Transcriptional snapshots provide insights into the molecular basis of arbuscular mycorrhiza in the model legume Medicago truncatula

Hohnjec N, Henckel K, Bekel T, et al. Transcriptional snapshots provide insights into the molecular basis of arbuscular mycorrhiza in the model legume Medicago truncatula. FUNCTIONAL PLANT BIOLOGY. 2006;33(8):737-748.The arbuscular mycorrhizal (AM) association between terrestrial plants and soil fungi of the phylum Glomeromycota is the most widespread beneficial plant-microbe interaction on earth. In the course of the symbiosis, fungal hyphae colonise plant roots and supply limiting nutrients, in particular phosphorus, in exchange for carbon compounds. Owing to the obligate biotrophy of mycorrhizal fungi and the lack of genetic systems to study them, targeted molecular studies on AM symbioses proved to be difficult. With the emergence of plant genomics and the selection of suitable models, an application of untargeted expression pro. ling experiments became possible. In the model legume Medicago truncatula, high-throughput expressed sequence tag (EST)-sequencing in conjunction with in silico and experimental transcriptome pro. ling provided transcriptional snapshots that together defined the global genetic program activated during AM. Owing to an asynchronous development of the symbiosis, several hundred genes found to be activated during the symbiosis cannot be easily correlated with symbiotic structures, but the expression of selected genes has been extended to the cellular level to correlate gene expression with specific stages of AM development. These approaches identified marker genes for the AM symbiosis and provided the first insights into the molecular basis of gene expression regulation during AM

THE NODULE-SPECIFIC VFENOD-GRP3 GENE ENCODING A GLYCINE-RICH EARLY NODULIN IS LOCATED ON CHROMOSOME-I OF VICIA-FABA L AND IS PREDOMINANTLY EXPRESSED IN THE INTERZONE II-III OF ROOT-NODULES

Küster H, SCHRODER G, FRUHLING M, et al. THE NODULE-SPECIFIC VFENOD-GRP3 GENE ENCODING A GLYCINE-RICH EARLY NODULIN IS LOCATED ON CHROMOSOME-I OF VICIA-FABA L AND IS PREDOMINANTLY EXPRESSED IN THE INTERZONE II-III OF ROOT-NODULES. PLANT MOLECULAR BIOLOGY. 1995;28(3):405-421.A nodule-specific cDNA was isolated from a Vicia faba L. nodule cDNA library. Since time course experiments revealed an early expression of this transcript in the nodule, this cDNA coded for an early nodulin and was designated VfENOD-GRP3. Based on tissue print hybridizations, we found a predominant expression of VfENOD-GRP3 transcripts in the interzone II-III region of broad bean root nodules. The encoded early nodulin ENOD-GRP3 was characterized by an N-terminal signal peptide and a C-terminal domain displaying a glycine content of 31%. Sequence analysis of a genomic VfENOD-GRP3 clone revealed that the signal peptide and the glycine-rich domain were specified by two separate exons. Primer extension experiments identified two adjacent transcription start sites for VfENOD-GRP3 transcripts. The common nodulin sequences 'AAAGAT' and 'CTCTT' were present five and three times on both DNA strands of the putative VfENOD-GRP3 promoter, respectively. Additionally, three sequence motifs resembling organ-specific elements of the soybean lbc3 gene promoter and a sequence similar to the binding site 1 for the nodule trans-acting factor Nat2 were identified. From Southern blot data and from sequence analysis of genomic PCR fragments, the presence of a VfENOD-GRP3 gene family was inferred. By PCR experiments using sequence-specific primers and DNA of microisolated chromosomes as a template, this family was located on the long arm of chromosome I