Investigating the chloroplast-to-nucleus signaling that regulates plasmodesmata- mediated intercellular trafficking in plants

Intercellular communication via plasmodesmata (PD) is important for plant growth, development, and defense, yet its regulation remains poorly understood. Chloroplasts communicate information about the environment and the physiological state of the plant cell to the nucleus. Chloroplast-generated signals may change the expression of PD-related nuclear genes to regulate the trafficking of photosynthetic products and metabolites along with other molecules that act non-cell autonomously. We aim to identify the chloroplast retrograde signals that regulate intercellular trafficking via PD. Here, we show that tetrapyrroles, likely heme, regulate some aspects of PD-mediated intercellular trafficking. This regulation is not dependent on light. In addition to revealing the potential role of tetrapyrroles in regulating intercellular trafficking, we also revealed that the glucosinolates, a group of specialized metabolites best known for their roles in antimicrobial defense in select plant families, can act as signals to regulate PD-mediated intercellular communication. In contrast to previous reports, we did not identify any correlation between PD-mediated intercellular trafficking and the level of reactive oxygen species (ROS), the redox status of the chloroplast, or plastoquinone redox status. In a related study, we performed differential gene expression analyses and Gene Ontology (GO) analyses and then created protein-protein-interaction networks using differentially expressed genes (DEGs) encoding proteins. Understanding how tetrapyrroles, and in the broader sense chloroplast-to-nucleus retrograde signaling, control trafficking through PD could enable the engineering of plants to optimize carbon partitioning to various parts of the plant for higher yield or to limit pathogen spread. In toto, the studies presented in this thesis have advanced our understanding of the cellular players that regulate the movement of molecules and signals between plant cells, an indispensable portion of the cell-to-cell communication that the coordinated growth, development and environmental responses that are characteristic of and necessary for multicellularity.