Nicole van ‘t Wout Hofland : The origin and evolution of vascular tissue regulators

The development of vascular tissues is considered as one of the major steps in the evolution of land plants, allowing the transport of water, nutrients, hormones and other regulators in larger structures. Recently, TARGET OF MONOPTEROS5 (TMO5) and its homologs were shown to interact with LONESOME HIGHWAY (LHW) and its homologs. These TMO5/LHW heterodimers are bHLH transcription factors and control the number of cell files in the vascular tissues by triggering periclinal (longitudinal) cell divisions through local production of the phytohormone cytokinin (CK).

During my project, we investigate to what extent the recruitment of TMO5 and LHW has contributed to complexity of the vascular tissue over evolution. In other words, we are trying to find out if the TMO5/LHW dimer developed before, after, or simultaneously with complex vascular tissue. In addition, we would like to know if there are any ancestral functions of TMO5 and/or LHW, as a complex or as monomer or homodimer.

Bioinformatical analysis coupled to experimental work identified orthologs of TMO5 and LHW in a range of plant species. TMO5-like proteins were found in non-vascular plants like the liverwort Marchantia polymorpha (Mp). In contrast, LHW orthologs were solely identified in vascular plants. Ergo, LHW seems to be less conserved than TMO5. However, many questions remain unanswered. In order to answer some of them we will use a combination of some bioinformatics, molecular biology (cloning), Bimolecular fluorescence complementation (BiFC), Number and Brigtness method and other microscopy techniques.

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