Thursday 26.9.2024 The defense will take place at the Department of Experimental Plant Biology on Friday, September 27th 2024, 10:30 a.m. in the KFR seminar room (213), Viničná 5, 2nd floor, Prague. Guests can join us online via the seminar link: meet.google.com/qhf-etyu-sna Mgr. Jan Martinek student of 9th grade DSP EPB, Fac. Sci., CUNI Thesis title: Specific functions of ARP2/3 complex in plants Supervisor: RNDr. Kateřina Schwarzerová, Ph.D. Reviewers: prof. Mgr. Miroslav Ovečka, Ph.D. (Palacký University, Olomouc) & Mgr. Jozef Mravec, Ph.D. (Institute of Plant Genetics and Biotechnology, Nitra) Abstract: The ARP2/3 complex is a heteroheptameric protein complex conserved acrosseukaryotes. Its role is the polymerization of actin filaments from monomeric actin. Inamoebae and animal cells, the ARP2/3 complex is crucial for the formation of lamellipodiaand pseudopodia, which are plasma membrane protrusions essential for cell motility.Given the presence of a cell wall, it is evident that the conserved ARP2/3 complex inplants must play a different role than in cell motility. During my PhD, I studied the role ofthe ARP2/3 complex in plants in various contexts of plant cell biology, and I participatedin the research of this complex on several levels, from the role of individual subunits inthe functioning of the complex to its interaction with the cytoskeleton and cell organellesand its influence on cell growth and morphogenesis. We described new double mutants inboth ARPC1A and ARPC1B and revealed the ARPC3 subunit has different importance inthe ARP2/3 complex, depending on the cellular context, specifically in vegetative andgenerative tissues, indicating a specific role of this subunit in plant ARP2/3 complex. Wealso demonstrated a unique role of the ARPC2 subunit, which interacts not only with actinfilaments but also with microtubules, which is significant considering the role of both inplant cell morphogenesis. We studied how the ARP2/3 complex regulates the actincytoskeleton, together formin FH1, and how that affects cell morphogenesis. Results fromour research of ARP2/3 in pollen tubes indicate that it may be involved in specificmodifications in cell wall pectins through endocytosis of pectin-modifying enzymes. Thismechanism could explain other phenotypes of ARP2/3 complex mutants like problems incell morphogenesis and adhesion. We also discovered that the ARP2/3 complex isresponsible for the autophagic degradation of peroxisomes in plant cells, which furtherconnects the role of the plant ARP2/3 complex to membranes and their remodeling.Throughout my dissertation, these studies collectively highlight the multifaceted role ofthe ARP2/3 complex in plant cell biology, describing how its involvement in cytoskeletaldynamics affects plant cell morphogenesis and adhesion, apical growth of pollen tubes,and also endocytosis and pexophagy. Finally, I present a hypothetical universalframework explaining how plant ARP2/3 complex may be involved in all these seeminglyunrelated processes.