Aspects of the biology of Brassica/Alternaria host/pathogen systems

The main purpose of this study was to further an understanding of host-pathogen interactions and th e role of phytotoxins in the host relationships of Altemaria brassicae(Berk.) Sacc. and Alternariabrassicicola(Schw.) Wilts., using microscopical, biochemical, and statistical approaches. A further aim was to assess the taxonomic positions of A.brassicae and A.brassicicola within the Altemaria along with their attributes and behaviour patterns in relation to other members of the anamorph-genus.OOn the leaf surfaces of host plants A.brassicae and A.brassicicola showed broadly similar patterns of development but with some features which distinguished them. T he larger spores of A.brassicae typically produced two to three germ -tubes whereas A.brassicicola gave rise to only one. A.brassicae generally produced m ore extensive extra-matrical growth with hyphal branching and appressoria in intercalary as well as terminal positions; hyphae of A.brassicicola produced very few branches and usually terminated in appressoria. For both fungi appressoria were formed most frequently near to or over anticlinal walls of epidermal cells. Smaller numbers of appressoria were formed over periclinal walls and, in the case of A.brassicae, over stomata. The extra-matrical development of both species was m ore or less similar on contrasting host leaf surfaces, although A.brassicae showed somewhat reduced germ -tube numbers and stomatal penetrations on leaves with a pronounced waxy bloom. M arked differences in behaviour on different hosts or between hosts and non-hosts were evident only after penetration. In the case of A.brassicae unsuccessful penetrations were associated with only localised deposition of callose in the cell wall of the challenged cell, while with A.brassicicolaun successful penetration events were associated with cell wall responses which occurred in whole single cells.In comparing A.brassicae and A. brassicicola with other Altemaria species varying in their host range and degree of parasitism, all exhibited essentially similar patterns of extra-matrical behaviour on leaves, culminating in the formation of appressoria. Distinctive host relationships were evident only in the post-penetration phase.From successful penetrations A.brassicae produced a short sub-cuticular phase whereas A.brassicicola appeared to penetrate to intracellular position in the epidermis. Subsequent colonisation involved intercellular hyphal growth and extensive callose formation in host cell walls in response to both species.Biochemical studies on different Altemaria species indicated that each produced a diverse range of metabolites which may exhibit fungitoxic and phytotoxic activity. In the present study cytotoxicity of the extracts was low. T he studies failed to identify host-specific phytotoxicity, as only crude extracts were used, but the critical role of a host specific toxin, or resistance suppressor, is postulated in the initial establishment of infection.In considering genetical variation within A.brassicae and A.brassicicola, there is little evidence of marked physiological specialisation in either species. However, in testing a small number of isolates against a dicarboximide fungicide, A.brassicae showed slight and A.brassicicola showed marked intraspecific variation in fungicide insensitivity. In testing for sensitivity to fungicides the isolates of A.brassicae used w ere found to exhibit distinctive colony growth characteristics.Multivariate statistical techniques were applied to morphological, biochemical, and pathogenic characters to examine phylogenic relationships between selected species of Altemaria.Studies of the taxonomic relationships of the Altemariaspecies are constrained by the absence of teleomorphs, but certain genera within the Pleosporaceae are suggested to accommodate this group of toxigenic, leaf spotting, facultative parasites / saprophytes

Sclerotinia sclerotiorum necrosis-inducing effectors

Stem rot disease in canola caused by Sclerotinia sclerotiorum leads to lodging and severe yield losses in Canada. Sclerotinia sclerotiorum is equipped with small, secreted proteins (effectors) to induce plant cell death to facilitate nutrient uptake. Characterizing cell death/necrosis-inducing effectors might enable devising strategies to identify disease tolerant germplasm that is impervious to select necrosis-inducing effectors. In this study, RNA-Seq analysis was performed with a focus on the events occurring through the early (1 hour) to the middle (48 hours) stages of infection to reveal the gene expression patterns during the course of S. sclerotiorum infection on B. napus. The differentially expressed genes including those encoding hydrolytic enzymes, secreted effectors, enzymes involved in the synthesis of secondary metabolites or their detoxification, signaling, development, as well as oxalic acid and reactive oxygen species production. This investigation provides a broad overview of the sequential expression of virulence/pathogenicity-associated genes during infection of B. napus. To identify candidate necrosis-inducing effectors, the genome of S. sclerotiorum was searched for genes encoding small, secreted, cysteine-rich proteins. These effectors were tested for their ability to induce necrosis in Nicotiana benthamiana via Agrobacterium tumefaciens-mediated transient expression and for their host cellular localization. Six novel necrosis-inducing effectors were discovered, of which all but one required a signal peptide and secretion to the extracellular space for necrotic activity. These five effectors were localized to the endoplasmic reticulum and nucleus, while one that did not require signal peptide for necrotizing activity was localized in cytoplasm and nucleus. Virus-induced gene silencing (VIGS) experiments were conducted to reveal the participation of plant receptor-like kinases (RLK) in the induction of cell death. VIGS revealed that these five effectors required the RLKs, BAK1 and SOBIR1, for the induction of necrosis. These results illustrated the importance of necrosis-inducing effectors for S. sclerotiorum virulence and the potential role of host extra-cellular receptor(s) in the perception of S. sclerotiorum effectors. Substitution of cysteine residues with alanine and examination of truncated peptides for one of these effectors suggested that the native protein is necessary for necrotizing activity. These effectors could be applied for effector-assisted breeding of resistance to stem rot disease in canola

