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Publications - Cell and Metabolic Biology

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Publications

Akaberi, S., Wang, H., Claudel, P., Riemann, M., Hause, B., Hugueney, P. & Nick, P. Grapevine fatty acid hydroperoxide lyase generates actin-disrupting volatiles and promotes defence-related cell death J Exp Bot 69, 2883-2896, (2018) DOI: 10.1093/jxb/ery133

Fatty acid hydroperoxides can generate short-chained volatile aldehydes that may participate in plant defence. A grapevine hydroperoxide lyase (VvHPL1) clustering to the CYP74B class was functionally characterized with respect to a role in defence. In grapevine leaves, transcripts of this gene accumulated rapidly to high abundance in response to wounding. Cellular functions of VvHPL1 were investigated upon heterologous expression in tobacco BY-2 cells. A C-terminal green fluorescent protein (GFP) fusion of VvHPL1 was located in plastids. The overexpression lines were found to respond to salinity stress or the bacterial elicitor harpin by increasing cell death. This signal-dependent mortality response was mitigated either by addition of exogenous jasmonic acid or by treatment with diphenyleneiodonium (DPI), an inhibitor of NADPH oxidases. By feeding different substrates to recombinantly expressed enzyme, VvHPL1 could also be functionally classified as true 13-HPL. The cognate products generated by this 13-HPL were cis-3-hexenal and trans-2-hexenal. Using a GFP-tagged actin marker line, one of these isomeric products, cis-3-hexenal, was found specifically to elicit a rapid disintegration of actin filaments. This response was not only observed in the heterologous system (tobacco BY-2), but also in a grapevine cell strain expressing this marker, as well as in leaf discs from an actin marker grape used as a homologous system. These results are discussed in the context of a role for VvHPL1 in a lipoxygenase-dependent signalling pathway triggering cell death-related defence that bifurcates from jasmonate-dependent basal immunity.
Publications

Gelová, Z., ten Hoopen, P., Novák, O., Motyka, V., Pernisová, M., Dabravolski, S., Didi, V., Tillack, I., Oklešťková, J., Strnad, M., Hause, B., Haruštiaková, D., Conrad, U., Janda, L. & Hejátko, J. Antibody-mediated modulation of cytokinins in tobacco: organ-specific changes in cytokinin homeostasis. J Exp Bot 69, 441-454, (2018) DOI: 10.1093/jxb/erx426

Cytokinins comprise a group of phytohormones with an organ-specific mode of action. Although the mechanisms controlling the complex networks of cytokinin metabolism are partially known, the role of individual cytokinin types in the maintenance of cytokinin homeostasis remains unclear. Utilizing the overproduction of single-chain Fv antibodies selected for their ability to bind trans-zeatin riboside and targeted to the endoplasmic reticulum, we post-synthetically modulated cytokinin ribosides, the proposed transport forms of cytokinins. We observed asymmetric activity of cytokinin biosynthetic genes and cytokinin distribution in wild-type tobacco seedlings with higher cytokinin abundance in the root than in the shoot. Antibody-mediated modulation of cytokinin ribosides further enhanced the relative cytokinin abundance in the roots and induced cytokinin-related phenotypes in an organ-specific manner. The activity of cytokinin oxidase/dehydrogenase in the roots was strongly up-regulated in response to antibody-mediated formation of the cytokinin pool in the endoplasmic reticulum. However, we only detected a slight decrease in the root cytokinin levels. In contrast, a significant decrease of cytokinins occurred in the shoot. We suggest the roots as the main site of cytokinin biosynthesis in tobacco seedlings. Conversely, cytokinin levels in the shoot seem to depend largely on long-range transport of cytokinin ribosides from the root and their subsequent metabolic activation.

Publications

Weier, D., Thiel, J., Kohl, S., Tarkowská, D., Strnad, M., Schaarschmidt, S., Weschke, W., Weber, H. & Hause, B. Gibberellin-to-abscisic acid balances govern development and differentiation of the nucellar projection of barley grains. J Exp Bot 65, 5291-5304, (2014) DOI: 10.1093/jxb/eru289

In cereal grains, the maternal nucellar projection (NP) constitutes the link to the filial organs, forming a transfer path for assimilates and signals towards the endosperm. At transition to the storage phase, the NP of barley (Hordeum vulgare) undergoes dynamic and regulated differentiation forming a characteristic pattern of proliferating, elongating, and disintegrating cells. Immunolocalization revealed that abscisic acid (ABA) is abundant in early non-elongated

but not in differentiated NP cells. In the maternally affected shrunken-endosperm mutant seg8, NP cells did not elongate and ABA remained abundant. The amounts of the bioactive forms of gibberellins (GAs) as well as their biosynthetic precursors were strongly and transiently increased in wild-type caryopses during the transition and early storage phases. In seg8, this increase was delayed and less pronounced together with deregulated gene expression

of specific ABA and GA biosynthetic genes. We concluded that differentiation of the barley NP is driven by a distinct and specific shift from lower to higher GA:ABA ratios and that the spatial–temporal change of GA:ABA balances is required to form the differentiation gradient, which is a prerequisite for ordered transfer processes through the NP. Deregulated ABA:GA balances inseg8 impair the differentiation of the NP and potentially compromise transfer of signals and assimilates, resulting in aberrant endosperm growth. These results highlight the impact of hormonal balances on the proper release of assimilates from maternal to filial organs and provide new insights into maternal effects on endosperm differentiation and growth of barley grains.

Publications

Wasternack, C. & Hause, B. Emerging complexity: jasmonate-induced volatiles affect parasitoid choice J Exp Bot 60, 2451-2453, (2009) DOI: 10.1093/jxb/erp197

Plant responses to specific environmental stimuli at the molecular and genetic levels have been widely reported in recent decades, mainly as a consequence of the availability of new laboratory techniques. However, understanding the complex implications of these observations at the ecosystem level remains one of the greatest challenges facing plant science today. Recently, new experimental strategies have been designed to address complex interactions. For example, combinations of different insects have been used to study insect–plant interactions (Dicke et al., 2009) as well as parallel analysis of the responses to different types of pathogen which reflect more closely the conditions encountered in natural ecosystems (Pieterse et al., 2009).

In this issue, the two papers by Bruinsma and colleagues also address such complex issues; the detailed analysis of plant responses to different herbivores and JA application are documented, and the responses of parasitic wasps that attack the herbivores are recorded. The authors’ experimental design and interpretation of the results highlight the importance of understanding the complexity of plant responses in the context of a whole ecosystem.

In the last two decades, interest in plant–insect interactions using ecological, chemical, and molecular approaches has increased dramatically. Direct defence reactions of plants, such as the production of toxins or deterrent proteins like proteinase inhibitors, as well as indirect defence reactions, have been identified showing that the effectiveness of the natural enemies of attackers can be altered. In the latter case, the induced release of volatiles is a common phenomenon leading to the attraction of carnivores. Plants attacked by herbivores respond with the establishment of a chemical phenotype, releasing volatiles into the atmosphere that include terpenoids, phenylpropanoids or fatty acid-derived green leaf volatiles. The detailed composition of the volatile blend is insect-specific and depends on the type of attacker (e.g. chewing or sucking … 

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