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Publikation

Abel, S.; Theologis, A.; Odyssey of Auxin Cold Spring Harb. Perspect. Biol. 2, a004572, (2010) DOI: 10.1101/cshperspect.a004572

The history of plant biology is inexorably intertwined with the conception and discovery of auxin, followed by the many decades of research to comprehend its action during growth and development. Growth responses to auxin are complex and require the coordination of auxin production, transport, and perception. In this overview of past auxin research, we limit our discourse to the mechanism of auxin action. We attempt to trace the almost epic voyage from the birth of the hormonal concept in plants to the recent crystallographic studies that resolved the TIR1-auxin receptor complex, the first structural model of a plant hormone receptor. The century-long endeavor is a beautiful illustration of the power of scientific reasoning and human intuition, but it also brings to light the fact that decisive progress is made when new technologies emerge and disciplines unite.
Publikation

Floß, D. S.; Hause, B.; Lange, P. R.; Küster, H.; Strack, D.; Walter, M. H.; Knock-down of the MEP pathway isogene 1-deoxy-d-xylulose 5-phosphate synthase 2 inhibits formation of arbuscular mycorrhiza-induced apocarotenoids, and abolishes normal expression of mycorrhiza-specific plant marker genes Plant J. 56, 86-100, (2008) DOI: 10.1111/j.1365-313X.2008.03575.x

The first step of the plastidial methylerythritol phosphate (MEP) pathway is catalyzed by two isoforms of 1‐deoxy‐d‐ xylulose 5‐phosphate synthase (DXS1 and DXS2). In Medicago truncatula , MtDXS1 and MtDXS2 genes exhibit completely different expression patterns. Most prominently, colonization by arbuscular mycorrhizal (AM) fungi induces the accumulation of certain apocarotenoids (cyclohexenone and mycorradicin derivatives) correlated with the expression of MtDXS2 but not of MtDXS1. To prove a distinct function of DXS2, a selective RNAi approach on MtDXS2 expression was performed in transgenic hairy roots of M. truncatula. Repression of MtDXS2 consistently led to reduced transcript levels in mycorrhizal roots, and to a concomitant reduction of AM‐induced apocarotenoid accumulation. The transcript levels of MtDXS1 remained unaltered in RNAi plants, and no phenotypical changes in non‐AM plants were observed. Late stages of the AM symbiosis were adversely affected, but only upon strong repression with residual MtDXS2‐1 transcript levels remaining below approximately 10%. This condition resulted in a strong decrease in the transcript levels of MtPT4 , an AM‐specific plant phosphate transporter gene, and in a multitude of other AM‐induced plant marker genes, as shown by transcriptome analysis. This was accompanied by an increased proportion of degenerating and dead arbuscules at the expense of mature ones. The data reveal a requirement for DXS2‐dependent MEP pathway‐based isoprenoid products to sustain mycorrhizal functionality at later stages of the symbiosis. They further validate the concept of a distinct role for DXS2 in secondary metabolism, and offer a novel tool to selectively manipulate the levels of secondary isoprenoids by targeting their precursor supply.
Publikation

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.
Publikation

Hause, B.; Maier, W.; Miersch, O.; Kramell, R.; Strack, D.; Induction of Jasmonate Biosynthesis in Arbuscular Mycorrhizal Barley Roots Plant Physiol. 130, 1213-1220, (2002) DOI: 10.1104/pp.006007

Colonization of barley (Hordeum vulgare cv Salome) roots by an arbuscular mycorrhizal fungus, Glomus intraradices Schenck & Smith, leads to elevated levels of endogenous jasmonic acid (JA) and its amino acid conjugate JA-isoleucine, whereas the level of the JA precursor, oxophytodienoic acid, remains constant. The rise in jasmonates is accompanied by the expression of genes coding for an enzyme of JA biosynthesis (allene oxide synthase) and of a jasmonate-induced protein (JIP23). In situ hybridization and immunocytochemical analysis revealed that expression of these genes occurred cell specifically within arbuscule-containing root cortex cells. The concomitant gene expression indicates that jasmonates are generated and act within arbuscule-containing cells. By use of a near-synchronous mycorrhization, analysis of temporal expression patterns showed the occurrence of transcript accumulation 4 to 6 d after the appearance of the first arbuscules. This suggests that the endogenous rise in jasmonates might be related to the fully established symbiosis rather than to the recognition of interacting partners or to the onset of interaction. Because the plant supplies the fungus with carbohydrates, a model is proposed in which the induction of JA biosynthesis in colonized roots is linked to the stronger sink function of mycorrhizal roots compared with nonmycorrhizal roots.
Publikation

