APE1 localizes to chloroplast stromules and interacts with ATI1 in Arabidopsis.

Chloroplast stromules are dynamic tubular extensions implicated in inter-organelle communication and stress responses in plants. However, the molecular mechanisms underlying stromule-mediated processes remain largely unexplored. In this study, we investigated the localization and function of ACCLIMATION OF PHOTOSYNTHESIS TO ENVIRONMENT1 (APE1) and its interaction with the autophagy-related protein ATG8-INTERACTING PROTEIN1 (ATI1) in Arabidopsis thaliana. Expression analysis revealed that APE1 is predominantly expressed in rosette leaves. Using yeast two-hybrid and luciferase complementation assays, we confirmed a direct interaction between APE1 and ATI1. Confocal microscopy demonstrated that APE1 localizes both within chloroplasts and stromules, co-localizing with stromule markers, while sub-organelle fractionation indicated APE1 enrichment in the thylakoid and inner envelope membranes. Our findings suggest that APE1, through its interaction with ATI1, may play a crucial role in stromule-mediated signaling and the selective autophagic degradation of chloroplast proteins during stress acclimation. This work provides new insights into the functional dynamics of stromules and highlights the importance of the APE1-ATI1 interaction in chloroplast-nucleus communication under environmental stress.