Analysis and reconstitution of regulatory networks governing epidermal differentiation and polar root hair growth

• Applicant: Professor Dr. Jörg Kudla
• Subject Area: Plant Cell and Developmental Biology
• Term: since 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 264387517

Tip-focused growth represents an important mechanism to establish cellular polarity and is a fundamental process that underlies the growth of neuronal axon, fungal hyphae and plant root hairs. Root hairs are cylindrical shaped cellular protuberances of specialized epidermal cells. Polar tip growth of root hairs requires tight coordination and regulation of cytoskeleton dynamics, vesicle transport and ion fluxes. In root hairs a high-tip Ca2+ gradient has been shown to be essential for polar growth. Oscillatory Ca2+ increases are superimposed on this Ca2+ gradient and are likely to coordinate oscillatory tip growth and oscillatory fluctuations of reactive oxygen species (ROS) concentrations and pH values. The long-term goal of this project is to understand the molecular components and mechanisms underlying polar RH tip growth. Moreover, we intend to reconstitute such an oscillating network. Our preliminary data as well as published findings indicate that Ca2+ activated CBL/CIPK complexes and CDPKs simultaneously activate NADPH oxidases. Moreover, accumulating evidence also suggests Ca2+ independent phosphorylation as an alternative means of NADPH oxidase activation and a role of specific phosphatases in counteracting such activation. In this project we want to elucidate how exactly the different components of signaling network function and how they are dynamically interconnected and how quantitative changes in Ca2+ parameters govern information processing in root hairs. Considering our new findings and results obtained during the last years, we now specifically want to focus on the following research aims: (i) Explore the mechanisms and components contributing to the generation of the tip-focused Ca2+ gradient and Ca2+ oscillations in RHs. (ii) Elucidate the role of Ca2+ dependent phosphorylation in modulating RbohC activity. (iii) Investigate a potential contribution of Ca2+-independent phosphorylation to the regulation of RbohC. (iv) Explore the currently elusive components and mechanisms that bring about the required deactivation of RbohC in RHs. By combining the insights gained from project areas (i) – (iv), we subsequently intend to (v) characterize the complex interplay of these kinases and phosphatases in regulating RbohC and (vi) initiate the reconstitution of a regulatory network underlying the formation of Ca2+ oscillations and ROS signals heterologously in HEK293T cells. Complementary to these approaches, we intend to further advance our investigations of second messenger dynamics in RHs and continue to identify novel components that contribute to these processes. Collectively, our approaches should reveal detailed and fundamental insights of the complex interplay of these signaling components in growing RH.

• DFG Programme: Research Grants