Expression analyses of β-tubulin isotype genes in rice

Microtubules play important roles in many cellular processes, such as cell division and cell elongation in plants. beta-tubulins, which are the basic components of microtubules, are encoded by multigene family in eukaryotes and their nucleotide sequences are highly conserved in protein coding regions. A homology search within the rice expressed sequence tag database identified at least eight beta-tubulin (OsTUB) isotypes including three novel OsTUB genes. Northern analysis using specific probes to 3'-UTR of OsTUB isotypes showed differential and tissue-specific expression. Seven out of eight OsTUB genes dominantly expressed in leaf sheath, while OsTUB8 was preferentially expressed in anther including mature pollens. The existence of anther-specific P-tubulin suggests its unique role in the formation of microtubules during the anther and pollen development or pollen tube growth. Furthermore, transcripts of OsTUB5, 6 and 7 genes were significantly enhanced by gibberellin but all eight OsTUB genes were repressed by abscisic acid. Our results imply that OsTUB genes are differentially regulated by developmental and hormonal signals and different OsTUB isotypes might play special role in the growth and development of specific organs in rice.