Skip to main content
European Commission logo print header
Inhalt archiviert am 2022-12-23

Genetic and physical mapping of the I2 locus

Ziel

- To develop and apply reverse genetic and megabase cloning technologies in tomato with the final goal of physically isolating the I2 locus, a gene of dominant character that encodes resistance to Fusarium wilt disease;
- One main focus was to provide a high resolution map in the context of the I2 locus that could be used a platform to launch a map-based cloning project.

- Fusarium wilt is an economically important disease of tomatoes, caused by the soil-born fungus Fusarium oxysporum f. sp. lycopersici. There are three host-specific races of this pathogen. The dominant tomato gene I2 confers resistance to race 2. The I2 Fusarium resistance gene was mapped genetically to chromosome 11 of tomato, between the RFLP markers TG105 and TG36, 0.4 centiMorgan (cM) from TG105 (1). A mean value of 43 kb for each cM was assigned in the vicinity of I2. We have generated new RFLP markers in the region by chromosome walking from TG105 towards I2 on lambda clones, and by subcloning a 350 kb long YAC clone (YAC 8) (2) that contains TG105. These RLFP markers were mapped physically on YAC 8 by PFGE. High resolution was carried out on special populations and sets the stage for final cloning of the I2 locus (3).
- A cDNA clone, D14, that was isolated by YAC 8, turned out to be 53% similar to xanthine dehydrogenase from mammals and flies. Antibodies rose against a part of the protein encoded by D14 recognise cross reacting material of MW 80 kD, that is highly enriched in nodules of legumes, and seems to be induced by various environmental and pathogenic stress conditions.

Follow up

- Aldehyde oxidase (AO) and xanthine dehydrogenase (XD) are a group of ubiquitous hydroxylases, containing a Molybdenum cofactor (MoCo) and two iron sulphur groups. Plant AO and XD activities are involved in nitrogen metabolism and hormone biosynthesis, and their corresponding genes have not yet been isolated. Here we describe a new gene from tomato, which shows the characteristics of a MoCo containing hydroxylase (4). It shares sequence homology with xanthine dehydrogenases and aldehyde oxidases from various organisms, and similarly contains binding sites for two iron-sulphur centres and a molybdenum binding region. However, it does not contain the XD conserved sequences thought to be involved in NAD binding and in substrate specificity, and is likely to encode an AO-type activity. This gene was designated tomato aldehyde oxidase 1 (TAO1). TAO1 belongs to a multigene family, whose members are shown to map to clusters on chromosomes 1 and 11. MoCo hydroxylase activity is shown to be recognised by antibodies rose against recombinant TAO1 polypeptides. Immunoblots reveal that TAO1 cross reacting material is ubiquitously expressed in various organisms, and in plants it is mostly abundant in fruits and rapidly dividing tissues;

- Members of a new multigen family, complex I2C, were isolated by map-based cloning from the I2 F.o. f sp lycopersici race 2 resistance locus (5). The genes show structural similarity to the group of recently isolated resistance genes that contain a nucleotide binding motif and leucine rich repeats. Importantly, the presence of I2C antisense transgenes abrogated race 2 but not race 1 resistance in otherwise normal plants. Expression of the complete sense I2C-1 transgene conferred significant but partial resistance to F.o. f sp lycopersici race 2. All members of the I2C gene family have been mapped genetically and are dispersed on three different chromosomes. Some of the I2C members cosegregate with other tomato resistance loci. Comparison within the leucine-rich repeated region of I2C gene family members shows that they differ from each other mainly by insertions or deletions.

Thema/Themen

Data not available

Aufforderung zur Vorschlagseinreichung

Data not available

Koordinator

WAGENINGEN UNIVERSITY
EU-Beitrag
Keine Daten
Adresse
3,Dreijenlaan 3
6703 HA WAGENINGEN
Niederlande

Auf der Karte ansehen

Gesamtkosten
Keine Daten