THE COX2 LOCUS OF THE PRIMITIVE ANGIOSPERM PLANT ACORUS-CALAMUS - MOLECULAR-STRUCTURE, TRANSCRIPT PROCESSING AND RNA EDITING

Acorus calamus, or sweet flag, is a semiaquatic plant of uncertain tax onomic position. Molecular phylogenetic analysis using plastid rbcL se quences have suggested that Acorus calamus might be the most ancient s urviving representative of the ancestral monocotyledonous plants. In o rder to provide molecular and phylogenetic data for the mitochondrial genetic system of Acorus, we have determined the structure of a mitoch ondrial locus, the cytochrome oxidase subunit II gene cox2. The Acorus cox2 gene harbors an unusually small group II intron, the smallest pl ant mitochondrial intron known to date. The transcript undergoes C-to- U RNA editing at eight sites. One of these sites is likely to play a d ual functional role in both intron splicing and protein function. The 3' end of the mature transcript folds into a characteristic stem-loop structure that is presumably required for mitochondrial mRNA stability . Phylogenetic analysis of the cox2 sequence data, as well as the unus ual intron structure, all support an evolutionarily isolated position for Acorus calamus.