Cloning and expression of the pea gene encoding SBP65, a seed-specific biotinylated protein

Besides biotin-dependent carboxylases, which play key roles in basic metabolism, SBP65 (seed biotinylated protein of 65 kDa of apparent molecular mass), an atypical biotinylated protein, has been described in pea plants. This seed-specific protein is devoid of any carboxylase activity, and shares many physiological and molecular features with late embryogenesis-abundant (Lea) proteins. In a first step toward understanding the role of this peculiar protein, we have demonstrated the role of abscisic acid (ABA) and of the osmotic environment on its expression using northern blot analysis from immature embryos cultured in vitro and germinating mature seeds. Moreover, the cloning and characterization of its gene (referred to as sbp gene) allowed us to define various potential cis-acting elements within the promoter region to account for the observed strict seed-specific expression. The results described in this paper are consistent with a model in which ABA regulates, at least in part, expression of this gene. However, unlike most lea genes, ABA regulation of the sbp gene seems to occur in a very restricted fashion, being confined only to particular stages of embryo development. Such a strict spatial and temporal expression pattern is dependent on the osmotic environment of the developing embryos and on tissue-specific factors, presumably preventing biotin depletion in cells requiring this essential cofactor for basic metabolic activity.