MEMBERS OF THE ARABIDOPSIS ACTIN GENE FAMILY ARE WIDELY DISPERSED IN THE GENOME

Plant genomes are subjected to a variety of DNA turnover mechanisms th at are thought to result in rapid expansion and presumable contraction of gene copy number. The evolutionary history of the 10 actin genes i n Arabidopsis thaliana is well characterized and can be traced to the origin of vascular plant genomes. Knowledge about the genomic position of each actin gene may be the key to tracing landmark genomic duplica tion events that define plant families or genera and facilitate furthe r mutant isolation. All 10 actin genes were mapped by following the se gregation of cleaved amplified polymorphisms between two ecotypes and identifying actin gene locations among yeast artificial chromosomes. T he Arabidopsis actin genes are widely dispersed on four different chro mosomes (1, 2, 3, and 5). Even the members of three closely related an d recently duplicated pairs of actin genes are unlinked. Several other cytoskeletal genes (profilins, tubulins) that might have evolved in c oncert with actins were also mapped, but showed few patterns consisten t with that, evolutionary history. Thus, the events that gave rise to the actin gene family have been obscured either by the duplication of very small genic fragments or by extensive rearrangement of the genome .