Program and abstracts from the 24th Fungal Genetics Conference

Abstracts of the plenary and poster sessions from the 24th Fungal Genetics Conference, March 20-25, 2007, Pacific Grove, CA

Toward Direct Biosynthesis of Drop-in Ready Biofuels in Plants: Rapid Screening and Functional Genomic Characterization of Plant-derived Advanced Biofuels and Implications for Coproduction in Lignocellulosic Feedstocks

Advanced biofuels that are “drop-in” ready, completely fungible with petroleum fuels, and require minimal infrastructure to process a finished fuel could provide transportation fuels in rural or developing areas. Five oils extracted from Pittosporum resiniferum, Copaifera reticulata, and surrogate oils for Cymbopogon flexuosus, C. martinii, and Dictamnus albus in B20 blends were sent for ASTM International biodiesel testing and run in homogenous charge combustion ignition engines to determine combustion properties and emissions. All oils tested lowered cloud point. Oils derived from Copaifera reticulata also lowered indicated specific fuel consumption and had emissions similar to the ultra-low sulfur diesel control. Characterization of the biosynthetic pathways responsible for the sesquiterpene-rich Copaifera-derived oils could lead to production of these oils in biofuel feedstocks. The Copaifera officinalis transcriptome sequencing, assembly, and annotation identified eight terpene synthase genes in C. officinalis and C. langsdorffii that produced mono- and sesquiterpene products in functional assays. The terpene synthases characterized produced the major fraction of sesquiterpenes identified in C. officinalis leaf, stem, and root tissues as well as the oils tested previously. This initial characterization will support future investigation of sesquiterpene biosynthesis in the Copaifera genus to understand how liters of sesquiterpene oils are produced for biotechnology applications and the mechanism responsible for the geographical biochemical variation seen in sesquiterpene-producing New World species compared to diterpene-producing African species. Lastly, Cymbopogon flexuosus and C. martinii biomass production in small field trials, as well as oil and ethanol yield from biomass were investigated to determine the feasibility of producing the advanced biofuels in lignocellulosic feedstocks. C. flexuosus and C. martinii ethanol yields from biomass were lower than Panicum virgatum, but had an average oil yield of 85.7 kg ha-1 [ha^-1] and 67.0 kg ha-1 [ha^-1], respectively. Combined ethanol and oil value for C. flexuosus and C. martinii were higher than P. virgatum ethanol value. This suggests that the oils from C. flexuosus and C. martinii are more suitable as high-value fermentation coproducts rather than as low-value advanced biofuels. Increasing yield of oil or alternative production schemes could lead to economically feasible advanced biofuel production

Recent advances in allelopathy (Vol. 1)

The discovery of new allelochemicals from plants and microbes has attracted our attention in the last 20 years due to their ecological implications as biocommunicators in nature and to their potential use as a source of new structural types of agrochemicals. Recent Advances in Aiieiopathyis a new triennial scientific series which has been born with the aim of collecting whatever can be considered relevant in the field of Allelopathy research within a period of three years, considering every aspect of this multidisciplinary science. This first volume A Science for the Future presents a selected number of chapters in which internationally renowned experts discuss how a better understanding of allelochemical phenomena can lead to natural applications. Ifwe know the way thatplants madepossible theirinter- andintraspecific relationship within a specific ecosystem, we can mimic certain processes and think in applications as natural herbicides, antibiotics, fungicides, natural insecticides, etc. This book is divided into four sections: I) Methodology and Techniques in Allelopathic Studies. II) Chemistry, Physiology and MechanismofAllelopathic Processes. Ill) Allelopathic Interactions in Nature. IV) Allelopathy in Weed and Plant Disease Control. It presents an overview of the different fields involved in Allelopathy in an integrated way. We hope that this book will help, both those people that read for the first time about Allelopathy and those that have been working for a hard long time in the research and development of Allelopathy, get enthusiastic about Allelopathy