Involvement of gibberellic acid and auxin in the regulation of mycorrhizal symbiosis in Bletilla striata (Orchidaceae)
C. MIURA (1), T. Yamamoto (2), M. Yamato (3), S. Nagata (2), Y. Otani (2), H. Asao (4), M. Matsumoto (4), T. Yagame (5), S. Shigenobu (4) (1) Tottori University, Japan; (2) Tottori University, Japan; (3) Chiba University, Japan; (4) National Institute for Basic Biology, Japan; (5) Tsukuba Botanical Garden, National Museum of Nature and Science, Japan

All orchid species rely on mycorrhizal fungi, at least in their early seedling stage, for gaining nutrients. To clarify the mechanism of orchid mycorrhizal (OM) symbiosis, we performed the transcriptome analysis of symbiotic germinated B. striata with its symbiont Tulasnella sp. The symbiotic-germinated protocorms were sampled at 1, 2, and 3 weeks after germination. The expression of symbiosis-related genes and phytohormone-related genes was significantly altered during the experiment. In particular, genes encoding auxin-responsive and -repressed proteins were down- and up-regulated, respectively, in the late stage of symbiosis. In the same stage, gibberellic acid (GA) biosynthesis genes were up-regulated. Because auxin and GA were previously reported to cause positive and negative effects on arbuscular mycorrhizal (AM) symbiosis, respectively, the comparison of total numbers of symbiotic cells among orchid-fungal co-cultures with or without auxin or GA was conducted. The number of symbiotic cells was increased by auxin treatment, and decreased by GA treatment. These results imply that a common mechanism may underlie, at least in part, between OM symbiosis and AM symbiosis.    

Abstract Number: P2-38
Session Type: Poster