Determining mechanisms of phloem formation

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The phloem tissue is the main conduit for transporting organic matter including carbohydrates, hormones and other signaling molecules throughout the plant body. Driven by this central role for plant growth and physiology, the phloem has emerged in recent years as a paradigm for plant tissue formation. Previously, we discovered that the nuclear SUPPRESSOR OF MAX2 1-LIKE 3 (SMXL3), SMXL4 and SMXL5 proteins are key regulators of phloem formation acting at early stages, presumably, by establishing a phloem-specific chromatin profile. However, insight into the molecular role of SMXL proteins is still limited including knowledge of their effect on nuclear signatures, protein binding partners and putative gene targets. In the context of this project, we will concentrate on the role of SMXL5 hypothesizing that SMXL5 forms protein complexes in nuclei of future phloem cells establishing chromatin signatures essential for phloem specification. We will test this hypothesis by identifying interacting proteins in planta and verifying the relevance of these interactions, and by revealing tissue-specific chromatin signatures and their dependence on SMXL5-associated proteins. Following this strategy, the project makes use of highly instructive read-outs for the SMXL5 function and combines the benefits of orthogonal biochemical and genetic experimental approaches. We expect that, thereby, the project will not only deepen our understanding of the regulatory principles of tissue specification but also reveal the action mode of a group of intriguing developmental regulators.