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Hannah Elisa Krawczyk ( Münster University)

Hannah Elisa Krawczyk's Master thesis was awarded with the Prize for the Best Plant Science Master Thesis, which was carried out at xxUniversity in the year 2017

Title of awarded thesis

"Influence of complex-type N-glycosylation on brassinosteroid signaling in Arabidopsis thaliana"

Hannah Elisa Krawczyk attempts to elucidate specific functions of N-glycosylated proteins in plants. She now found a correlation between the inability to form complex-type or hybrid-type N-glycans in the Golgi apparatus and an altered sensitivity towards the two phytohormones brassinolide (BL) and abscisic acid (ABA).

Complex Glycan-Less1 (CGL1, in Arabidopsis also N-acetylglucosaminyltransferase I, GNTI), a membrane-bound enzyme that initiates complex-type N-glycan formation on secreted and membrane-bound glycoproteins in the Golgi apparatus, was already discovered more than 20 years ago (von Schaewen et al., 1993). However to date, the exact role and function of complex-type N-glycans in plants is still not known. Proteome analyses of cgl1-2 seedlings (unpublished data) revealed a strong deregulation of the plasma membrane-localized receptor kinase Brassinosteroid (BR) Insensitive1 (BRI1), which contains several N-glycosylation sites in its ectodomain. Therefore responses to brassinolide (BL, the most active BR) and/or its antagonist abscisic acid (ABA) were analyzed during seed germination and seedling establishment by comparing dormancy release, germination capacity and hypocotyl elongation of wild-type (WT) versus cgl1-2 mutant plants under different conditions and treatments. We found strong evidence, that cgl1-2 is impaired in proper BR-signal transduction, showing hypo-sensitivity towards exogenous BL and hyper-sensitivity towards exogenous as well as endogenous ABA. Compared to wild-type plants, cgl1-2 mutants displayed dose-dependent defects in seedling establishment after exogenous ABA application, while germination sensu stricto (radicle protrusion) was not significantly affected (Figure 1 a,b,f). It is known that ABA-inhibited seed germination can be rescued by BL application. Indeed, low epi-BL concentrations failed to rescue mutant seedling establishment, while WT seedling establishment was restored (Figure 1 c). Also, seedling establishment of cgl1-2 was more severely inhibited by the BR synthesis inhibitor Brassinazole (BRZ; Figure 1 e). These results demonstrate an important role of complex-type N-glycan decoration for BRI1, which should be analysed further.

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Hannah Elisa Krawczyk conducted this work at the Institute for Biology and Biotechnology of Plants (IBBP), Molecular Physiology of Plants, Westfälische Wilhelms-Universität Münster in the group of Professor Dr. Dr. Antje von Schaewen. She now completes her studies at the Albrecht-von-Haller-Institute for plant sciences at Georg-August-Universität Göttingen.


Figure 1a) and 1b): ABA dose-response. ABA-dose response analyses of cgl1-2 and WT seeds in regard to radicle protrusion (a) and cotyledon greening (b) were performed. There were no significant differences between wildtype and cgl1-2 seeds at 0, 0.25, 0.5, 1 or 2.5 µM ABA in terms of radicle protrusion. In terms of seedling establishment, cgl1-2 seeds were significantly hyper-sensitive towards 0.25 and 0.5 µM ABA. Figure 1c) – 1e): Seedling establishment restoration. Influence of different treatments on WT and cgl1-2 seedling establishment was analysed. Neither mock (solvent) treatment (d), nor different concentrations of epi-BL alone (d) or Brassinazole (BRZ) alone (e) affected seedling establishment. 0.5 µM ABA inhibited seedling establishment much more severely in cgl1-2 than in the wildtype (b, c and e). Additional application of 0.5 µM ABA and increasing concentrations of epi-BL led to stepwise increase in seedling establishment of wildtype, but not of cgl1-2 (c). Only at 0.5 µM epi-BL did cgl1-2 seeds react towards exogenous epi-BL and seedling establishment was rescued. Additional application of 0.5 µM ABA and 0.25 µM BRZ led to further inhibition of seedling establishment in the wildtype and in cgl1-2 (e). Figure 1f): Cotyledon greening at 0.5 µM ABA. Seedling establishment of WT (left) and cgl1-2 seedlings on 0.5 µM ABA germinated on filter papers in moist chamber is shown. In the wildtype, most germinated seedlings established seedlings. In cgl1-2, most seeds, although germinated, stopped development prior to proper seedling establishment. Graph: Hannah Elisa Krawczyk, Westfälische Wilhelms-Universität Münster