Functional characterization of the Arabidopsis dynamin-related GTPases AtGBPL1 & 3

• Applicant: Professor Dr. Benedikt Kost
• Subject Area: Plant Cell and Developmental Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 551374878

Large GTPases of the dynamin-superfamily have diverse functions in important cellular processes including fission of endocytic vesicles from the plasma membrane, organelle fusion and division, ER morphogenesis and cell plate formation. Animal GBPs (Guanylate Binding Proteins), the most distantly related members of the dynamin-superfamily, are important regulators of immunity, although the molecular mechanisms underlying their functions are not well understood. Reports we and others have published since 2021 have initiated the functional characterization of AtGBPL1 and AtGBPL3, two closely related Arabidopsis GBP-like proteins. Our published and preliminary data establish that AtGBPL1 and AtGBPL3 are ubiquitously expressed and accumulate to highest levels in meristematic as well as in adjacent differentiating tissues. AtGBPL3 associates with the lamina on the inner surface of the nuclear envelope during interphase. After release from this structure during mitosis or upon pathogen infection, this protein condensates to large oligomers, possibly based on liquid-liquid-phase separation (LLPS). Interestingly, AtGBPL3 is required for processes as diverse as a) nuclear envelope formation during mitosis, b) nuclear morphogenesis, c) transcriptional repression in the nuclear periphery and d) defense gene activation upon infection. Data we reported demonstrate that AtGBPL3 specifically interacts with centromeric chromatin and with the lamina protein CRWN4. These data suggest that AtGBPL3 may have additional important functions a) in centromere scattering late during mitosis from the outer poles of newly forming daughter nuclei to uniformly distributed positions in the nuclear periphery and/or b) in stabilizing centromere positioning during interphase, which depends on CRWN-family proteins. Comparably little is currently known about the functions of AtGBPL1, which is structurally similar to AtBPL3 but unlike this protein lacks GTPase activity. We have shown that AtGBPL1 colocalizes with AtGBPL3 to the nuclear envelope during interphase. Furthermore, AtGBPL1 was reported to inhibit AtGBPL3-mediated defense gene activation. The research project proposed here has been designed to address to following specific questions: 1) How are the diverse established AtGBPL3 functions molecularly implemented and integrated with each other? 2) Does AtGBPL3 have additional functions in centromere positioning? 3) Does AtGBPL1 have other functions in addition to inhibiting AtGBPL3-mediated defense gene activation? Addressing these questions is expected to substantially advance our understanding of the roles played by AtGBPL1 and AtGBPL3 in fundamental cellular processes (cell division, regulation of gene expression), which are underlying plant development and defense.

• DFG Programme: Research Grants