Tissue-Preferential Expression of a Rice α-Tubulin Gene,OsTubA1, Mediated by the First Intron

The genomic clone encoding an α-tubulin,OsTubA1, has been isolated from rice (Oryza sativa L.). The gene consists of four exons and three introns. RNA-blot analysis showed that the gene is strongly expressed in actively dividing tissues, including root tips, young leaves, and young flowers. Analysis of chimeric fusions between OsTubA1and β-glucuronidase (GUS) revealed that the intron 1 was required for high-level GUS expression in actively dividing tissues, corresponding with normal expression pattern ofOsTubA1. Fusion constructs lacking the intron 1 showed more GUS staining in mature tissues rather than young tissues. When the intron 1 was placed at the distal region from 5′-upstream region or at the 3′-untranslated region, no enhancement of GUS expression was observed. Sequential deletions of the OsTubA1 intron 1 brought about a gradual reduction of GUS activity in calli. These results suggest that tissue-preferential expression of theOsTubA1 gene is mediated by the intron 1 and that it may be involved in a mechanism for an efficient RNA splicing that is position dependent.