Trifluralin herbicide-induced resistance of melon to fusarium wilt involves expression of stress- and defence-related genes

To identify genes involved in trifluralin herbicide-induced resistance of melon to Fusarium oxysporum f. sp. melonis , suppression subtractive hybridization (SSH) and cDNA-amplified fragment-length polymorphism (cDNA-AFLP) were used. A total of 123 clones—60 of which have never been isolated from melon—were isolated, sequenced and annotated. A significant proportion (35%) of the total 123 clones exhibited similarity to genes that have been formerly described as stress- or defence-related. Thirty-two selected clones were subjected to a detailed expression analysis, one-third of which were found to be up-regulated in response to trifluralin treatment and/or fusarium inoculation. The putative roles of seven of these clones in stress are discussed. Furthermore, the expression of four stress-related and up-regulated genes was enhanced when the plants were subjected to salinity stress, suggesting that trifluralin induces a general stress response which protects the plant against fusarium wilt.     

Nuclear import and export of plant virus proteins and genomes

Nuclear import and export are crucial processes for any eukaryotic cell, as they govern substrate exchange between the nucleus and the cytoplasm. Proteins involved in the nuclear transport network are generally conserved among eukaryotes, from yeast and fungi to animals and plants. Various pathogens, including some plant viruses, need to enter the host nucleus to gain access to its replication machinery or to integrate their DNA into the host genome; the newly replicated viral genomes then need to exit the nucleus to spread between host cells. To gain the ability to enter and exit the nucleus, these pathogens encode proteins that recognize cellular nuclear transport receptors and utilize the host's nuclear import and export pathways. Here, we review and discuss our current knowledge about the molecular mechanisms by which plant viruses find their way into and out of the host cell nucleus.     

Mitochondrial Interaction with Helminthosporium maydis Race T Toxin: Blocking by Dicyclohexylcarbodiimide

Treatment of mitochondria isolated from Texas male sterile cytoplasmcorn (T mitochondria) with high concentrations of dicyclohexylcarbodiimide(DCCD) (140 nmol DCCD mg^–1 mitochondrial protein) completelyand immediately inhibited T mitochondrial swelling by Helminthosporiummaydis Race T toxin (HmT toxin). In order to obtain a specificinteraction between DCCD and the ATPase complex T mitochondriawere incubated with lower DCCD concentrations (1–5 nmolDCCD mg^–1 mitochondrial protein) for up to 8 h at 4 °C.After 8 h incubation in the presence of 3.75 nmol DCCD mg^–1mitochondrial protein, toxin-induced swelling was decreasedby 69%. Specificity of DCCD action upon the ATPase complex wasconfirmed by (1) SDS gel electrophoresis and fluorographic analysesof proteins from [¹⁴C]-DCCD-treated T mitochondria and immunoprecipitatesand (2) physiological experiments showing that DCCD exertednone of its other documented effects. These data suggest thatHmT toxin interacts with the ATPase complex of T mitochondriaeither at or near the DCCD-binding protein within the membranesector of the complex. Key words: Zea mays L., Helminthosporium maydis, Mitochondria     

Phylogeny of Acomys spinosissimus (Rodentia, Muridae) from north Malawi and Tanzania: evidence from morphological and molecular analysis

New specimens of Acomys spinosissimus from northern Malawi and southern Tanzania were subjected to morphological, molecular (cytochrome b mitochondrial gene) and cytogenetical analysis in order to establish the phylogenetic position of these populations among A. spinosissimus, as well as their relationships with other species (A. subspinosus and A. wilsoni). The monophyly of the spinosissimus clade is supported by morphological and molecular phylogenies. Cytogenetics and morphology, but not the cytochrome b phylogeny show the possible existence of two sibling species within spinosissimus. Incongruences are noted between molecular and morphological trees, especially concerning the position of the Transvaal specimens. Two different biogeographic scenarios for the origin and dispersal of A. spinosissimus are discussed in the light of available palaeontological data.     

The roles of plant phenolics in defence and communication during Agrobacterium and Rhizobium infection

Phenolics are aromatic benzene ring compounds with one or more hydroxyl groups produced by plants mainly for protection against stress. The functions of phenolic compounds in plant physiology and interactions with biotic and abiotic environments are difficult to overestimate. Phenolics play important roles in plant development, particularly in lignin and pigment biosynthesis. They also provide structural integrity and scaffolding support to plants. Importantly, phenolic phytoalexins, secreted by wounded or otherwise perturbed plants, repel or kill many microorganisms, and some pathogens can counteract or nullify these defences or even subvert them to their own advantage. In this review, we discuss the roles of phenolics in the interactions of plants with Agrobacterium and Rhizobium.     

Pectolytic Activity by the Haustorium of the Parasitic PlantOrobancheL. (Orobanchaceae) in Host Roots

The possible involvement of enzymes in the penetration of intrusivecells of the parasitic angiospermOrobancheinto host root tissueswas studied using cytochemical and immunocytochemical methods.Pectin methyl esterase (PME) was detected, with specific antibodies,in the cytoplasm and cell walls ofOrobancheintrusive cells andin adjacent host apoplast. Depletion and chemical changes ofpectins in host cell walls were shown by histochemical stainingwith PATAg, which detects carbohydrates that are sensitive toperiodic acid, especially pectins, and with the monoclonal antibodiesJIM 5 and JIM 7 that label pectins with low and high rates ofesterification, respectively. Galacturonic sequences with lowrates of esterification were more abundant in host cell wallsadjacent to the parasite, which is consistent with pectin de-methylationby PME release from the parasite. Pectins were absent in middlelamellae and in host cell walls neighbouring mature intrusivecells of the parasite, consistent with further degradation ofpectins by other enzymes. These results provide the first directevidence for the presence and activity of a pectolytic enzymein the infection zone of the haustorium of a parasitic angiosperminsitu.Copyright 1998 Annals of Botany Company Broomrape;Orobanche; parasitic weed; haustorium; pectin methyl esterase; pectin; cell wall.     

The Angiospermous Root ParasiteOrobancheL. (Orobanchaceae) Induces Expression of a Pathogenesis Related (PR) Gene in Susceptible Tobacco Roots

Parasitic plants develop a haustorium that intrudes host tissues.In roots of transgenic PRb-1b-GUS tobacco the expression ofthe chimeric gene was prominent nearOrobancheinfection. Theexpression of the pathogenesis related (PR) protein gene inOrobanche-infectedroots indicates thatOrobanchereleases appropriate elicitors,and that the susceptible plant does senseOrobancheinvasion.TheOrobanche-responsive promoter may be a useful tool in engineeringresistances to this parasitic weed.Copyright 1998 Annals ofBotany Company Haustorium,Nicotiana tabacum, Orobanche aegyptiaca, parasitic plants, PR proteins, tobacco.