Development of bioinformatic tools to support EST-sequencing, in silico- and microarray-based transcriptome profiling in mycorrhizal symbioses.

The great majority of terrestrial plants enters a beneficial arbuscular mycorrhiza (AM) or ectomycorrhiza (ECM) symbiosis with soil fungi. In the SPP 1084 "MolMyk: Molecular Basics of Mycorrhizal Symbioses", high-throughput EST-sequencing was performed to obtain snapshots of the plant and fungal transcriptome in mycorrhizal roots and in extraradical hyphae. To focus activities, the interactions between Medicago truncatula and Glomus intraradices as well as Populus tremula and Amanita muscaria were selected as models for AM and ECM symbioses, respectively.

Identification and expression regulation of symbiotically activated legume genes.

Legume plants are able to enter two different endosymbioses with soil prokaryotes and soil fungi, leading to nitrogen-fixing root nodules and to arbuscular mycorrhiza (AM), respectively. We applied in silico and microarray-based transcriptome profiling approaches to uncover the transcriptome of developing root nodules and AM roots of the model legume Medicago truncatula. Several hundred genes were found to be activated in different stages of either symbiosis, with almost 100 genes being co-induced during nodulation and in arbuscular mycorrhiza.

Combined transcriptome profiling reveals a novel family of arbuscular mycorrhizal-specific Medicago truncatula lectin genes.

The large majority of plants are capable of undergoing a tight symbiosis with arbuscular mycorrhizal (AM) fungi. During this symbiosis, highly specialized new structures called arbuscules are formed within the host cells, indicating that, during interaction with AM fungi, plants express AM-specific genetic programs. Despite increasing efforts, the number of genes known to be induced in the AM symbiosis is still low.

The promoter of the leghaemoglobin gene VfLb29: functional analysis and identification of modules necessary for its activation in the infected cells of root nodules and in the arbuscule-containing cells of mycorrhizal roots.

In this study the further characterization of the Vicia faba leghaemoglobin promoter pVfLb29 is presented that was previously shown to be specifically active in the infected cells of root nodules and in arbuscule-containing cells of mycorrhizal roots. Using promoter studies in transgenic hairy roots of the Pisum sativum mutant RisNod24, disabled in the formation of functional arbuscules, VfLb29 promoter activity is assigned to later stages of arbuscule development. In order to narrow down the regions containing cis-acting elements of pVfLb29, the activity of five VfLb29 promoter deletions (-797/-31 to -175/-31 in relation to the start codon) fused to the gusAint coding region were tested in transgenic V.

Transcriptome profiling in root nodules and arbuscular mycorrhiza identifies a collection of novel genes induced during Medicago truncatula root endosymbioses.

Transcriptome profiling based on cDNA array hybridizations and in silico screening was used to identify Medicago truncatula genes induced in both root nodules and arbuscular mycorrhiza (AM). By array hybridizations, we detected several hundred genes that were upregulated in the root nodule and the AM symbiosis, respectively, with a total of 75 genes being induced during both interactions. The second approach based on in silico data mining yielded several hundred additional candidate genes with a predicted symbiosis-enhanced expression.

The promoter of the Vicia faba L. leghemoglobin gene VfLb29 is specifically activated in the infected cells of root nodules and in the arbuscule-containing cells of mycorrhizal roots from different legume and nonlegume plants.

The VfLb29 leghemoglobin gene promoter was polymerase chain reaction-amplified from a Vicia faba genomic library and was fused to the gusAint coding region. Expression of the chimeric gene was analyzed in transgenic hairy roots of the legumes V. faba, V.

The Medicago truncatula sucrose synthase gene MtSucS1 is activated both in the infected region of root nodules and in the cortex of roots colonized by arbuscular mycorrhizal fungi.

The MtSucS1 gene encodes a sucrose synthase (EC 2.4.1.

Transcriptional changes in response to arbuscular mycorrhiza development in the model plant Medicago truncatula.

Significant changes in root morphology and physiology during arbuscular mycorrhiza (AM) development are likely to be controlled by specific gene expression pattern in the host plant. Until now, little was known about transcriptional changes which occur AM-exclusively; that is, they do not occur during other root-microbe associations, nor are they induced by improved phosphate nutrition. In order to identify such AM-exclusive gene inductions of Medicago truncatula, we used a pool of different RNA samples as subtractor population in a suppressive subtractive hybridization (SSH) experiment.