In vascular plants, long-distance transport of photoassimilates is accomplished by the sieve tubes in the phloem. Dicotyledonous plants have evolved a highly specialized wound sealing mechanism that prevents the loss of sugars upon injury. This mechanism based on P-proteins (phloem proteins), which block the flow of assimilates by plugging sieve plates. We are studying different aspects of P-protein biology including molecular phylogeny and physiology, functional genomics and biophysics with a special focus on forisomes – a unique contractile P-protein type from legumes.
The ‘Sieve Element Occlusion’ (SEO) gene family
SEO genes are widely distributed in dicotyledonous plants and also include genes encoding forisome components. We are presently characterizing the evolution of SEO genes and could identify several conserved motifs in SEO proteins.
Phloem-specific expression of SEO genes.
Expression of SEO genes encoding forisomes (SEO-F; sieve element occlusion by forisomes) was shown to be restricted to immature sieve elements, where forisomes first appear during plant development. In ongoing studies, we concentrate our work on the identification and characterization of gene-regulatory sequences and factors controlling the spatiotemporal activity of SEO-F promoters with emphasis on phloem development.
Forisome reaction type and applications
The regulatory properties of forisomes are one of the most remarkable recent discoveries in the field of long-distance transport in plants. When stimulated by changes in Ca2+ levels or pH, forisomes instantaneously switch between a dispersed and a condensed conformation. We could show that expression of SEO-F1 and SEO-F4 from Medicago truncatula in tobacco and yeast resulted in the production of spindle-shaped artificial forisomes that can undergo reversible conformational changes similar to native forisomes. Artificial forisomes will assist further studies on forisome’s structure and reactivity and will provide an excellent basis for the utilization of forisomes as biomaterials in medicine, material science and biochemistry.