Comprehensive identification and analysis of extracellular signaling molecules involved in vascular tissue formation

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1. Isolation and characterization of TDIF: We succeeded in isolating TDIF, which is composed of 12 amino acid residues with two hydroxyproline residues and suppresses tracheary element differentiation. The gene for TDIF belonged to the CLE gene family. 2. Identification of the CLV3 peptide: We examined the activity of various size of CLV3 peptides against the shoot meristem formation, and found that 12 amino acids with 2 hydroxyproline residues are necessary and sufficient to suppress the meristem formation. 3. Various functions of CLE peptides: Twenty six chemically synthesized CLE peptides were tested for activities for various events including tracheary element differentiation and found their specificity and redundancy. 4. Analysis of xylogen homologues: We found 15 genes related to the xylogen genes in Arabidopsis genome and examined their expression pattern. Some of them were expressed preferentially in vascular tissues, but the others were expressed in distinctive tissues, suggesting their distinctive functions. 5. Analysis of procambium-specific genes using a gene trap line: We succeeded in the isolation of several genes that are expressed in preferentially in the procambium. 6. Analysis of the gamma-glutamyl hydrolase (GGH) gene: GGH1 is one of the genes that are expressed preferentially in the procambium. GGH shortens polyglutamate chains of the poly glutamate type of folic acid. The loss-of-function and gain-of-function analyses of GGHI, GGH2 and GGH3 indicated that these genes are involved in meristem formation. Taken together with results from in vitro experiments, we proposed that the poly glutamate type of folic acid plays a critical role in maintenance of stem cells in meristem.