Poster: Intercellular Signaling

Abs # 803: Xylogen, a locally acting intercellular regulator of tracheary element differentiation

Presenter:	Motose, Hiroyasu , motose@biol.s.u-tokyo.ac.jp
Authors	Motose, Hiroyasu  (A)   Sugiyama, Munetaka  (B)   Fukuda, Hiroo  (A) (C)
Affiliations:	(A): Dept. Biol. Sci., Grad. Sch. Sci., Univ. Tokyo (B): Botanical Gardens, Grad. Sch. Sci., Univ. Tokyo (C): Plant Science Center, RIKEN

Tracheary elements (TEs) are differentiated in contact with each other to form a continuous xylem vessel, raising the possibility that some local intercellular communication functions to guide continuous xylem development. We have investigated intercellular communication involved in TE differentiation of zinnia mesophyll cells and revealed that an arabinogalactan protein mediates local intercellular communication promoting (or inducing) TE differentiation. This factor was named as xylogen with reference to its xylogenic activity. A bioassay system to monitor the activity of xylogen was successfully applied to isolate xylogen from the conditioned medium. Xylogen was deglycosylated into a protein backbone, and its N-terminal amino acid sequence was determined. A cDNA cloned on the basis of this sequence information was found to encode a GPI-anchored arabinogalactan protein, which was judged as the protein backbone of xylogen. We designated this cDNA and the corresponding gene as ZeXYP1 (Zinnia elegans xylogen protein 1). Zinnia cultured cells accumulated mRNA for ZeXYP1 in the presence of auxin. In situ hybridization analysis revealed localization of ZeXYP1 transcripts in immature xylem cells. Transgenic BY-2 cells overexpressing ZeXYP1 had the increased activity of xylogen, supporting that ZeXYP1 encodes the protein backbone of xylogen. We will discuss the significance of xylogen in continuous xylem formation.