Suppression of endogenous alpha and beta tubulin synthesis in transgenic maize calli overexpressing alpha and beta tubulins

Maize Black Mexican Sweetcorn cells have been transformed with constructs c ontaining alpha and beta tubulin coding sequences either singly or together . it is shown that recovery of stable maize transformants is dependent on t he co-expression of transfected alpha and beta tubulin in the same tines, i ndicating that plant cells cannot tolerate an imbalance in the ratio of alp ha tubulin to beta tubulin within the cytoplasm. The co-expression of trans fected alpha and beta tubulin in maize cells results in an increase in the overall tubulin content (approximately threefold). The transfected alpha an d beta tubulins are incorporated into cortical, spindle and phragmoplast mi crotubule arrays indicating that they are functional. Furthermore, the co-e xpression of the transfected alpha and beta tubulins results in the suppres sion of endogenous alpha and beta tubulin synthesis. This suppression incre ases both with the strength of the promoter in the constructs and with the number of copies of the transgenes inserted into the maize genome. The impl ications for the post-transcriptional and post-translational regulation of tubulin synthesis in plant cells are discussed.