Characterization of beta-tubulin 4 regulated by gibberellins in rice leaf sheath

Tubulins are basic components of microtubules and are encoded by a multigene family in eukaryotes. The expression of OsTUB4, one of eight beta-tubulin isotypes identified in the rice genome, was characterized. OsTUB4 was expressed in root primodia and the shoot apical meristem in basal parts of the leaf sheath in rice seedlings. OsTUB4 transcript abundance in leaf sheath increased by treatment with gibberellic acid (GA(3)) in a dose- and time-dependent manner. OsTUB4 transcript levels in gibberellin (GA)-deficient mutants were less than those of wild type rice. An OsTUB4 promoter::GUS assay also confirmed the responsiveness of OsTUB4 to exogenous GA(3), suggesting that OsTUB4 expression was regulated by GA and may be involved in GA-regulated leaf sheath growth. In addition, OsTUB4 could interact with different specific proteins in vitro as assayed by a yeast two-hybrid system, indicating that OsTUB4 may have diverse functions through interaction with different proteins.