Tubulin intron sequences: multi-functional tools.

Abstract

Control of plant and -tubulin gene expression is a key process involved in modulating the amount of tubulin in response to changes occurring in microtubule organization and dynamics. Accordingly, external signals or drugs that may interfere with microtubule assembly can determine changes in the level of tubulin expression. Regulation can occur at both transcriptional and translational level and can sometime involve peculiar mechanisms of control (Anthony and Hussey 1998; Breviario and Nick, 2000; Ebel et al., 2001). Recently, it was demonstrated that microtubule depolymerization caused by oryzalin, an antimitotic drug, can lead to a strong decrease in the amount of both and -tubulin. This regulation is mainly exerted at the protein level and involves a reduced rate of protein neo-synthesis as well as increased degradation of the unassembled tubulin polypeptides (Giani et al., 2002). On the other hand, studies performed with genomic region of the rice -tubulin isotype 1 have shown that the first intron present within the coding region is important for providing a high level of expression of a GUS reporter gene in meristematic tissues of transgenic rice plants (Jeon et al., 2002). Constructs lacking this intron showed constitutive, but low level of GUS gene expression. Preliminary data obtained on two additional rice -tubulin isotypes (tuba2 and tuba3) seem to confirm those findings (unpublished results). A similar situation can also be observed while analysing the regulatory sequence upstream from the ATG codon that controls the expression of -tubulin isotype 16 (Fig. 1). As shown for -tubulins, the presence of a long intron within the genomic sequence corresponding to the 5#UTR of the gene is capable of increasing the expression of the GUS reporter gene driven by pro 16 promoter in transient assays performed on rice calli derived from the mature * Corresponding author. Tel.: +39-022-369-9441; fax: +39-022-369-9411. E-mail address: diego@ibv.mi.cnr.it (D. Breviario).