Collaborative Research: Molecular mechanisms governing the cytoskeleton-mediated motility and distribution of peroxisomes and mitochondria in plants

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This research is aimed at addressing a fundamental question in cell biology that is directly associated with growth and reproduction of plants, including crops. Plant cells mobilize their highly dynamic subcellular compartments, known as organelles, to fulfill physiological functions in growth and development. This project will uncover the poorly understood mechanisms by which organelles move and distribute along molecular tracks called actin filaments within plant cells in response to internal and external signals. The focus will be on peroxisomes and mitochondria, two organelles that are physically and biochemically connected and essential for energy metabolism and survival of plants. The molecular machinery responsible for the motility and distribution of these two types of organelles will be dissected, using the small mustard plant Arabidopsis. Knowledge gained will provide fundamental insights into the principles associated with the motility of plant organelles, thereby giving perspectives on how these molecular machineries evolved. In addition, the project will train graduate and undergraduate students in modern biological skills. Hands-on research experience will be provided to first-year undergraduate students in the classroom with the goal of retaining them in science majors. Discovery-based summer trainings will be provided to undergraduates in molecular biology, genetics, cell biology, physiology and computational biology in order to prepare them for a scientific career or advanced training after graduation. Cytoskeleton-dependent active movement and distribution of organelles are fundamentally significant for cell growth, division, and signaling. However, how organelles recruit cytoskeletal motor proteins for their directional transport along the cytoskeletal tracks is complex and often under debate. This project focuses on molecular mechanisms underlying the motility and distribution of plant peroxisomes and mitochondria, multifunctional and metabolically linked organelles essential for energy metabolism and plant viability. An exploratory effort detected directional transport of peroxisomes along actin filaments and discovered candidate proteins functioning at the interface between peroxisomes/mitochondria and the cytoskeleton for organellar motility and distribution in Arabidopsis thaliana. It is hypothesized that the active long-distance movement of peroxisomes/mitochondria along actin filaments is regulated by organelle-specific receptor/adaptor proteins and GTPases, which recruit the actin-associated Myosin XI motors that energize the motility. The project includes three aims: (1) Determining the role of the actin-binding protein Peroxisomal and Mitochondrial Division 1 (PMD1) in mediating the tethering of peroxisomes/mitochondria to the actin filaments; (2) Dissecting the adaptor complex that recruits Myosin XI to the peroxisome by testing the roles of TONSOKU-associated protein 1 (TSA1), the RABE1c GTPase, and the peroxin PEX5; and (3) Dissecting the adaptor complex that recruits Myosin XI to mitochondria by testing the functions of Cardiomyopathy-Associated Protein (CMYA) and the MIRO1 GTPase. Protein immuno-affinity purification, proteomics, live-cell imaging, genetics and physiological phenotyping will be employed to untangle interactions between peroxisomes/mitochondria and the actin cytoskeleton that regulate organelle motility and advance the understanding of the impact of organelle motility on plant fitness. In addition, the project will train both graduate and undergraduate students in modern biological and computational techniques at both universities. Hands-on research experience will be provided to first-year undergraduate students in the classroom with the goal of retaining them in science majors. Discovery-based summer trainings will be provided to undergraduates in molecular biology, genetics, cell biology, physiology, and computational biology in order to prepare them for a scientific career or advanced training after graduation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.