Gene silencing: plants and viruses fight it out.
Plants can become 'immune' to attack by viruses by degrading specific viral RNA, but some plant viruses have evolved the general capacity to suppress this resistance mechanism. (+info)
Characterization of an insertion sequence element associated with genetically diverse plant pathogenic Streptomyces spp.
Streptomycetes are common soil inhabitants, yet few described species are plant pathogens. While the pathogenicity mechanisms remain unclear, previous work identified a gene, nec1, which encodes a putative pathogenicity or virulence factor. nec1 and a neighboring transposase pseudogene, ORFtnp, are conserved among unrelated plant pathogens and absent from nonpathogens. The atypical GC content of nec1 suggests that it was acquired through horizontal transfer events. Our investigation of the genetic organization of regions adjacent to the 3' end of nec1 in Streptomyces scabies 84.34 identified a new insertion sequence (IS) element, IS1629, with homology to other IS elements from prokaryotic animal pathogens. IS1629 is 1,462 bp with 26-bp terminal inverted repeats and encodes a putative 431-amino-acid (aa) transposase. Transposition of IS1629 generates a 10-bp target site duplication. A 77-nucleotide (nt) sequence encompassing the start codon and upstream region of the transposase was identified which could function in the posttranscritpional regulation of transposase synthesis. A functional copy of IS1629 from S. turgidiscabies 94.09 (Hi-C-13) was selected in the transposon trap pCZA126, through its insertion into the lambda cI857 repressor. IS1629 is present in multiple copies in some S. scabies strains and is present in all S. acidiscabies and S. turgidiscabies strains examined. A second copy of IS1629 was identified between ORFtnp and nec1 in S. acidiscabies strains. The diversity of IS1629 hybridization profiles was greatest within S. scabies. IS1629 was absent from the 27 nonpathogenic Streptomyces strains tested. The genetic organization and nucleotide sequence of the nec1-IS1629 region was conserved and identical among representatives of S. acidiscabies and S. turgidiscabies. These findings support our current model for the unidirectional transfer of the ORFtnp-nec1-IS1629 locus from IS1629-containing S. scabies (type II) to S. acidiscabies and S. turgidiscabies. (+info)
Natural occurrence of the C series of fumonisins in moldy corn.
We analyzed 44 moldy corn samples for the B and C series of fumonisins by high-performance liquid chromatography. Of the 44 samples, 32 (73%) were contaminated with both the B and C series of fumonisins and 6 were contaminated with only the B series of fumonisins. The incidence of fumonisin C1 in moldy corn was 71%; the incidence was 11% for fumonisin C3 and 43% for fumonisin C4. Their mean levels ranged from 500 to 1,900 ng/g. This is the first report on the natural occurrence of the C series of fumonisins and fumonisin B4 in moldy corn. (+info)
Temporal and multiple quantitative trait loci analyses of resistance to bacterial wilt in tomato permit the resolution of linked loci.
Ralstonia solanacearum is a soil-borne bacterium that causes the serious disease known as bacterial wilt in many plant species. In tomato, several QTL controlling resistance have been found, but in different studies, markers spanning a large region of chromosome 6 showed strong association with the resistance. By using two different approaches to analyze the data from a field test F3 population, we show that at least two separate loci approximately 30 cM apart on this chromosome are most likely involved in the resistance. First, a temporal analysis of the progression of symptoms reveals a distal locus early in the development of the disease. As the disease progresses, the maximum LOD peak observed shifts toward the proximal end of the chromosome, obscuring the distal locus. Second, although classical interval mapping could only detect the presence of one locus, a statistical "two-QTL model" test, specifically adapted for the resolution of linked QTL, strongly supported the hypothesis for the presence of two loci. These results are discussed in the context of current molecular knowledge about disease resistance genes on chromosome 6 and observations made by tomato breeders during the production of bacterial wilt-resistant varieties. (+info)
Enhanced resistance to bacterial diseases of transgenic tobacco plants overexpressing sarcotoxin IA, a bactericidal peptide of insect.
