Probable membrane-remodeling GTPase that plays a unique role in the in the determination of thylakoid and chloroplast morphology and regulates organization of the thylakoid network. Not involved in the determination of mitochondrial morphology or ultrastructure. Localizes in a punctate pattern in chloroplasts. Pale green leaves phenotype and delayed flowering (PubMed:16617119). Decreased number of chloroplasts and heterogeneity in size in mature mesophyll cells (PubMed:16617119, PubMed:23963675). Abnormalities in chloroplast and thylakoid morphology, including disorganized grana stacks and alterations in the relative proportions of grana and stroma thylakoids (PubMed:16617119). Lesion mimic phenotype with activation of defense response markers in the ecotype Landsberg erecta (PubMed:23963675). Belongs to the TRAFAC class dynamin-like GTPase superfamily. Dynamin/Fzo/YdjA family. Mitofusin subfamily.