs are components of the plant immune response to aphids. This is important, because aphids are likely to release these DAMPs when they penetrate plant cell walls with their stylets. Author

Clinical effectiveness and cost-effectiveness of bone morphongenetic proteins in the non-healing of fractures and spinal fusion: a systematic review

Objectives: To assess the clinical effectiveness and cost-effectiveness of bone morphogenetic protein (BMP) for the treatment of spinal fusions and the healing of fractures compared with the current standards of care. Data sources: Electronic databases, related journals and references from identified studies were searched in January 2006, with an updated search only for randomised controlled trials (RCTs) in November 2006. Review methods: A systematic review of available data was conducted. The data from selected studies were then analysed and graded according to quality and processed to give a value to the efficacy of BMP. Existing models were modified or updated to evaluate the cost-effectiveness of BMP for open tibial fractures and spinal fusion. Results: All selected trials were found to have several methodological weaknesses. Insufficient sample size in most trials, meant that patient baseline comparability between trial arms was not achieved and the statistical power to detect a moderate effect was low. Data did indicate that BMP increased fracture union among patients with acute tibial fractures and found that high-dose BMP is more effective than a lower dose for open tibial fractures. The healing rate in the BMP group was not found to be statistically significantly different from that in the autogenous bone grafting group for patients with tibial non-union fractures, but BMP reduced the number of secondary interventions in patients with acute tibial fractures compared with controls. There was very limited evidence that BMP in scaphoid non-union was safe and may help to accelerate non-union healing when used in conjunction with either autograft or allograft. There was evidence that BMP-2 is more effective than autogenous bone graft for radiographic fusion in patients with single-level degenerative disc disease. No significant difference was found when BMP-7 was compared with autograft for degenerative spondylolisthesis with spinal stenosis and spondylolysis. The use of BMP was associated with a reduced operating time, improvement in clinical outcomes and a shorter hospital stay as compared with autograft. The proportion of secondary interventions tended to be lower in the BMP group than the control, but not of statistical significance. Trial data on time to return to work postoperatively were sometimes difficult to interpret because of unclear or inappropriate data analysis methods. The incremental cost of BMP for open tibial fractures was estimated to be about £3.5 million per year in the UK. The estimated incremental cost per quality-adjusted life-year (QALY) gained is £32,603. The probability that cost per QALY gained is less than £30,000 for open tibial fracture is 35.5%. The cost-effectiveness ratio is sensitive to tho price of BMP and the severity of open tibial fractures. The use of recombinant human bone mor phogenetic protein for spinal fusion surgery may increase the cost to the UK N HS by about £1.3 million per year. The estimated incremental cost per QALY gained was about £120,390. The probability that BMP is cost-effective (i.e. cost/ QALY less than £30,000) was only 6.4%. From the societal perspective, the estimated total cost of using BMP for spinal fusion is about £4.2 million per year in the UK. Conclusions: Additional BMP treatment plus conventional intervention is more effective than conventional intervention alone for union of acute open tibial fractures. The cost-effectiveness of additional BMP may be improved if the price of BMP is reduced or if BMP is mainly used in severe cases. BMP may eliminate the need for autogenous bone grafting so that costs and complications related to harvesting autograft can be avoided. In non-unions, there is no evidence that BMP is more or less effective than bone graft; however, it is currently used when bone graft and other treatments have failed. The use of BMP-2 in spinal fusion surgery seems to be more effective than autogenous bone graft in terms of radiographic spinal fusion among patients with single-level degenerative disc disease. There is a lack of evidence about the effectiveness of BMP for other spinal disorders including spondylolisthesis and spinal stenosis. There was limited evidence showing that BMP is associated with greater improvement in clinical outcomes. According to the results of economic evaluation, the use of BMP for spinal fusion is unlikely to be cost-effective. The following areas would benefit from further research: clinical trials of BMP that include formal economic evaluation, a multicentre RCT of fracture non-union and of interbody and/or posterolateral spinal fusion, trials of non-tibial acute long bone fractures, and RCTs comparing BMP-2, BMP-7 and controls. © Queen's Printer and Controller of HMSO 2007. All rights reserved