Increase in expression level of alpha-tubulin gene in Arabidopsis seedlings under hypergravity conditions.

Under hypergravity conditions, elongation growth of plant shoots is suppressed. The analysis of the changes in gene expression by hypergravity treatment in Arabidopsis hypocotyls by the differential display method showed that a gene encoding alpha-tubulin, which is a component of microtubules, was up-regulated by hypergravity. In Arabidopsis six genes encoding alpha-tubulin (TUA1-TUA6) have been identified. In the present study, we examined the dose-response and the time course relations of the changes in the expression of all six alpha-tubulin genes in Arabidopsis hypocotyls grown under hypergravity conditions. The expression levels of all six alpha-tubulin genes, TUA1-TUA6, were increased by increasing gravity, although the extent was variable among genes. The increase in expression of all alpha-tubulin genes was detected within a few hours, when the seedlings grown at 1 g were transferred to 300 g condition. These results suggest that Arabidopsis hypocotyls regulate the expression level of six alpha-tubulin genes promptly in response to gravity stimuli. The increase in the amount of microtubules due to the activation of tubulin gene expression may be involved in the regulation by gravity signal of shoot growth.