PARENT SESSION
Posters P8B Supermolecular organization of the photosynthetic apparatus. Abstracts (592-611)

Suppression of psbP and psbQ genes in Nicotiana tabacum by RNA interference technique. Yumiko Yamamoto^*,1, Kentaro Ifuku¹, Fumihiko Sato¹, ¹ Graduate School of Biostudies, Kyoto, Japan

ABSTRACT- The extrinsic proteins present in the luminal space of thylakoid membranes play crucial roles in optimizing the water-oxidizing activity in photosystem II (PSII). One of the components, PsbO, is ubiquitous among all oxygen-evolving photosynthetic organisms, while the other extrinsic proteins are different between the species. In higher plants, PsbO, PsbP and PsbQ proteins constitute the major parts, and have been extensively analyzed from biochemical and structural standpoints. However, their physiological functions in vivo have been poorly understood due to the difficulty in gene silencing. In this study, we have succeeded in generating two transgenic tobacco plants, psbPir and psbQir, in which the expression of psbP and psbQ genes unique to green algae and higher plants was selectively suppressed by RNA interference technique. Immunoblot analyses of total proteins from leaves of these two transformants revealed that a lack of PsbQ did not affect the accumulation of the other extrinsic proteins, PsbO and PsbP, and the major subunits of the PSII core complex, whereas a lack of PsbP led to a complete loss of PsbQ. Taking account of the finding obtained by in vitro reconstitution experiments that the binding of PsbO and PsbP to the PSII membranes is a prerequisite for the association of PsbQ in higher plants, the behavior of the extrinsic proteins in psbPir implies that unassembled PsbQ is unstable and rapidly degraded after translation in vivo. The psbQir could not be distinguishable from the wild-type under examined conditions, while the psbPir exhibited distinct phenotypes such as drastic reduction in the growth rate, pale green-colored leaves and hypersensitivity to light. In chlorophyll fluorescence measurements, psbPir displayed a high Fo level and a decreased ratio of Fv/Fm, suggesting that the absence of PsbP impairs the electron transfer in the PSII. Further characterization of the transformants is in progress.

KEY WORDS: PsbP, photosystem II, PsbQ, RNA interference