EDITING OF THE CHLOROPLAST NDHB ENCODED TRANSCRIPT SHOWS DIVERGENCE BETWEEN CLOSELY-RELATED MEMBERS OF THE GRASS FAMILY (POACEAE)

The ndhB-encoded transcript from barley chloroplasts deviates from the genomic ndhB sequence by nine C-to-U transitions, which is the maximu m number of editing events for a chloroplast mRNA reported so far. Com parison with ndhB transcripts from other chloroplast species shows tha t six of the nine editing sites observed in barley are structurally an d functionally conserved in maize, rice and tobacco. The remaining thr ee sites, however, show divergent patterns of conservation even within the three members of the grass family. The conservation of two of the se sites in tobacco but not in the closely related graminean species s uggests that divergence of the ndhB editing sites is caused by the los s of preexisting editing sites rather than by gain of new sites.