B AMOR terminal disaccharide. Results of structure activity AMOR is bio-active, female-derived arabinogalactan sugar chain, which activates male pollen tubes in plant fertilization1). In a flowering plant Torenia (Figure 1A), pollen tubes become competent by receiving AMOR that is derived from ovules (unfertilized seed tissues), to be attracted by LURE attractant peptides2). LURE attractant peptides are specifically secreted from two egg-accompanied cells, synergid cells, in ovules, but AMOR is derived from egg-surrounding ovule tissues consist of many female cells. Structure-activity relationship study Figure 1. Torenia and bio-active AMOR terminal disaccharide structureby synthetic chemistry revealed that a very specific terminal disaccharide structure, 4-Me-GlcA-β-(1→6)-Gal (Figure 1B), was responsible for AMOR activity3). However, action mechanism of AMOR remains largely unknown. AMOR function in Arabidopsis, a model plant species, remains also unknown. The purpose of this study was to tackle with these issues by combination of synthetic chemistry and physiological/genetic studies. In this study, we tried to examined phenotypes of mutants defective in AMOR (methyl-glucuronosyl galactose) synthesis pathway in Arabidopsis and Torenia. We also tried to develop derivatives of AMOR by adding a crosslinker to develop an AMOR monoclonal antibody and to investigate the action mechanism of AMOR in plants.Arabinogalactan sugar chain is bio-synthesized as a part of arabinogalactan proteins (AGPs). We performed the analysis of glucuronosyltransferase mutants, which are considered to be mutants of the AMOR biosynthetic pathway in Arabidopsis. We summarized the expression patterns of 151 genes encoding arabinogalactan proteins (AGPs) in Arabidopsis and reported them with an overview of current AGP research and methods in plant reproduction5). For glucuronosyltransferase mutants, we mainly used glcat14a-/- b-/- double mutants and glcat14a-/- b-/- c-/- triple mutants. Phenotypes observed during reproduction included reduced pollen tube elongation, abnormal pollen tube morphology, and reduced pollen tube attraction. Western blotting analysis using LM2, a monoclonal antibody that recognizes glucuronidation, Exploring the AMOR biosynthetic pathwayFigure 2 shows AMOR assay of Torenia, whereby competency of pollen tubes is assessed; competent pollen tubes are attracted to a micromanipulated female tissue secreting LURE peptides. By AMOR assay, we could examine AMOR activity of fractions or compounds added to the medium. Activation of pollen tubes by AMOR is conceptually similar to the capacitaion of animal sperms in the female tract4). A A flowering plant, Torenia fournieri, in which AMOR was discovered.relationship study are indicated.63Action mechanism of bio-active sugar chain AMORTetsuya HigashiyamaInstitute of Transformative Bio-Molecules, Nagoya University(Current Institution: Graduate School of Science, The University of Tokyo)
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