Intercellular signaling in metaphloem development

• Applicant: Dr. Moritz Graeff
• Subject Area: Plant Cell and Developmental Biology
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 327627339

During their evolution, plants developed a complex transport system to facilitate the exchange of water, nutrients and signalling molecules between their different organs. Within this vasculature system, sugars and signalling molecules are transported in the phloem, a tissue that allows directed transport of these molecules. Phloem cells originate from stem cells in the shoot or root apical meristem. The fate the daughter cell of a stem cell adapts depends highly on its positional context. How such positional information is generated, transmitted and perceived is a key question for developmental biologists. There are two different types of phloem tissues that derive from the same stem cell files. The protophloem, important during initial development, has a major role in the transport of hormones towards the meristematic regions. The other phloem tissue type is the metaphloem, the major tissue for the long distance transport of sugars and signalling molecules between differentiated parts of the plant. In the last years some of the factors controlling protophloem development have been identified and it became evident that intercellular signalling processes play a central role in this process. How these factors interact and influence the development of the vasculature remains the subject of intense research. As little we know about them yet, even less is known about the metaphloem. This project aims to characterize the metaphloem tissue in Arabidopsis roots and to identify factors that regulate its development. The first step of this project is therefore a detailed histological characterization of this tissue and its development in wildtype plants and different mutants with phloem defects.Both phloem cell files originate from the same periclinal division but while the protophloem continues its differentiation rapidly, the differentiation of the metaphloem is delayed. Signals produced in the protophloem might actively suppress the differentiation of its neighbouring cell file. To test this hypothesis, I plan to investigate the role of signalling peptides produced in the protophloem as well as the effects of a disturbed cell-to-cell communication on metaphloem development. The factors known to be important for protophloem development are not directly affecting metaphloem development, but it is conceivable that similar factors are important here. I plan to study the role of so far uncharacterized homologs of such factors in the metaphloem. Finally, I will perform a mutagenesis screen to identify genes important for metaphloem development. Overall, the project aims to provide a better understanding of the metaphloem and its development. The different targeted and untargeted approaches to the project will reveal factors influencing its development and help to understand the underlying network. In addition will the project gain new insights into intercellular signalling in the root and plant development in general.

• DFG Programme: Research Fellowships
• International Connection: Switzerland
• Host: Professor Dr. Christian Hardtke