Speaker: Haris Variz, Ph.D. candidate in Aung Lab

Title: "Pathogen effectors, plasmodesmata, and novel vesicular structures in plant immunity"

Abstract: Plasmodesmata (PD) are essential intercellular structures that facilitate the movement of signaling molecules, enabling coordinated growth, development, and immune responses in plants. My dissertation explores novel functional aspects of PD and their modulation by host and microbial factors. I demonstrate that multiple bacterial effectors from Pseudomonas syringae pv. tomato DC3000 are capable of trafficking cell-to-cell through PD in Nicotiana benthamiana. This movement is dependent on the size of the effector. It can also be restricted by PD closure, either through overexpression of PD-LOCATED PROTEIN 5 (PDLP5) or treatment with the pathogen-associated molecular pattern flg22, revealing a PD-dependent pathway exploited by bacterial virulence factors. I further characterize an atypical receptor-like kinase, STRUBBELIG RECEPTOR FAMILY 3 (SRF3), initially identified as a putative functional partner of PDLP5. My findings show that SRF3 resides in the same protein complex as PDLP5 and localizes to PD. Additionally, SRF3 is detected in a newly identified vesicular structure, termed PD Bubbles. These vesicles form under osmotic and cell wall stress conditions, encapsulate extracellular reactive oxygen species (ROS), and are significantly reduced in srf3 mutants, suggesting a role for SRF3 in vesicle biogenesis at the PD-plasma membrane interface. Loss of SRF3 disrupts ROS homeostasis and increases susceptibility to avirulent bacterial infection, implicating SRF3 as a key component in immune regulation. Collaborating with the Whitham lab, I investigate Phakopsora pachyrhizi effector candidate 15 (PpEC15), a conserved aspartic protease. Using confocal microscopy, I demonstrated that PpEC15 localizes to the nucleus and physically interacts with two nuclear-localized soybean proteins: the transcription factor GmNAC83 and the peptide chain release factor GmPCRF. Collectively, this work expands our understanding of plasmodesmata as dynamic regulatory hubs in plant immunity, identifies a novel vesicular structure associated with PD, and highlights the complexity of host-pathogen interactions.