Trans-activation of the maize transposable element, Ds, in Brassica napus

A two-component transposable element system consisting of a stabilized Activator ( Ac(st)) and a chimeric Dissociation ( Ds) element has been introduced into the genome of Brassica napus. Analyses performed on F2 progeny derived from crosses between Ac(st)- and Ds-bearing parents confirm that Ac transposase catalyzes the somatic excision of the Ds element in both embryonic and non-embryonic tissues of this important crop species. The data further reveal that the vast majority of plants containing both Ac(st) and Ds exhibit Ds excision. However, the level of excision is low and germinal Ds excision events are not observed. We estimate that germinal excision of Ds occurs at a frequency of < 0.2%. RT-PCR analysis of the Ac(st) transcript in somatically active seedlings reveals that introns III and IV are highly misprocessed. The pattern of transcript processing is very similar to that observed in germinally inactive but somatically active Arabidopsis seedlings. We suggest that Ds excision activity in B. napus is highly dependent on the efficiency of Ac(st) transcript processing.