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Abstract Intercellular communication in plants, as in other multicellular organisms, allows cells in tissues to coordinate their responses for development and in response to environmental stimuli. Much of this communication is facilitated by plasmodesmata (PD), consisting of membranes and cytoplasm, that connect adjacent cells to each other. PD have long been viewed as passive conduits for the movement of a variety of metabolites and molecular cargoes, but this perception has been changing over the last two decades or so. Research from the last few years has revealed the importance of PD as signaling hubs and as crucial players in hormone signaling. The adoption of advanced biochemical approaches, molecular tools, and high-resolution imaging modalities has led to several recent breakthroughs in our understanding of the roles of PD, revealing the structural and regulatory complexity of these ‘protoplasmic connecting threads’. We highlight several of these findings that we think well illustrate the current understanding of PD as functioning at the nexus of plant physiology, development, and acclimation to the environment. 

ABSTRACT Environmental stress demands precise coordination among organelles to maintain cellular homeostasis. InArabidopsis, high light (HL) exposure triggers chloroplast‐dependent remodeling of mitochondrial and endoplasmic reticulum (ER) morphology specifically in adaxial and abaxial epidermal cells, but not in mesophyll cells. Live‐cell imaging reveals that HL rapidly suppresses mitochondrial motility, followed by fusion‐driven elongation and ER cisternal expansion. Inhibition of photosynthetic, but not mitochondrial, electron transport abolishes these changes, confirming chloroplast activity as the upstream trigger. Pharmacological analyses show that exogenous H₂O₂induces mitochondrial elongation, whereas calcium chelation blocks both H₂O₂‐ and HL‐induced responses, demonstrating that chloroplast‐derived H₂O₂activates a Ca²⁺flux essential for remodeling. Proteomic and functional studies identify the Ca²⁺‐binding GTPase MIRO1 as a central integrator of this pathway. MIRO1 overexpression mimics HL‐induced morphodynamics, while mutations disrupting its Ca²⁺‐binding or acetylation motifs abolish the response, establishing Ca²⁺‐dependent MIRO1 activity as a prerequisite for remodeling. Together, these findings reveal an epidermis‐specific, light‐responsive network in which chloroplast‐derived H₂O₂initiates Ca²⁺signaling through MIRO1 to coordinate mitochondrial and ER remodeling—a spatially restricted mechanism of organellar communication and stress adaptation at the plant–environment interface.