Suppression of endogenous α and β tubulin synthesis in transgenic maize calli overexpressing α and β tubulins

Abstract

Maize Black Mexican Sweetcorn cells have been transformed with constructs containing α and β tubulin coding sequences either singly or together. It is shown that recovery of stable maize transformants is dependent on the co-expression of transfected α and β tubulin in the same lines, indicating that plant cells cannot tolerate an imbalance in the ratio of α tubulin to β tubulin within the cytoplasm. The co-expression of transfected α and β tubulin in maize cells results in an increase in the overall tubulin content (approximately threefold). The transfected α and β tubulins are incorporated into cortical, spindle and phragmoplast microtubule arrays indicating that they are functional. Furthermore, the co-expression of the transfected α and β tubulins results in the suppression of endogenous α and β tubulin synthesis. This suppression increases 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 implications for the post-transcriptional and post-translational regulation of tubulin synthesis in plant cells are discussed.