Rearrangements in the chloroplast genomes of mung bean and pea

Abstract

All the cleavage sites for the restriction endonucleases BstEII, Kpn I, Pst I, Pvu II, Sac I, Sal I, Sma I and Xho I on the circular chloroplast chromosomes from mung bean and pea were mapped. The mung bean chloroplast genome measures 150 kilobase pairs (kb) in length; it includes 2 identical sequences of 23 kb that contain the ribosomal genes and are arranged as an inverted repeat separated by single-copy regions of 21 and 83 kb. The pea chloroplast genome is only 120 kb in size, has only 1 set of ribosomal genes, and does not possess any detectable repeated sequences. The mung bean inverted repeat structure is common to all other nonleguminous higher plant chloroplast genomes studied, whereas the pea structure was found only in the closely related legume Vicia faba. Loss of 1 copy of the inverted repeat sequence apparently has occurred only rarely during the evolution of the Angiosperms, and in the case of the legumes after the divergence of the mung bean line from the pea-Vicia line. Hybridization data indicate that rearrangements that change the linear order of homologous sequences within the chloroplast genome have been frequent during the course of legume evolution.