Characterization of Aster Yellows in Oklahoma

Aster yellows (AY), caused by mycoplasma-like organisms (MLOs), was investigated in this study. Natural AY incidence in carrot and lettuce was recorded in three different locations in Oklahoma. MLO isolates from carrot, lettuce and daisy fleabane were collected and characterized. A trispecific polyclonal serum, produced against an AY MLO isolate from Oklahoma carrot, was used in serological detection of AY in different host sources. Selected wheat and peanut cultivars were screened for susceptibility to Oklahoma AY MLO.Plant Patholog

Prunus domestica Pathogenesis-Related Protein-5 Activates the Defense Response Pathway and Enhances the Resistance to Fungal Infection

Pathogenesis-related protein-5 (PR-5) has been implicated in plant disease resistance and its antifungal activity has been demonstrated in some fruit species. However, their roles, especially their interactions with the other defense responses in plant cells, are still not fully understood. In this study, we have cloned and characterized a new PR-5 cDNA named PdPR5-1 from the European plum (Prunus domestica). Expression of PdPR5-1 was studied in different cultivars varying in resistance to the brown rot disease caused by the necrotrophic fungus Monilinia fructicola. In addition transgenic Arabidopsis, ectopically expressing PdPR5-1 was used to study its role in other plant defense responses after fungal infection. We show that the resistant cultivars exhibited much higher levels of transcripts than the susceptible cultivars during fruit ripening. However, significant rise in the transcript levels after infection with M. fructicola was observed in the susceptible cultivars too. Transgenic Arabidopsis plants exhibited more resistance to Alternaria brassicicola. Further, there was a significant increase in the transcripts of genes involved in the phenylpropanoid biosynthesis pathway such as phenylalanine ammonia-lyase (PAL) and phytoalexin (camalexin) pathway leading to an increase in camalexin content after fungal infection. Our results show that PdPR5-1 gene, in addition to its anti-fungal properties, has a possible role in activating other defense pathways, including phytoalexin production

Bacterial survival and mineralization of p-nitrophenol in soil by green fluorescent protein-marked Moraxella sp. G21 encapsulated cells

International audienceMoraxella sp. G21 cells marked with the green fluorescent protein (gfp) survived in κ-carrageenan beads and as free cells for a month after inoculation into autoclaved soil and non-sterile soil contaminated with p-nitrophenol (PNP). Similar [U-14C]PNP mineralization values were produced by encapsulated Moraxella sp. G21 cells and as free cells (53 and 60% mineralization). There was no significant difference between cell survival and [U-14C]PNP mineralization activity in soil by the rifampicin-resistant Moraxella sp. mental strain and Moraxella sp. G21. The ability of encapsulated Moraxella sp. G21 cells to survive, retain their green fluorescence and mineralize [U-14C]PNP suggests that the GFP-marked strain encapsulated in κ-carrageenan may be useful for bioremediation of toxic chemicals in soil

Mineralization of p-nitrophenol by pentachlorophenol-degrading Sphingomonas spp.

International audiencePentachlorophenol-degrading Sphingomonas sp. UG30 and Sphingomonas chlorophenolica strains RA2 and ATCC 39723 can transform p-nitrophenol in either mineral salts-glutamate or mineral salts-glucose medium after an initial lag period. However, mineralization of p-nitrophenol by these bacterial strains was observed only in mineral salts-glucose medium. When p-nitrophenol was the sole nitrogen source in the growth medium, UG30 mineralized 32% of 140 mM [14C]p-nitrophenol which was 10% higher than the amount of [14C]p-nitrophenol mineralized in mineral salts-glucose medium. UG30 did not transform or mineralize p-nitrophenol (in a growth medium) in the absence of glucose or glutamate. All three strains released nitrite during p-nitrophenol degradation in mineral salts-glucose medium and mineral salts-glutamate medium. The transformation rate of p-nitrophenol by UG30 was dependent on the initial p-nitrophenol concentration, with the optimal rate being found at 310 μM of p-nitrophenol and inhibition observed at ≥1100 μM of p-nitrophenol. Pre-exposure of UG30 cells to p-nitrophenol eliminated the initial lag phase of p-nitrophenol transformation. However, pre-growth of UG30 cells on pentachlorophenol did not reduce the lag period for p-nitrophenol transformation. Both p-nitrophenol- and pentachlorophenol-induced UG30 cells degraded pentachlorophenol without any lag phase. Thin layer chromatographic analysis of the reaction mixture suggested 4-nitrocatechol was an intermediate of p-nitrophenol transformation by UG30

Green fluorescent protein as a visual marker in ap-nitrophenol degradingMoraxellasp.

International audienceThe green fluorescent protein gene (gfp) was introduced into a p-nitrophenol-metabolizing strain of Moraxella sp. by chromosomal integration. The gfp-marked transformants, designated Moraxella sp. strains G21 and G25, exhibited green fluorescence under UV light. Molecular characterization by PCR and Southern hybridization showed the presence of gfp in both transformants. Both transformants and the parent strain degraded 720 μM of p-nitrophenol with nitrite release within 4 h after inoculation in minimal medium supplemented with yeast extract. Transformants degraded up to 1440 μM p-nitrophenol and mineralized about 60% of 720 μM p-nitrophenol, both in broth and in soil, to the same extent as the parent strain. Insertion of gfp did not adversely affect the expression of p-nitrophenol-degrading genes in the transformants. Survival studies indicated that individual green fluorescent colonies of transformants can be detected up to 2 weeks after inoculation in soil. These marked strains could be of value in studies on microbial survival in the environment

Camalexin content in the leaves of transgenic <i>Arabidopsis</i> plants expressing the plum <i>PdPR5-1</i> gene.

<p>Leaves were collected three days after inoculation with <i>Alternaria brassicicola</i> from the wild type and three independent transgenic lines.</p

<i>PdPR5-1</i> promoter analysis using PLANT CARE website.

<p><i>PdPR5-1</i> promoter analysis using PLANT CARE website.</p

Multiple amino acid sequence alignments of <i>Prunus domestica</i> PR5; PdPR5-1 (HM853674) with the closely related sequences, <i>Malus domestica</i> Md2PR5 (AJ243427), <i>Prunus persica</i> PpPR5 (AAM00215.1), <i>Prunus avium</i> TLP_PRUAV (P50694.1), <i>Prunus pyrifolia</i> P.pyri (BAA28872.1), <i>Arabidopsis thaliana</i> AtPR5 (At1g75040) and <i>Vitis vinifera</i> VVTL-1 (AAB61590).

<p>Conserved residues are shaded in black. Dark grey shading indicates similar residues in six out of seven of the sequences, and light grey shading indicates similar residues in five out of seven of the sequences.</p

<i>PdPR5-1</i> promoter analysis using PLACE website.

<p><i>PdPR5-1</i> promoter analysis using PLACE website.</p