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 across
eukaryotes. Its role is the polymerization of actin filaments from monomeric actin. In
amoebae and animal cells, the ARP2/3 complex is crucial for the formation of lamellipodia
and 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 in
plants must play a different role than in cell motility. During my PhD, I studied the role of
the ARP2/3 complex in plants in various contexts of plant cell biology, and I participated
in the research of this complex on several levels, from the role of individual subunits in
the functioning of the complex to its interaction with the cytoskeleton and cell organelles
and its influence on cell growth and morphogenesis. We described new double mutants in
both ARPC1A and ARPC1B and revealed the ARPC3 subunit has different importance in
the ARP2/3 complex, depending on the cellular context, specifically in vegetative and
generative tissues, indicating a specific role of this subunit in plant ARP2/3 complex. We
also demonstrated a unique role of the ARPC2 subunit, which interacts not only with actin
filaments but also with microtubules, which is significant considering the role of both in
plant cell morphogenesis. We studied how the ARP2/3 complex regulates the actin
cytoskeleton, together formin FH1, and how that affects cell morphogenesis. Results from
our research of ARP2/3 in pollen tubes indicate that it may be involved in specific
modifications in cell wall pectins through endocytosis of pectin-modifying enzymes. This
mechanism could explain other phenotypes of ARP2/3 complex mutants like problems in
cell morphogenesis and adhesion. We also discovered that the ARP2/3 complex is
responsible for the autophagic degradation of peroxisomes in plant cells, which further
connects the role of the plant ARP2/3 complex to membranes and their remodeling.
Throughout my dissertation, these studies collectively highlight the multifaceted role of
the ARP2/3 complex in plant cell biology, describing how its involvement in cytoskeletal
dynamics affects plant cell morphogenesis and adhesion, apical growth of pollen tubes,
and also endocytosis and pexophagy. Finally, I present a hypothetical universal
framework explaining how plant ARP2/3 complex may be involved in all these seemingly
unrelated processes.