Adaptation of maize source leaf metabolism to stress related disturbances in carbon, nitrogen and phosphorus balance

Schlueter U, Colmsee C, Scholz U, et al. Adaptation of maize source leaf metabolism to stress related disturbances in carbon, nitrogen and phosphorus balance. BMC Genomics. 2013;14(1): 442.Background: Abiotic stress causes disturbances in the cellular homeostasis. Re-adjustment of balance in carbon, nitrogen and phosphorus metabolism therefore plays a central role in stress adaptation. However, it is currently unknown which parts of the primary cell metabolism follow common patterns under different stress conditions and which represent specific responses. Results: To address these questions, changes in transcriptome, metabolome and ionome were analyzed in maize source leaves from plants suffering low temperature, low nitrogen (N) and low phosphorus (P) stress. The selection of maize as study object provided data directly from an important crop species and the so far underexplored C-4 metabolism. Growth retardation was comparable under all tested stress conditions. The only primary metabolic pathway responding similar to all stresses was nitrate assimilation, which was down-regulated. The largest group of commonly regulated transcripts followed the expression pattern: down under low temperature and low N, but up under low P. Several members of this transcript cluster could be connected to P metabolism and correlated negatively to different phosphate concentration in the leaf tissue. Accumulation of starch under low temperature and low N stress, but decrease in starch levels under low P conditions indicated that only low P treated leaves suffered carbon starvation. Conclusions: Maize employs very different strategies to manage N and P metabolism under stress. While nitrate assimilation was regulated depending on demand by growth processes, phosphate concentrations changed depending on availability, thus building up reserves under excess conditions. Carbon and energy metabolism of the C-4 maize leaves were particularly sensitive to P starvation

Charakterisierung der Nichtwirt-Interaktion zwischen Gerste und Pilzen der Gattung Magnaporthe

Nonhost-resistance (NHR) is the resistance shown by a plant species towards all isolates of a pathogen species. This durable type of resistance protects plants against the majority of potential pathogens. In this thesis the nonhost-interaction between barley and isolates of the fungal genus Magnaporthe was analysed and compared to the host-interaction. Magnaporthe was isolated from different host plants, and the different isolates were examined for their biological relationship to one another and for their capacity to infect barley. It was shown that all isolates which were able to cause disease symptoms on barley (host-interaction) belong to the species M. oryzae. In contrast, M. grisea isolates (host: Digitaria) and isolates of a putative novel species which is associated with the host Pennisetum could not reproduce on barley (nonhost-interaction). Comparative cytological analyses showed that formation of papillae (penetration resistance) and hypersensitive epidermal cell death (postpenetration resistance) were predominant nonhost-defense mechanisms. These reactions were apparent by 24 h p.i. at higher frequencies in the nonhost-interaction than in the host-interaction. It was possible to significantly reduce the penetration resistance of barley by treatments with AIP (an inhibitor of phenylalanine ammonia lyase) and cytochalasin E (an inhibitor of actin-polymerisation). Similarly, penetration resistance was reduced in the barley mutant mlo-5 ror1-2 rar1-2. However, growth of the nonhost-pathogen was arrested in epidermal cells in all cases and the pathogen was never able to generate secondary hyphae. These results underpin the effectiveness of epidermal defence in this nonhost-interaction. Complementary-DNA macroarray-analysis of inoculated barley-epidermis showed a very early (6 h p.i.) and pronounced change in the pattern of gene-expression in the nonhost-interaction as compared to the host-interaction. Particularly, the expression of genes involved in lipid metabolism was induced significantly after inoculation with the nonhost-pathogen. For functional analysis of these candidate genes virus-induced gene silencing technology (VIGS) was established for the barley/Magnaporthe-interaction. Results presented here indicate similarities between the NHR and basal resistance of barley towards fungi of the genus Magnaporthe. In general, barley responds to pathogen attack with a similar spectrum of defence mechanisms in nonhost- or host-interactions, but activation of these defences occurs earlier and more efficiently in the nonhost- than in the host-interaction. This phenomenon might depend on an early recognition of nonhost-specific effector molecules by barley. In contrast, the suppression of plant defence by effectors of host-pathogens might be responsible for the delayed defence in the host-interaction. Remarkably, a comparative transcriptome-analysis of three different nonhost-interactions of barley (barley/Magnaporthe, barley/powdery mildew, barley/rust) revealed no genes which were regulated in a similar manner in all interactions. These results point to a pathogen-specific reprogramming of the plant metabolism in nonhost-interactions. During further investigations the significance of the Rom1 gene for the interaction of barley with different species of the genus Magnaporthe was analysed. The mutation in Rom1 restores the resistance of susceptible Mla12 rar1-2 Rom1 (rar1-2) barley against the powdery mildew fungus Bgh. Remarkably, after infection with M. oryzae, plants of the genotype Mla12 rar1-2 rom1 (rom1) showed more but smaller disease symptoms than wildtype and rar1-2-plants. Thus, Rom1 and Rar1 appear to act antagonistically in epidermal and mesophyll defence scenarios. Moreover, rom1-plants showed a higher accumulation of PR1b-specific transcripts after inoculation with the Magnaporthe nonhost-pathogen in comparison to wildtype and rar1-2-plants. This may argue for an augmented responsiveness of rom1-plants. Furthermore, the influence of the gene Rac1, whose overexpression is known to cause hypersusceptibility of barley to Bgh, was investigated in the barley/M. oryzae interaction. In macro- and microscopical analyses a correlation between increased resistance of Rac1-overexpression lines against M. oryzae and augmented penetration resistance was observed. These results point to an influence of Rom1 and Rac1 on basal resistance and, in the case of Rom1, on the NHR of barley against different pathogens

