J. Desair

Nucleotide sequence of the T-DNA region encoding transcripts 6a and 6b of the pTiT37 nopaline Ti plasmid.

SummaryThe nucleotide sequence of the T-DNA region encoding transcripts 6a and 6b of the pTiT37 nopaline Ti plasmid has been determined. Analysis of this sequence allowed us to find two open reading frames in opposite orientation and separated by 482 bp. Comparison with previous published nucleotide sequences of the homologous regions of the pTiAch5 and the pTi15955 octopine Ti plasmids reveals that the coding sequences as well as the 5′- and 3′ 3-untranslated regions of both genes are highly homologous.

Identification of insertion sequence element IS427 in pTiT37 plasmid DNA of an Agrobacterium tumefaciens T37 isolate

The isolation and characterization of an insertion sequence (IS) element, IS427, from Agrobacterium tumefaciens T37 is described. IS427 is present in three nonidentical copies on the pTiT37 plasmid. The copy that was isolated through transposition on the entrapment vector pUCD800 contains at its ends a 16-bp imperfect inverted repeat and generates a 2-bp duplication of the target DNA. IS427 does not show homology with previously characterized IS elements of A. tumefaciens, based on hybridization experiments and/or sequence comparison.

Azospirillum-Plant Root Associations: Genetics of IAA Biosynthesis and Plant Cell Wall Degradation

The genus Azospirillum comprises free-living N2 fixing rhizosphere bacteria that have been isolated from different soil types and from the roots of numerous wild and cultivated plants all over the world. Field trials, carried out at different locations, have demonstrated that under certain environmental and soil conditions, inoculation with Azospirillum has beneficial effects on plant yields. Bacterial phytohormone biosynthesis has often been proposed as being responsible for the observed plant growth promotion upon Azospirillum inoculation.

Crystallization and preliminary X-ray diffraction analysis of a novel pectate lyase from Azospirillum irakense

The PelA gene from the N(2)-fixing plant-associated bacterium Azospirillum irakense encodes a pectate lyase. Analysis of the corresponding amino-acid sequence revealed no homology to other bacterial, plant and fungal pectinases of known published structure, resulting in the classification of the enzyme in a new pectate lyase family. The A. irakense PelA has been crystallized using the hanging-drop vapour-diffusion method at 277 K. The crystals are hexagonal, with unit-cell parameters a = b = 85.55, c = 230.13 A, gamma = 120 degrees, and belong to space group P6(5)22 or P6(1)22, having one molecule per asymmetric unit. Diffraction data to a resolution of 1.97 A were collected at synchrotron facilities, as well as a three-wavelength MAD data set from an Hg-derivative crystal to a resolution of 2.6 A.

Structure of a novel pectate lyase from Azospirillum irakense

Pectate lyases are the major pectinases that play a key role in the development of the soft-rot disease. Besides in phytopathogens, pectin depolymerization has also been reported in non-pathogenic plant associated bacteria such as the N2fixing endosymbiont Rhizobium and the N2-fixing soil bacterium Azospirillum irakense. A gene from A. irakense encoding a pectate lyase (termed PelA) was isolated by heterologous expression of the gene in Escherichia coli . Analysis of the corresponding amino acid sequence revealed no homology to other bacterial, plant and fungal pectinases leading to the classification of the enzyme in a new pectate lyase family (family 10). The A. irakense PelA has been crystallized using the hanging-drop vapor diffusion method at 277K. These crystals are hexagonal with cell dimensions of a = b = 85.55 Å, c = 230.13 Å, γ = 120°, and space group P6522 having one molecule per asymmetric unit2. Diffraction data to a resolution of 1.97 Å were collected at synchrotron facilities, as well as a three-wavelengths MAD data set on a Hg derivate crystal to a resolution of 2.6 Å. The preliminary structural results show that PelA does not have the characteristic parallel β-helix fold of the polysaccharide pectate lyase families. References 1. Bekri, M.A., Desair, J., Keijers, V., Proost, P., Searle-van Leeuwen, M., Vanderleyden, J. & VandeBroeck, A. (1999). J. Bacteriol. 181, 2440-2447. 2. Novoa de Armas, H., Rabijns A., Verboven C., Desair, J., Vande Broek, A., Vanderleyden, J., De Ranter, C. (2002). Acta Cryst. D58, 292-295.

Evidence for a Physiological Role of IAA in Azospirillum brasilense Sp245

Regarding direct plant growth promotion, the ability of Azospirillum brasilense to produce indole-3-acetic acid (IAA) is now intensively studied. IAA biosynthesis in A. brasilense proved to be surprisingly complex, since at least three biosynthetic pathways are present (Prinsen et al, 1993). For one biosynthesis pathway, we have cloned and sequenced the A. brasilense ipdC gene, encoding the indole-3-pyruvic acid decarboxylase (Costacurta et al, 1994).