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Publications - Cell and Metabolic Biology

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Publications

Grunwald, U.; Guo, W.; Fischer, K.; Isayenkov, S.; Ludwig-Müller, J.; Hause, B.; Yan, X.; Küster, H.; Franken, P.; Overlapping expression patterns and differential transcript levels of phosphate transporter genes in arbuscular mycorrhizal, Pi-fertilised and phytohormone-treated Medicago truncatula roots Planta 229, 1023-1034, (2009) DOI: 10.1007/s00425-008-0877-z

A microarray carrying 5,648 probes of Medicago truncatula root-expressed genes was screened in order to identify those that are specifically regulated by the arbuscular mycorrhizal (AM) fungus Gigaspora rosea, by Pi fertilisation or by the phytohormones abscisic acid and jasmonic acid. Amongst the identified genes, 21% showed a common induction and 31% a common repression between roots fertilised with Pi or inoculated with the AM fungus G. rosea, while there was no obvious overlap in the expression patterns between mycorrhizal and phytohormone-treated roots. Expression patterns were further studied by comparing the results with published data obtained from roots colonised by the AM fungi Glomus mosseae and Glomus intraradices, but only very few genes were identified as being commonly regulated by all three AM fungi. Analysis of Pi concentrations in plants colonised by either of the three AM fungi revealed that this could be due to the higher Pi levels in plants inoculated by G. rosea compared with the other two fungi, explaining that numerous genes are commonly regulated by the interaction with G. rosea and by phosphate. Differential gene expression in roots inoculated with the three AM fungi was further studied by expression analyses of six genes from the phosphate transporter gene family in M. truncatula. While MtPT4 was induced by all three fungi, the other five genes showed different degrees of repression mirroring the functional differences in phosphate nutrition by G. rosea, G. mosseae and G. intraradices.
Publications

Hause, B.; Mrosk, C.; Isayenkov, S.; Strack, D.; Jasmonates in arbuscular mycorrhizal interactions Phytochemistry 68, 101-110, (2007) DOI: 10.1016/j.phytochem.2006.09.025

The mutualistic interaction between plants and arbuscular mycorrhizal (AM) fungi is believed to be regulated from the plant side among other signals by the action of phytohormones. Evidences for this are based mainly on application experiments and determination of phytohormone levels in AM roots by comparison to non-mycorrhizal roots. In case of jasmonates, additional proof is given by reverse genetic approaches, which led to first insights into their putative role in the establishment and functioning of the symbiosis. This review summarizes the current data about phytohormone action in AM roots and the role of jasmonates in particular.
Publications

Isayenkov, S.; Mrosk, C.; Stenzel, I.; Strack, D.; Hause, B.; Suppression of Allene Oxide Cyclase in Hairy Roots of Medicago truncatula Reduces Jasmonate Levels and the Degree of Mycorrhization with Glomus intraradices Plant Physiol. 139, 1401-1410, (2005) DOI: 10.1104/pp.105.069054

During the symbiotic interaction between Medicago truncatula and the arbuscular mycorrhizal (AM) fungus Glomus intraradices, an endogenous increase in jasmonic acid (JA) occurs. Two full-length cDNAs coding for the JA-biosynthetic enzyme allene oxide cyclase (AOC) from M. truncatula, designated as MtAOC1 and MtAOC2, were cloned and characterized. The AOC protein was localized in plastids and found to occur constitutively in all vascular tissues of M. truncatula. In leaves and roots, MtAOCs are expressed upon JA application. Enhanced expression was also observed during mycorrhization with G. intraradices. A partial suppression of MtAOC expression was achieved in roots following transformation with Agrobacterium rhizogenes harboring the MtAOC1 cDNA in the antisense direction under control of the cauliflower mosaic virus 35S promoter. In comparison to samples transformed with 35S∷uidA, roots with suppressed MtAOC1 expression exhibited lower JA levels and a remarkable delay in the process of colonization with G. intraradices. Both the mycorrhization rate, quantified by fungal rRNA, and the arbuscule formation, analyzed by the expression level of the AM-specific gene MtPT4, were affected. Staining of fungal material in roots with suppressed MtAOC1 revealed a decreased number of arbuscules, but these did not exhibit an altered structure. Our results indicate a crucial role for JA in the establishment of AM symbiosis.
Publications

Isayenkov, S.; Fester, T.; Hause, B.; Rapid determination of fungal colonization and arbuscule formation in roots of Medicago truncatula using real-time (RT) PCR J. Plant Physiol. 161, 1379-1383, (2004) DOI: 10.1016/j.jplph.2004.04.012

The quantifications of root colonization and symbiotic activity in the arbuscular mycorrhizal (AM) association of Medicago truncatula and Glomus intraradices were performed by quantitative polymerase chain reaction (real-time PCR). A strong correlation between fungal colonization of the root system and the amounts of fungal rDNA and rRNA were shown. In contrast, the transcript levels of the AM-specific phosphate transporter 4 from M. truncatula (MtPT4) correlate with arbuscule formation rather than with fungal colonization. These results suggest (i) that real-time PCR assay is a rapid, useful, and accurate method for the determination of arbuscular mycorrhizal features, (ii) that the amount of fungal rDNA or rRNA is a good parameter to estimate fungal colonization, and (iii) that it is necessary to evaluate the amount of other transcripts—like the MtPT4 transcript—to obtain additional information about the symbiotic state of the colonized root system.
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