title: Overexpression of rubisco activase decreases the photosynthetic CO2 assimilation rate by reducing rubisco content in rice leaves.
abstract: The effects of overexpression of Rubisco activase on photosynthesis were studied in transgenic rice expressing barley or maize Rubisco activase. Immunoblot and SDS-PAGE analyses showed that transgenic lines from both gene constructs expressed the foreign Rubisco activase at high levels. The activation state of Rubisco in transgenic lines was slightly higher than that in non-transgenic plants (NT). In addition, light activation of Rubisco was significantly more rapid in transgenic lines compared with NT. These findings indicate that the overexpression of Rubisco activase can enhance Rubisco activation. However, despite enhanced activation of Rubisco in these transgenic plants, the CO(2) assimilation rate at ambient CO(2) conditions was decreased. This decrease in CO(2) assimilation rate was observed in both young developing and mature leaves independent of nitrogen nutrition. The contents of nitrogen and Chl did not differ significantly between transformants and NT; however, Rubisco content was substantially decreased in transgenic lines. There was no evidence for reduced transcription of RbcS or RbcL in these transgenic lines; in fact, transcript levels were marginally increased compared with NT. These results indicate that the overexpression of Rubisco activase leads to a decrease in Rubisco content, possibly due to post-transcriptional mechanisms.
authors.affiliation: Laboratory of Crop Science, Graduate School of Agricultural Science, Kobe University, Kobe, 657-8501 Japan. fukayama@people.kobe-u.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fukayama
authors.forename: Chiaki
authors.initials: C
authors.lastname: Ueguchi
authors.forename: Kaoru
authors.initials: K
authors.lastname: Nishikawa
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Katoh
authors.forename: Chie
authors.initials: C
authors.lastname: Ishikawa
authors.forename: Chisato
authors.initials: C
authors.lastname: Masumoto
authors.forename: Tomoko
authors.initials: T
authors.lastname: Hatanaka
authors.forename: Shuji
authors.initials: S
authors.lastname: Misoo
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008027:Light; D009584:Nitrogen / Q000378:metabolism; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D010788:Photosynthesis; D018515:Plant Leaves / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015854:Up-Regulation
chemical_list: D010940:Plant Proteins; C054765:rca protein, plant; D002734:Chlorophyll; D002245:Carbon Dioxide; C101625:RbcL protein, plastid; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen