Enzyme of the plastid non-mevalonate pathway for isoprenoid biosynthesis that converts 4-diphosphocytidyl-2C-methyl-D-erythritol 2-phosphate into 2C-methyl-D-erythritol 2,4-cyclodiphosphate and CMP (Probable). Is essential for chloroplast development (PubMed:29143298). 4-CDP-2-C-methyl-D-erythritol 2-phosphate = 2-C-methyl-D-erythritol 2,4-cyclic diphosphate + CMP Binds 1 divalent metal cation per subunit. Isoprenoid biosynthesis; isopentenyl diphosphate biosynthesis via DXP pathway; isopentenyl diphosphate from 1-deoxy-D-xylulose 5-phosphate: step 4/6. Homotrimer. Expressed in roots, leaves, stems, leaf sheaths and young panicles. Induced by jasmonate, copper, UV and chitin oligosaccharide elicitor. Belongs to the IspF family. Extended N-terminus. Extended N-terminus. Extended N-terminus.