Response of transgenic Arabidopsis expressing maize C 4 photosynthetic enzyme genes to high light.

This study assessed the responses of wild-type (WT) and transgenic Arabidopsis expressing seven combinations of maize ( Zea mays ) genes phosphoenolpyruvate carboxylase ( pepc ), pyruvate phosphate dikinase ( ppdk ), and NADP-malic enzyme ( nadp-me ) to high light. Our results showed that the net CO ₂ assimilation rate ( P _n ) and shoot dry weight of four of the transgenic Arabidopsis genotypes were significantly different from those of WT under high-light treatment, being in the order of Zmpepc+Zmppdk+Zmnadp-me (PC-K-M) > Zmpepc+Zmppdk (PC-K) > Zmpepc (PC), Zmpepc+Zmnadp-me (PC-M) > WT. The other genotypes did not differ from WT. This indicated that Zmpepc was essential for maintaining high photosynthetic performance under high light, Zmppdk had a positive synergistic effect on Zmpepc , and the combination of all three genes had the greatest synergistic effect. These four genotypes also maintained higher photosystem II (PSII) activity (K-phase, J-phase, RC/CSm), electron transfer capacity (J-phase), and photochemical efficiency (TRo/ABS), and accumulated less reactive oxygen species (O ₂ · ^- , H ₂ O ₂ ) and suffered less damage to the membrane system (MDA) than WT under high light. Collectively, PC, PC-K, PC-M, and PC-K-M used most of the absorbed energy for CO ₂ assimilation through a significantly higher P _n , which reduced the generation of excess electrons in the photosynthetic apparatus, thereby reducing damage to the membrane system and PSII. This ultimately resulted in improved high-light tolerance. P _n was the main reason for the significant difference in the high-light tolerance of the four genotypes. Joint expression of the three maize genes may be of great value in the genetic improvement of high-light tolerance in C ₃ crops.