Differential expression of three genes for different beta-tubulin isotypes during the initial culture of Zinnia mesophyll cells that divide and differentiate into tracheary elements.

Abstract

Complementary DNA clones for three different beta-tubulin isotypes (ZeTubB1, ZeTubB2 and ZeTubB3) were isolated from a cDNA library generated from RNA of cultured mesophyll cells of Zinnia elegans that were differentiating into tracheary elements and/or dividing. Sequence analysis revealed that the proteins encoded by ZeTubB1 and ZeTubB3 and that encoded by ZeTubB2 were each homologous to two of three groups of beta-tubulin isotypes in Arabidopsis. RNA gel blot analysis of the expression of the ZeTubB transcripts indicated that transcripts that corresponded to each clone were differently expressed during culture of Zinnia mesophyll cells. In particular, the level of expression of ZeTubB1 and ZeTubB3 transcripts increased rapidly prior to cell division and secondary wall formation, and such expression was promoted by combinations of auxin and cytokinin that induced tracheary element differentiation as well as cell division. Results of an in situ hybridization experiment with an antisense RNA probe derived from ZeTubB1 cDNA suggested the preferential expression of ZeTubB transcripts in differentiating xylem cells, as well as in the ground meristem and the procambium, of Zinnia seedlings.