Chloroplast and mitochondria interplay in Physcomitrium patens

Chloroplasts and mitochondria are the key bioenergetic organelles in plant cells. Metabolic coordination and retrograde communication between them are essential for maintaining plant cellular homeostasis under various environmental conditions. In the model moss Physcomitrium patens, we recently demonstrated that AMBRA1 (Activating Molecule in Beclin-1 Regulated Autophagy 1), protein that is involved in regulation of autophagy, mitophagy, and cell proliferation in animal cells, is involved in light perception. This project aims to better characterize the role of AMBRA1 in light signaling and test for the first time its putative role in mitophagy in P. patens. To evaluate the involvement of AMBRA1 in mitochondrial physiology, we generated transgenic P. patens lines expressing the mitochondrial outer membrane marker HA-EGFP-PpTOM5 in both wild-type (WT) and ambra1 knockout (KO) backgrounds, validating its localization via confocal microscopy. Phenotypic characterization of WT, AMBRA1 overexpressing lines (OE) and ambra1 KO protonema filaments, specifically measuring cell elongation and subapical branching patterns of chloronema and caulonema cells, was conducted under various light conditions and via vertical dark-spot test assays. Preliminary morphometric data show distinct alterations in cell elongation and filament branching within the subapical zones of ambra1 KO and OE lines, indicating a major role of AMBRA1 in cell development.