Identifizierung und Charakterisierung von Genen, die regulatorische oder strukturelle Plasmodesmataproteine kodieren
Final Report Abstract
The aim of the project was to study plasmodesmata in Arabidopsis. A first approach was the identification of Arabidopsis mutants with altered plasmodesmata. We performed an EMS mutagenesis of Arabidopsis plants which expressed GFP in single cells and screened for mutants with changes in GFP distribution. However, we could not isolate a single mutant line which carried a monogenic mutation which led to altered cell-to-cell movement of GFP so far. In a second approach we studied the presence of functional plasmodesmata in the phloem unloading domain in ovules of Arabidopsis thaliana. We could show that the mode of phloem unloading switches two times during ovule development. Very early during ovule development functional plasmodesmata are present which mediate symplastic phloem unloading. In contrast, symplastic unloading could not be observed in mature ovules, where GFP and also the small tracer HPTS accumulated in the sieve element / companion cell complexes. Another change back to a symplastic mode of phloem unloading was observed after pollination. In fertilized flowers, GFP could move from the phloem into cells of the integuments. Consistent with these results we could show that a strong labeling of plasmodesmata with MP17-GFP, which binds secondary plasmodesmata, occurs in phloem unloading domains of pollinated ovaries but not of mature ovules. All together our data proved that the presence of plasmodesmata and the mode of phloem unloading differ not only between various sink tissues but also during different developmental stages and that symplasmic connectivity is highly regulated. In a third project we analyzed changes in frequency and size exclusion limit of plasmodesmata during seedling development. We used PLASMODESMATA LOCATED PROTEIN 1 (PDLP1) fused to GFP to label primary plasmodesmata and MOVEMENT PROTEIN MP17 from potato leaf roll virus to mark secondary plasmodesmata. We could show that the quiescent center in the root meristem is highly connected to adjacent initials by numerous (most probably secondary) plasmodesmata. To investigate the size exclusion limit of plasmodesmata in root tips we expressed fluorescent proteins of different size in specific root cell layers. First analyses of transgenic lines showed that the tangential movement of fluorescent proteins is stronger than the radial movement. This indicated that the connectivity between cells of one cell layer is higher than the connectivity between two different cell layers (as for example stele and endodermis). We also could show that the quiescent center is highly connected to cortex/endodermis initials. In addition we proved an inducible expression system to be highly suitable for temporal resolution of movement processes. The observed results will be published after further completing analyses of protein movement in the root tip of Arabidopsis using an inducible expression system.
Publications
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(2011). A dual switch in phloem unloading during ovule development. Protoplasma 248: 225-235
Werner D, Gerlitz N, Stadler R
