Novel mechanisms of resistance to Plum pox virus are being unravelled in the model plant, Arabidopsis thaliana

International audienc

Single amino acid changes in the turnip mosaic virus viral genome-linked protein (VPg) confer virulence towards Arabidopsis thaliana mutants knocked out for eukaryotic initiation factors eIF(iso)4E and eIF(iso)4G

Previous resistance analyses of Arabidopsis thaliana mutants knocked out for eukaryotic translation initiation factors showed that disruption of the At-eIF(iso)4E or both the At-eIF(iso)4G1 and At-eIF(iso)4G2 genes resulted in resistance against turnip mosaic virus (TuMV). This study selected TuMV virulent variants that overcame this resistance and showed that two independent mutations in the region coding for the viral genome-linked protein (VPg) were sufficient to restore TuMV virulence in At-eIF(iso)4E and At-eIF(iso)4G1xAt-eIF(iso)4G2 knockout plants. As a VPg-eIF(iso)4E interaction has been shown previously to be critical for TuMV infection, a systematic analysis of the interactions between A. thaliana eIF4Es and VPgs of virulent and avirulent TuMVs was performed. The results suggest that virulent TuMV variants may use an eIF4F-independent pathway. © 2010 SGM

[PP. 27.24] DIAGNOSTIC ACCURACY AND DIAGNOSTIC GAIN OF CRITERIA TO INTERPRET UNILATERALLY SELECTIVE ADRENAL VEIN SAMPLING (AVS) RESULTS

Objective: 10–20% of AVS performed in Excellence centers for primary aldosteronism (PA) are not bilaterally selective. The ratio of cortisol-corrected aldosterone concentration between adrenal vein and inferior vena cava (unilateral ratio, UR) has been proposed to interpret unilaterally selective AVS [1]:UR<0.5could suggest unilateral PA on the opposite side; UR >5.5 could suggest unilateral PA on the same side, and UR 0.5–5.5 would be inconclusive. Design and method: This retrospective study evaluates the diagnostic value of the UR on AVS data collected over10 years in a referral centre. French AVS-consensus criteria (selectivity index >2, lateralisation ratio >4) were used for AVS interpretation. We first assessed the numbers of cases with left and right UR both <0.5 or both >5.5, because in these cases the interpretation of unilaterally selective AVS will depend only on the side of successful adrenal vein cannulation, not on the side of the disease. We then assessed the sensitivity, specificity and PPV of these criteria for the diagnosis of unilateral PA. Cases with left and right UR both <0.5 or both >5.5 were counted as false positives for these calculations. We finally assessed the diagnostic impact of using the unilateral criteria in case of unilaterally selective AVS. Results: -537AVS were performed from 2001–2010, 64(12%) were not bilaterally selective using the reference criteria (28unilaterally selective and 36 bilaterally non-selective), 287 (53%) were diagnostic of bilateral PA, 99 (18%) of left PA and 87 (16%) of right PA [Table 1]. -Among 473 bilaterally selective AVS, 7 (1.5%) had left and right UR both <0.5 and 32 (7%) had left and right UR both >5.5 [Table 2]. -Sensitivity of UR <0.5 to detect unilateral PA was 55%, specificity 91%, PPV79%. -Sensitivity of UR >5.5 was 51%, specificity71%, PPV53% [Table3]. -Using these criteria to interpret 28 unilaterally selective AVS led to diagnose 2right PA but 0left PA with a contralateral UR <0.5, 10 right PA and 6left PA with an ipsilateral UR >5.5, the remaining 10 cases staying inconclusive. However, among the 16 unilateral PA diagnosed with an ipsilateral UR >5.5, we must expect 8 false positives

Allelic variation at the rpv1 locus controls partial resistance to Plum pox virus infection in Arabidopsis thaliana

Sharka is caused by Plum pox virus (PPV) in stone fruit trees. In orchards, the virus is transmitted by aphids and by grafting. In Arabidopsis, PPV is transferred by mechanical inoculation, by biolistics and by agroinoculation with infectious cDNA clones. Partial resistance to PPV has been observed in the Cvi-1 and Col-0 Arabidopsis accessions and is characterized by a tendency to escape systemic infection. Indeed, only one third of the plants are infected following inoculation, in comparison with the susceptible Ler accession. Genetic analysis showed this partial resistance to be monogenic or digenic depending on the allelic configuration and recessive. It is detected when inoculating mechanically but is overcome when using biolistic or agroinoculation. A genome-wide association analysis was performed using multiparental lines and 147 Arabidopsis accessions. It identified a major genomic region, rpv1. Fine mapping led to the positioning of rpv1 to a 200 kb interval on the long arm of chromosome 1. A candidate gene approach identified the chloroplast phosphoglycerate kinase (cPGK2) as a potential gene underlying the resistance. A virus-induced gene silencing strategy was used to knock-down cPGK2 expression, resulting in drastically reduced PPV accumulation. These results indicate that rpv1 resistance to PPV carried by the Cvi-1 and Col-0 accessions is linked to allelic variations at the Arabidopsis cPGK2 locus, leading to incomplete, compatible interaction with the virus.Sharka Containmen

An antibody produced in tobacco expressing a hybrid β-1,4-galactosyltransferase is essentially devoid of plant carbohydrate epitopes

N-glycosylation of a mAb may have a major impact on its therapeutic merits. Here, we demonstrate that expression of a hybrid enzyme (called xylGalT), consisting of the N-terminal domain of Arabidopsis thaliana xylosyltransferase and the catalytic domain of human β-1,4-galactosyltransferase I (GalT), in tobacco causes a sharp reduction of N-glycans with potentially immunogenic core-bound xylose (Xyl) and fucose (Fuc) residues as shown by Western blot and MALDI-TOF MS analysis. A radioallergosorbent test inhibition assay with proteins purified from leaves of WT and these transgenic tobacco plants using sera from allergic patients suggests a significant reduction of potential immunogenicity of xylGalT proteins. A mAb purified from leaves of plants expressing xylGalT displayed an N-glycan profile that featured high levels of galactose, undetectable xylose, and a trace of fucose. Hence, a transgenic plant expressing the hybrid GalT might yield more effective and safer monoclonals for therapeutic purposes than WT plants and even transgenic plants expressing the unchanged GalT

Selective use of adrenal venous sampling in the lateralization of aldosterone-producing adenomas

It has been suggested that routine adrenal venous sampling (AVS) is necessary to lateralize an aldosterone-producing adenoma in patients with primary hyperaldosteronism. However, the success rate of AVS is variable, with potential risks. We review our experience at University of California San Francisco (UCSF), where AVS is used only selectively, to determine outcomes with this approach