The basidiomycete Ustilago maydis is the causal agent of corn smut disease and induces tumor formation during biotrophic growth in its host maize (Zea mays). We have conducted a combined metabolome and transcriptome survey of infected leaves between 1 d post infection (dpi) and 8 dpi, representing infected leaf primordia and fully developed tumors, respectively. At 4 and 8 dpi, we observed a substantial increase in contents of the nitrogen-rich amino acids glutamine and asparagine, while the activities of enzymes involved in primary nitrogen assimilation and the content of ammonia and nitrate were reduced by 50% in tumors compared with mock controls. Employing stable isotope labeling, we could demonstrate that U. maydis-induced tumors show a reduced assimilation of soil-derived 15NO3™ and represent strong sinks for nitrogen. Specific labeling of the free amino acid pool of systemic source leaves with [15N]urea revealed an increased import of organic nitrogen from systemic leaves to tumor tissue, indicating that organic nitrogen provision supports the formation of U. maydis-induced tumors. In turn, amino acid export from systemic source leaves was doubled in infected plants. The analysis of the phloem amino acid pool revealed that glutamine and asparagine are not transported to the tumor tissue, although these two amino acids were found to accumulate within the tumor. Photosynthesis was increased and senescence was delayed in systemic source leaves upon tumor development on infected plants, indicating that the elevated sink demand for nitrogen could determine photosynthetic rates in source leaves.

The aim of the present study was to assess possible adverse effects of transgene expression in leaves of field-grown barley relative to the influence of genetic background and the effect of plant interaction with arbuscular mycorrhizal fungi. We conducted transcript profiling, metabolome profiling, and metabolic fingerprinting of wild-type accessions and barley transgenics with seed-specific expression of (1,3-1, 4)-β-glucanase (GluB) in Baronesse (B) as well as of transgenics in Golden Promise (GP) background with ubiquitous expression of codon-optimized Trichoderma harzianum endochitinase (ChGP). We found more than 1,600 differential transcripts between varieties GP and B, with defense genes being strongly overrepresented in B, indicating a divergent response to subclinical pathogen challenge in the field. In contrast, no statistically significant differences between ChGP and GP could be detected based on transcriptome or metabolome analysis, although 22 genes and 4 metabolites were differentially abundant when comparing GluB and B, leading to the distinction of these two genotypes in principle component analysis. The coregulation of most of these genes in GluB and GP, as well as simple sequence repeat-marker analysis, suggests that the distinctive alleles in GluB are inherited from GP. Thus, the effect of the two investigated transgenes on the global transcript profile is substantially lower than the effect of a minor number of alleles that differ as a consequence of crop breeding. Exposing roots to the spores of the mycorrhizal Glomus sp. had little effect on the leaf transcriptome, but central leaf metabolism was consistently altered in all genotypes.food safety | glucanase | chitinase | sustainability B reeding for improved grain weight, higher grain yield, disease resistance, and climatic adaptation by selection of spontaneous mutations shaped the modern barley (Hordeum vulgare L.) crop plant beginning as early as 10,000 years ago. With the technical advance to generate transgenic crops with improved agronomic performance, it has become necessary to assess the substantial equivalence of transgenic crop plants; that is, validate that no undesired side effect of the genetic modification has occurred relative to their parental lines (see ref. 1 for review). The availability of the "omics" techniques opens the possibility to probe substantial equivalence in nontargeted global analyses, providing unbiased results.We have recently developed a 44-K barley microarray based on the assembly of 444,652 barley ESTs into 28,001 contigs and 22,937 singletons, of which 13,265 are represented on the array (2). In contrast, a comprehensive analysis of the metabolome (i.e., all metabolites in a specimen) is not possible because of the immense diversity of primary and secondary plant metabolites (3, 4). Thus, investigating the metabolome requires the prioritization of metabolite subsets as defined by their physicochemical properties or abundance. Although approaches to metabolite profiling are fueled by a multitude of indiv...

Corynebacterium glutamicum, a Gram-positive soil bacterium employed in the industrial production of various amino acids, is able to use a number of different nitrogen sources, such as ammonium, urea or creatinine. This study shows that l-glutamine serves as an excellent nitrogen source for C. glutamicum and allows similar growth rates in glucose minimal medium to those in ammonium. A transcriptome comparison revealed that the nitrogen starvation response was elicited when glutamine served as the sole nitrogen source, meaning that the target genes of the global nitrogen regulator AmtR were derepressed. Subsequent growth experiments with a variety of mutants defective in nitrogen metabolism showed that glutamate synthase is crucial for glutamine utilization, while a putative glutaminase is dispensable under the experimental conditions used. The gltBD operon encoding the glutamate synthase is a member of the AmtR regulon. The observation that the nitrogen starvation response was elicited at high intracellular l-glutamine levels has implications for nitrogen sensing. In contrast with other Gram-positive and Gram-negative bacteria such as Bacillus subtilis, Salmonella enterica serovar Typhimurium and Klebsiella pneumoniae, a drop in glutamine concentration obviously does not serve as a nitrogen starvation signal in C. glutamicum.

Extensive progress has been made in the last years in unraveling molecular mechanisms of plant-pathogen interactions. Although the main research focus lies on defense and counter-defense mechanisms, some plant-pathogen interactions have been characterized on the physiological level. Only a few studies have focused on the nutrient acquisition strategies of phytopathogens. In a previous study, we analyzed how local infection of maize leaves by the tumorinducing fungus Ustilago maydis affects whole plant physiology and were able to show that carbon and nitrogen assimilates are rerouted to the tumor. While the sink strength of infected emerging young leaves increases with tumor development, systemic source leaves exhibit elevated export of assimilates and delayed senescence to compensate for the altered sink-source balance. Here we provide new experimental data on the metabolization of these assimilates in the tumor and propose a model on their utilization in the infected tissue.Biotrophic plant pathogens depend on living host tissue and need to be able to compete with host cells for the acquisition of nutrients.1 It was shown that by inducing tumors on maize (Zea mays) leaves, the biotrophic basidiomycete fungus Ustilago maydis establishes a strong sink organ for carbohydrates 2-4 and amino acids. 5 These assimilates are provided by systemic source leaves, which exhibit increased productivity and increased export rates compared to comparable leaves of non-infected maize plants. To address how assimilates are metabolized in tumors, we conducted maize transcriptomics at different time points post infection and performed additional physiological analyses on developed tumors that were inspired by the transcript profiling approach. In brief, phenylpropanoid-, AA-, cell wall biosynthesis and enzymes of the TCA cycle are transcriptionally induced in tumors, while sucrose biosynthesis is repressed.3 At the same time, tumor metabolism is characterized by reduced photosynthesis and an accumulation of soluble sugars, i.e., hexoses which are generated via cleavage of sucrose by cell wall and vacuolar invertases.2 In addition, a plasmamembrane-associated sucrose synthase (Sus1) 6 is six-fold induced in tumors. Thus, we propose that sucrose imported from systemic leaves into tumor tissue serves the following main functions in host and pathogen metabolism: (1) provision of building blocks for cell wall biosynthesis of the tumor cell, which is channeled by SUS1, (2) generation of hexoses in the tumor-cell vacuole to build up osmotic pressure for tumor cell-expansion (see Fig. 2) and (3) feeding of U. maydis, which will most likely proceed via the high affinity sucrose transporter SRT1 that can outcompete host sucrose transporters based on its low K M for sucrose and will enable the pathogen to retrieve most of the sucrose.