RESUMEN
Biotin is an essential cofactor for a variety of carboxylase and decarboxylase reactions and is involved in diverse metabolic pathways of all organisms. In the present study we tested the hypothesis that controlling biotin availability by the expression of Streptomyces avidinii streptavidin, would impede plant development. Transient expression of streptavidin fused to plant signal peptide, bacterial signal peptide or both, in tomato (Lycopersicon esculentum cv. VF36) plants resulted in various levels of tissue impairment, exhibited as lesion development on 1-week-old tomato seedlings. The least toxic construct was introduced to tomato (stable transformation) under the constitutive CaMV 35S promoter, and lesions appeared on stems, flower morphologies were modified and numbers and sizes of fruits were altered. Furthermore, tissue-specific expression of the streptavidin, by means of the beta-phaseolin or TobRB7 promoters, resulted in localised effects, i.e., impaired seed formation or seedless fruits, respectively, with no alteration in the morphology of the other plant organs. External application of biotin on streptavidin-expressing tomato plants prevented the degeneration symptoms and facilitated normal plant development. It can be concluded that expression of streptavidin in the plant cell can lead to local and temporal deficiencies in biotin availability, impairing developmental processes while biotin application restores plant growth cycle.