Changes in the transcript levels of microtubule-associated protein MAP65-1 during reorientation of cortical microtubules in azuki bean epicotyls

Abstract

The relation between orientation of cortical microtubules and the transcript levels of a 65 kDa microtubule-associated protein (VaMAP65-1) was investigated along epicotyls of azuki bean (Vigna angularis) seedlings. In addition, the effects of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, and hypergravity, a gravitational force exceeding 1g, on the relation were examined. The percentage of cells with longitudinal microtubule increased, whereas that with transverse microtubules decreased from the apical to the basal regions of epicotyls. The transcript levels of VaMAP65-1 decreased toward the basal region. ACC induced reorientation of cortical microtubules from transverse to longitudinal directions and down-regulation of VaMAP65-1 expression. Hypergravity also induced reorientation of cortical microtubules and down-regulation of the expression. Strong correlations were observed between the percentage of cells with longitudinal or transverse microtubules and the transcript levels of VaMAP65-1. These results suggest that down-regulation of VaMAP65-1 expression is at least partly involved in the regulation of the orientation of cortical microtubules in azuki bean epicotyls.