Morgan, K. E.; Zarembinski, T. I.; Theologis, A.; Abel, S.; Biochemical characterization of recombinant polypeptides corresponding to the predicted βαα fold in Aux/IAA proteins FEBS Lett. 454, 283-287, (1999) DOI: 10.1016/S0014-5793(99)00819-4

The plant hormone indoleacetic acid (IAA or auxin) transcriptionally activates a select set of early genes. The Auxl IAA class of early auxin-responsive genes encodes a large family of short-lived, nuclear proteins. Aux/IAA polypeptides homo-and heterodimerize, and interact with auxin-response transcription factors (ARFs) via C-terminal regions conserved in both protein families. This shared region contains a predicted βαα motif similar to the prokaryotic β-Ribbon DNA binding domain, which mediates both protein dimerization and DNA recognition. Here, we show by circular dichroism spectroscopy and by chemical cross-linking experiments that recombinant peptides corresponding to the predicted βαα region of three Aux/IAA proteins from Arabidopsis thaliana contain substantial α-helical secondary structure and undergo homo- and heterotypic interactions in vitro. Our results indicate a similar biochemical function of the plant βαα domain and suggest that the βαα fold plays an important role in mediating combinatorial interactions of Aux/IAA and ARF proteins to specifically regulate secondary gene expression in response to auxin.
Publikation

Ziegler, J.; Vogt, T.; Miersch, O.; Strack, D.; Concentration of Dilute Protein Solutions Prior to Sodium Dodecyl Sulfate–Polyacrylamide Gel Electrophoresis Anal. Biochem. 250, 257-260, (1997) DOI: 10.1006/abio.1997.2248

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Publikation

Wong, L. M.; Abel, S.; Shen, N.; de la Foata, M.; Mall, Y.; Theologis, A.; Differential activation of the primary auxin response genes, PS-IAA4/5 and PS-IAA6, during early plant development Plant J. 9, 587-599, (1996) DOI: 10.1046/j.1365-313X.1996.9050587.x

The plant growth hormone auxin typified by indoleacetic acid (IAA) transcriptionally activates early genes in pea, PS‐IAA4/5 and PS‐IAA6 , that are members of a multigene family encoding short‐lived nuclear proteins. To gain first insight into the biological role of PS‐IAA4/5 and PSIAA6 , promoter‐β‐glucuronidase (GUS) gene fusions were constructed and their expression during early development of transgenic tobacco seedlings was examined. The comparative analysis reveals spatial and temporal expression patterns of both genes that correlate with cells, tissues, and developmental processes known to be affected by auxin. GUS activity in seedlings of both transgenic lines is located in the root meristem, sites of lateral root initiation and in hypocotyls undergoing rapid elongation. In addition, mutually exclusive cell‐specific expression is evident. For instance, PS‐IAA4/5—GUS but not PS‐IAA6—GUS is expressed in root vascular tissue and in guard cells, whereas only PS‐IAA6—GUS activity is detectable in glandular trichomes and redistributes to the elongating side of the hypocotyl upon gravitropic stimulation. Expression of PS‐IAA4/5 and PS‐IAA6 in elongating, dividing, and differentiating cell types indicates multiple functions during development. The common and yet distinct activity patterns of both genes suggest a combinatorial code of spatio‐temporal co‐expression of the various PS‐IAA4/ 5‐like gene family members in plant development that may mediate cell‐specific responses to auxin.
Publikation

Abel, S.; Theologis, A.; Early Genes and Auxin Action Plant Physiol. 111, 9-17, (1996) DOI: 10.1104/pp.111.1.9

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Publikation

Abel, S.; Ballas, N.; Wong, L.-M.; Theologis, A.; DNA elements responsive to auxin BioEssays 18, 647-654, (1996) DOI: 10.1002/bies.950180808

Genes induced by the plant hormone auxin are probably involved in the execution of vital cellular functions and developmental processes. Experimental approaches designed to elucidate the molecular mechanisms of auxin action have focused on auxin perception, genetic dissection of the signaling apparatus and specific gene activation. Auxin‐responsive promoter elements of early genes provide molecular tools for probing auxin signaling in reverse. Functional analysis of several auxin‐specific promoters of unrelated early genes suggests combinatorial utilization of both conserved and variable elements. These elements are arranged into autonomous domains and the combination of such modules generates uniquely composed promoters. Modular promoters allow for auxin‐mediated transcriptional responses to be revealed in a tissue‐ and development‐specific manner.
  • Die Leibniz-Gemeinschaft
  • Digitalisierung in der Landwirtschaft
  • Martin-Luther Universität Halle
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