Sarcotoxin IA is a bactericidal peptide of 39 amino acids found in the common flesh fly, Sarcophaga peregrina. Many agronomically important bacteria in Japan are killed by this peptide at sub-micro molar levels, and the growth of tobacco and rice suspension cultured cells is not inhibited with less than 25 microM. Transgenic tobacco plants which overexpress the peptide, i.e. over 250 pmol per gram of fresh leaf, under the control of a high expression constitutive promoter showed enhanced resistance to the pathogens for wild fire disease (Pseudomonas syringae pv. tabaci) and bacterial soft rot disease (Erwinia carotovora subsp. carotovora). (+info)
Expression of alfalfa mosaic virus coat protein in tobacco mosaic virus (TMV) deficient in the production of its native coat protein supports long-distance movement of a chimeric TMV.
Alfalfa mosaic virus (AlMV) coat protein is involved in systemic infection of host plants, and a specific mutation in this gene prevents the virus from moving into the upper uninoculated leaves. The coat protein also is required for different viral functions during early and late infection. To study the role of the coat protein in long-distance movement of AlMV independent of other vital functions during virus infection, we cloned the gene encoding the coat protein of AlMV into a tobacco mosaic virus (TMV)-based vector Av. This vector is deficient in long-distance movement and is limited to locally inoculated leaves because of the lack of native TMV coat protein. Expression of AlMV coat protein, directed by the subgenomic promoter of TMV coat protein in Av, supported systemic infection with the chimeric virus in Nicotiana benthamiana, Nicotiana tabacum MD609, and Spinacia oleracea. The host range of TMV was extended to include spinach as a permissive host. Here we report the alteration of a host range by incorporating genetic determinants from another virus. (+info)
Mechanisms of arthropod transmission of plant and animal viruses.
A majority of the plant-infecting viruses and many of the animal-infecting viruses are dependent upon arthropod vectors for transmission between hosts and/or as alternative hosts. The viruses have evolved specific associations with their vectors, and we are beginning to understand the underlying mechanisms that regulate the virus transmission process. A majority of plant viruses are carried on the cuticle lining of a vector's mouthparts or foregut. This initially appeared to be simple mechanical contamination, but it is now known to be a biologically complex interaction between specific virus proteins and as yet unidentified vector cuticle-associated compounds. Numerous other plant viruses and the majority of animal viruses are carried within the body of the vector. These viruses have evolved specific mechanisms to enable them to be transported through multiple tissues and to evade vector defenses. In response, vector species have evolved so that not all individuals within a species are susceptible to virus infection or can serve as a competent vector. Not only are the virus components of the transmission process being identified, but also the genetic and physiological components of the vectors which determine their ability to be used successfully by the virus are being elucidated. The mechanisms of arthropod-virus associations are many and complex, but common themes are beginning to emerge which may allow the development of novel strategies to ultimately control epidemics caused by arthropod-borne viruses. (+info)
Divinyl ether fatty acid synthesis in late blight-diseased potato leaves.
We conducted a study of the patterns and dynamics of oxidized fatty acid derivatives (oxylipins) in potato leaves infected with the late-blight pathogen Phytophthora infestans. Two 18-carbon divinyl ether fatty acids, colneleic acid and colnelenic acid, accumulated during disease development. To date, there are no reports that such compounds have been detected in higher plants. The divinyl ether fatty acids accumulate more rapidly in potato cultivar Matilda (a cultivar with increased resistance to late blight) than in cultivar Bintje, a susceptible cultivar. Colnelenic acid reached levels of up to approximately 24 nmol (7 microgram) per g fresh weight of tissue in infected leaves. By contrast, levels of members of the jasmonic acid family did not change significantly during pathogenesis. The divinyl ethers also accumulated during the incompatible interaction of tobacco with tobacco mosaic virus. Colneleic and colnelenic acids were found to be inhibitory to P. infestans, suggesting a function in plant defense for divinyl ethers, which are unstable compounds rarely encountered in biological systems. (+info)