Plasmodesmata and chloroplasts in integrative defense signaling

University Of Delaware, Newark DE

Investigators

Abstract

One of the most effective ways to stop spreading a contagious disease is self-isolation. However, when self-isolation does not happen at the right timing, the spread of disease could go unruly. This is also true at the cellular level whether it concerns an animal or plant system. Upon a successful recognition of invading pathogen, host cells deploy defense programs to fight off pathogens. This often involves a phenomenon called programmed cell death, which is an effective immune response. However, if a cell or group of cells undergo cell death without appropriately communicating for neighboring cells to survive, it could result in an unwanted death of the whole organism. Therefore, understanding how cells regulate the relay of cell death or health signal is not only critical to advance our knowledge but also to help engineer new ways to boost host immunity. In plants, various immune signals are produced in chloroplasts, and it is known that both chloroplasts and the intercellular bridges called plasmodesmata are vital for plant defense. Through multi-disciplinary research proposed in this project, the research team aims to investigate how infected cells in plants might deliver chloroplastic immune signals to plasmodesmata and communicate with their surrounding cells to differentially relay death and health signals at the right time and right place. These investigations will be performed using state-of-the-art live-cell imaging techniques and genetically encoded fluorescent sensors introduced into mutant plants that are altered in chloroplasts mobility or plasmodesmal function. Upon pathogen infection, plants can elicit the hypersensitive response (HR), triggering programmed cell death (PCD) of the infected cells while preserving the health of the surrounding cells. HR-PCD is a highly effective form of plant immunity that can potentially lead to new solutions for boosting agricultural productivity without relying heavily on biocides. However, it remains unknown how HR-PCD is contained to just those cells within and near the infection sites. Here, the research team proposes to explore the signal relay between the HR-PCD cells and the healthy cells bordering them. Specifically, they will focus on hydrogen peroxide (H2O2), which is a key type of reactive oxygen species (ROS) required for HR-PCD. The team will track how the H2O2 burst from intracellular chloroplasts is delivered to restrict molecular movement through the plasmodesmata connecting cells within the HR-PCD site and healthy cells surrounding it. Major research aims include: 1) Establishing the timeline between H2O2 burst and PD status; 2) Investigating the potential of a localized H2O2 burst at PD; 3) Exploring the modes of PD regulation within and outside HR-PCD cells. The research team envisions delivering, for the first time, a high-resolution, real-time plasmodesmal permeability map displaying how chloroplast-plasmodesmata interactions may occur at the intra- and intercellular levels. 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.