Lyso-phosphatidylcholine is a signal in the arbuscular mycorrhizal symbiosis

The arbuscular mycorrhizal (AM) symbiosis represents the most widely distributed mutualistic root symbiosis. We report that root extracts of mycorrhizal plants contain a lipophilic signal capable of inducing the phosphate transporter genes StPT3 and StPT4 of potato (Solanum tuberosum L.), genes that are specifically induced in roots colonized by AM fungi. The same signal caused rapid extracellular alkalinization in suspension-cultured tomato (Solanum lycopersicum L.) cells and induction of the mycorrhiza-specific phosphate transporter gene LePT4 in these cells. The active principle was characterized as the lysolipid lyso-phosphatidylcholine (LPC) via a combination of gene expression studies, alkalinization assays in cell cultures, and chromatographic and mass spectrometric analyses. Our results highlight the importance of lysophospholipids as signals in plants and in particular in the AM symbiosis

Transcriptional profiling of Medicago truncatula roots after infection with Aphanomyces euteiches (oomycota) identifies novel genes upregulated during this pathogenic interaction

Nyamsuren O, Colditz F, Rosendahl S, et al. Transcriptional profiling of Medicago truncatula roots after infection with Aphanomyces euteiches (oomycota) identifies novel genes upregulated during this pathogenic interaction. PHYSIOLOGICAL AND MOLECULAR PLANT PATHOLOGY. 2003;63(1):17-26.Common root rot of pea caused by Aphanomyces euteiches has been the major yield-reducing factor for pea production during the last decades. In this study, a systematic sequencing of expressed sequence tags (ESTs) was chosen to obtain a first global picture of the assembly of genes involved in pathogenesis. For this purpose, a pathosystem between the model legume Medicago truncatula and A. euteiches was established. Typical symptoms of this disease such as root discoloration and a reduction of root mass were observed in the model legume. Significant transcriptional changes in the host plant occurred already 6 days after inoculation. To identify a large number of plant ESTs, which are induced at this time point, a cDNA-library was established by Suppression Subtractive Hybridization. Five hundred and sixty ESTs have been generated of this library. On the one hand, EST-annotations showed homologies to a number of classical pathogenesis-related (PR) and defense genes. A notable number of the ESTs, however, were derived from novel genes not matching entries of the large-scale M. truncatula sequence collection. Hybridization experiments showed that also within these new ESTs, 21% are induced after pathogen infection. Hence. the here presented transcriptomic approach demonstrates that classical pathogenesis mechanisms as well as new specific gene regulations are involved in root rot disease development caused by A. euteiches. (C) 2003 Elsevier Ltd. All rights reserved

Identification of mycorrhiza-regulated genes with arbuscule development-related expression profile

Grunwald U, Nyamsuren O, Tarnasloukht M, et al. Identification of mycorrhiza-regulated genes with arbuscule development-related expression profile. PLANT MOLECULAR BIOLOGY. 2004;55(4):553-566.Suppressive subtractive hybridisation was applied to the analysis of late stage arbuscular mycorrhizal development in pea. 96 cDNA clones were amplified and 8 1, which carried fragments more than 200 nt in size, were sequence analysed. Among 67 unique fragments, 10 showed no homology and 10 were similar to sequences with unknown function. RNA accumulation of the corresponding 67 genes was analysed by hybridisation of macro-arrays. The cDNAs used as probes were derived from roots of wild type and late mutant pea genotypes, inoculated or not with the AM fungus Glomus mosseae. After calibration, a more than 2.5-fold mycorrhiza-induced RNA accumulation was detected in two independent experiments in the wild type for 25 genes, 22 of which seemed to be induced specifically during late stage AM development. Differential expression for 7 genes was confirmed by RT-PCR using RNA from mycorrhiza and from controls of a different pea cultivar. In order to confirm arbuscule-related expression, the Medicago truncatula EST data base was screened for homologous sequences with putative mycorrhiza-related expression and among a number of sequences with significant similarities, a family of trypsin inhibitor genes could be identified. Mycorrhiza-induced RNA accumulation was verified for five members by real-time PCR and arbuscule-related activation of the promoter could be shown in transgenic roots for one of the genes, MtTi1