Barley stripe mosaic virus-induced gene silencing (BSMV-IGS) as a tool for functional analysis of barley genes potentially involved in nonhost resistance

Barley is an alternative host for the rice blast fungus Magnaporthe oryzae but is resistant to Magnaporthe species associated with the grass genera Pennisetum and Digitaria. The latter cases are examples for nonhost resistance which confers effective and durable protection to plants against a broad spectrum of pathogens. Comparative transcript profiling of host and nonhost interaction revealed an early and pronounced change in gene expression in epidermal tissue of barley infected with a Magnaporthe nonhost isolate. Interestingly, this set of genes did not overlap considerably with the transcriptional response of barley against nonhost rust or powdery mildew isolates. For a functional testing of candidate genes a combined approach of virus-induced gene silencing (VIGS) and subsequent pathogen challenge was established. As anticipated, VIGS-mediated downregulation of Mlo-transcripts led to higher resistance against Blumeria graminis f.sp. hordei and enhanced susceptibility against M. oryzae

St. John's Daily Star, 1920-08-20

The St. John's Daily Star was published daily except Sunday between 17 April 1915 - 23 July 1921

Barley Rom1 antagonizes Rar1 function in Magnaporthe oryzae-infected leaves by enhancing epidermal and diminishing mesophyll defence

* Barley (Hordeum vulgare) is a host for Blumeria graminis f. sp. hordei (Bgh), which causes powdery mildew, and for the rice blast pathogen Magnaporthe oryzae. It has previously been shown that Rar1, initially identified in a mutational screen as being required for Mla12-specified Bgh-resistance, also controlled pathogenic growth of M. oryzae in barley. Here, we tested whether the rom1 mutation (restoration of Mla12-specified resistance), which restored resistance against Bgh in a susceptible rar1-2 genetic background, also influences the interaction between barley and M. oryzae. * Disease severity after infection with M. oryzae was analysed on rar1-2 mutants and rar1-2 rom1 double mutants. Microscopy and northern analysis were used to gain insight into cellular and molecular events. * On rar1-2 rom1 double mutant plants, the number of M. oryzae disease lesions was increased in comparison to the wild-type and the rar1-2 mutant which correlated with augmented epidermal penetration. However, a decrease in the lesion diameter, apparently conditioned in the mesophyll, was also observed. * These results highlight the impact of Rom1 in basal defence of barley against different pathogens. Importantly, a tissue-specific function for Rom1 with contrasting effects on epidermal and mesophyll defence was demonstrated

OPTIMAS-DW: A comprehensive transcriptomics, metabolomics, ionomics, proteomics and phenomics data resource for maize

<p>Abstract</p> <p>Background</p> <p>Maize is a major crop plant, grown for human and animal nutrition, as well as a renewable resource for bioenergy. When looking at the problems of limited fossil fuels, the growth of the world’s population or the world’s climate change, it is important to find ways to increase the yield and biomass of maize and to study how it reacts to specific abiotic and biotic stress situations. Within the OPTIMAS systems biology project maize plants were grown under a large set of controlled stress conditions, phenotypically characterised and plant material was harvested to analyse the effect of specific environmental conditions or developmental stages. Transcriptomic, metabolomic, ionomic and proteomic parameters were measured from the same plant material allowing the comparison of results across different omics domains. A data warehouse was developed to store experimental data as well as analysis results of the performed experiments.</p> <p>Description</p> <p>The OPTIMAS Data Warehouse (OPTIMAS-DW) is a comprehensive data collection for maize and integrates data from different data domains such as transcriptomics, metabolomics, ionomics, proteomics and phenomics. Within the OPTIMAS project, a 44K oligo chip was designed and annotated to describe the functions of the selected unigenes. Several treatment- and plant growth stage experiments were performed and measured data were filled into data templates and imported into the data warehouse by a Java based import tool. A web interface allows users to browse through all stored experiment data in OPTIMAS-DW including all data domains. Furthermore, the user can filter the data to extract information of particular interest. All data can be exported into different file formats for further data analysis and visualisation. The data analysis integrates data from different data domains and enables the user to find answers to different systems biology questions. Finally, maize specific pathway information is provided.</p> <p>Conclusions</p> <p>With OPTIMAS-DW a data warehouse for maize was established, which is able to handle different data domains, comprises several analysis results that will support researchers within their work and supports systems biological research in particular. The system is available at <url>http://www.optimas-bioenergy.org/optimas_dw</url>.</p