Autoactive alleles of the flax L6 rust resistance gene induce non-race-specific rust resistance associated with the hypersensitive response.

L6 is a nucleotide binding site-leucine rich repeat (NBS-LRR) gene that confers race-specific resistance in flax (Linum usitatissimum) to strains of flax rust (Melampsora lini) that carry avirulence alleles of the AvrL567 gene but not to rust strains that carry only the virulence allele. Several mutant and recombinant forms of L6 were made that altered either the methionine-histidine-aspartate (MHD) motif conserved in the NBS domain of resistance proteins or exchanged the short domain C-terminal to the LRR region that is highly variable among L allele products. In transgenic flax some of these alleles are autoactive; they cause a gene dosage-dependent dwarf phenotype and constitutive expression of genes that are markers for the plant defense response. Their effects and penetrance ranged from extreme to mild in their degree of plant stunting, survival, and reproduction. Dwarf plants were also resistant to flax rust strains virulent to wild-type L6 plants, and this nonspecific resistance was associated with a hypersensitive response (HR) at the site of rust infection. The strongest autoactive allele, expressed in Arabidopsis from an ethanol-inducible promoter, gave rise to plant death dependent on the enhanced disease susceptibility 1 (EDS1) gene, which indicates that the mutant flax (Linaceae) L6 gene can signal cell death through a defined disease-resistance pathway in a different plant family (Brassicaceae).

Gene expression profile changes in cotton root and hypocotyl tissues in response to infection with Fusarium oxysporum f. sp. vasinfectum.

Microarray analysis of large-scale temporal and tissue-specific plant gene expression changes occurring during a susceptible plant-pathogen interaction revealed different gene expression profile changes in cotton root and hypocotyl tissues. In hypocotyl tissues infected with Fusarium oxysporum f. sp. vasinfectum, increased expression of defense-related genes was observed, whereas few changes in the expression levels of defense-related genes were found in infected root tissues. In infected roots, more plant genes were repressed than were induced, especially at the earlier stages of infection. Although many known cotton defense responses were identified, including induction of pathogenesis-related genes and gossypol biosynthesis genes, potential new defense responses also were identified, such as the biosynthesis of lignans. Many of the stress-related gene responses were common to both tissues. The repression of drought-responsive proteins such as aquaporins in both roots and hypocotyls represents a previously unreported response of a host to pathogen attack that may be specific to vascular wilt diseases. Gene expression results implicated the phytohormones ethylene and auxin in the disease process. Biochemical analysis of hormone level changes supported this observation.

A putative ABC transporter confers durable resistance to multiple fungal pathogens in wheat.

Agricultural crops benefit from resistance to pathogens that endures over years and generations of both pest and crop. Durable disease resistance, which may be partial or complete, can be controlled by several genes. Some of the most devastating fungal pathogens in wheat are leaf rust, stripe rust, and powdery mildew. The wheat gene Lr34 has supported resistance to these pathogens for more than 50 years. Lr34 is now shared by wheat cultivars around the world. Here, we show that the LR34 protein resembles adenosine triphosphate-binding cassette transporters of the pleiotropic drug resistance subfamily. Alleles of Lr34 conferring resistance or susceptibility differ by three genetic polymorphisms. The Lr34 gene, which functions in the adult plant, stimulates senescence-like processes in the flag leaf tips and edges.

Fusarium wilt (Fusarium oxysporum f. sp. vasinfectum) genes expressed during infection of cotton (Gossypium hirsutum)dagger.

SUMMARY We sought to identify Fusarium oxysporum f. sp. vasinfectum (Fov) genes that may be associated with pathogenicity. Initially we utilized microarray and Q-PCR technology to identify Fov genes expressed in root and hypocotyl tissues during a compatible infection of cotton. We identified 218 fungal clones representing 174 Fov non-redundant genes as expressed in planta. The majority of the expressed sequences were expressed in infected roots, with only six genes detected in hypocotyl tissue. The Fov genes identified were predominately of unknown function or associated with fungal growth and energy production. We then analysed the expression of the identified fungal genes in infected roots and in saprophytically grown mycelia and identified 11 genes preferentially expressed in plant tissue. A putative oxidoreductase gene (with homology to AtsC) was found to be highly preferentially expressed in planta. In Agrobacterium tumefaciens, AtsC is associated with virulence. Inoculation of a susceptible and a partially resistant cotton cultivar with either a pathogenic or a non-pathogenic isolate of Fov revealed that the expression of the Fov AtsC homologue was associated with pathogenicity and disease symptom formation.

A global assembly of cotton ESTs.

Approximately 185,000 Gossypium EST sequences comprising >94,800,000 nucleotides were amassed from 30 cDNA libraries constructed from a variety of tissues and organs under a range of conditions, including drought stress and pathogen challenges. These libraries were derived from allopolyploid cotton (Gossypium hirsutum; A(T) and D(T) genomes) as well as its two diploid progenitors, Gossypium arboreum (A genome) and Gossypium raimondii (D genome). ESTs were assembled using the Program for Assembling and Viewing ESTs (PAVE), resulting in 22,030 contigs and 29,077 singletons (51,107 unigenes). Further comparisons among the singletons and contigs led to recognition of 33,665 exemplar sequences that represent a nonredundant set of putative Gossypium genes containing partial or full-length coding regions and usually one or two UTRs. The assembly, along with their UniProt BLASTX hits, GO annotation, and Pfam analysis results, are freely accessible as a public resource for cotton genomics. Because ESTs from diploid and allotetraploid Gossypium were combined in a single assembly, we were in many cases able to bioinformatically distinguish duplicated genes in allotetraploid cotton and assign them to either the A or D genome. The assembly and associated information provide a framework for future investigation of cotton functional and evolutionary genomics.