Poster: Vegetative Development

Abs # 423: Analysis of the HD-Zip III homeobox genes ZeHB-10, -11, -12 and -13 in relation to vascular differentiation in Zinnia

Presenter:	Ohashi-Ito, Kyoko , ss17195@mail.ecc.u-tokyo.ac.jp
Authors	Ohashi-Ito, Kyoko  (A)   Demura, Taku  (B)   Fukuda, Hiroo  (A) (B)
Affiliations:	(A): Department of Biological Sciences, Graduate School of Science, University of Tokyo (B): Plant Science Center, RIKEN

We isolated novel four homeobox genes (ZeHB-10, -11, -12 and -13) from Zinnia elegans to elucidate the molecular mechanism underlying vascular system formation. ZeHB-10, -11, -12 and -13 encode for HD-Zip proteins of the class III to which Arabidopsis Athb-8, -9, -14, -15 and IFL1 belong. In situ hybridization analysis demonstrated that the ZeHB-10, -11, -12 and -13 mRNAs accumulated preferentially in vascular regions in 14-day-old plants. Transcripts for the four genes also accumulated in cultured Zinnia cells in a xylogenesis-specific manner. The accumulation of transcripts for ZeHB-10, -11 and -12 in cultured Zinnia cells was suppressed strongly by uniconazole, an inhibitor of brassinosteroid synthesis, and such suppression was reversed by the addition of brassinolide, a biologically active brassinosteroid. Thus endogenous levels of brassinosteroids may regulate the expression of ZeHB-10, -11 and -12. However the accumulation of transcript for ZeHB-13 was not affected by brassinosteroid. The ZeHB-13 transcript was detected earlier than the ZeHB-10, -11 and -12 transcripts during xylem differentiation in a Zinnia cell culture. In situ hybridization analysis showed that ZeHB-13 transcript was more strictly restricted to procambium than the other genes. These results suggest that ZeHB-13 regulates earlier step of xylem differentiation than ZeHB-10, -11 and -12. Now efforts are underway to reveal the relation between vascular system formation and brassinosteroid, and we will discuss the roles of HD-Zip III genes in vascular development.