Overproduction of PGR5 enhances the electron sink downstream of photosystem I in a C<sub>4</sub> plant, <i>Flaveria bidentis</i>
Youshi Tazoe, Noriko Ishikawa, Toshiharu Shikanai, Keiki Ishiyama, Daisuke Takagi, Amane Makino, Fumihiko Sato, Tsuyoshi Endo
Abstract
SUMMARY C 4 plants can fix CO 2 efficiently using CO 2 ‐concentrating mechanisms (CCMs), but they require additional ATP. To supply the additional ATP, C 4 plants operate at higher rates of cyclic electron transport around photosystem I (PSI), in which electrons are transferred from ferredoxin to plastoquinone. Recently, it has been reported that the NAD(P)H dehydrogenase‐like complex (NDH) accumulated in the thylakoid membrane in leaves of C 4 plants, making it a candidate for the additional synthesis of ATP used in the CCM. In addition, C 4 plants have higher levels of PROTON GRADIENT REGULATION 5 ( PGR5 ) expression, but it has been unknown how PGR5 functions in C 4 photosynthesis. In this study, PGR5 was overexpressed in a C 4 dicot, Flaveria bidentis . In PGR5‐overproducing (OP) lines, PGR5 levels were 2.3‐ to 3.0‐fold greater compared with wild‐type plants. PGR5‐like PHOTOSYNTHETIC PHENOTYPE 1 (PGRL1), which cooperates with PGR5, increased with PGR5. A spectroscopic analysis indicated that in the PGR5‐OP lines, the acceptor side limitation of PSI was reduced in response to a rapid increase in photon flux density. Although it did not affect CO 2 assimilation, the overproduction of PGR5 contributed to an enhanced electron sink downstream of PSI.