PARENT SESSION
Posters P7A Mechanisms of water oxidation. Abstracts (347-381)

Functional analysis of the four PsbP members encoded by multigene family in Nicotiana tabacum. Seiko Ishihara^*,1, Yumiko Yamamoto¹, Kentaro Ifuku¹, Fumihiko Sato^{1, 2}, ¹ Grad. Sch. of Biostudies, Kyoto Univ., Kitashirakawa, Sakyo, kyoto, Japan² Fac. of Agri., Kyoto Univ., kitashirakawa, sakyo, Kyoto, Japan

ABSTRACT- PsbP protein is an extrinsic 23-kDa protein in the oxygen-evolving complex of photosystem II. In amphidiploids Nicotiana tabacum, PsbP is nuclear-encoded by a multigene family of four members, which could be divided into two groups by the sequence similarity (group-I: 1A and 5B; group-II: 2AF and 3F). All PsbP members are expressed in N.tabacum and either of the two members in each group is derived from the ancestral parents, N. sylvestris and N. tomentosiformis. There are several reports showing that the gene expressions of the individual PsbP groups were differentially regulated by particular environmental stimuli. However, the difference of the physiological role between PsbP groups has not been clarified. In order to clarify the physiological role of each group, we generated group-specific PsbP-silenced transgenic tobacco plants by RNA interference. Group-specific suppression, which was confirmed by Western analysis in transgenic tobacco (T1 generation), did not affect the growth of the transgenic plants grown under low light conditions. However, group-II-specific PsbP-silenced (2AFs) tobacco leaves showed bleaching under strong illumination, whereas group-I-specific PsbP-silenced (1As) tobacco did not show visible phenotype. Preliminary analyses in T0 and T1 transgenic tobacco using a PAM fluorometer showed significantly higher Fo and the decreased photosynthetic electron transport rate in 2AFs tobacco than in control tobacco, whereas 1As tobacco was indistinguishable from control tobacco. These results corresponded to their phenotypes and suggest the difference in the function or in the level of expression between the two groups. Further characterization of T2 plants is in progress.

KEY WORDS: gene family, PsbP, Nicotiana tabacum, RNA interference