Enhanced Tolerance of Transgenic Rice Plants Over-Expressing Maize C 4 Phosphoenolpyruvate Carboxylase Gene to Low Nitrogen Conditions

摘要

The present study identified and compared transgenic rice overexpressing maize C 4 pepc (PC) with wild-type (WT; Kitaake) in low nitrogen tolerance through a combination of physiological, metabolic and proteomic analysis. The results showed that PC had smaller decreases and higher dry weight and net photosynthetic rate under low nitrogen conditions compared with WT. The increased photosynthetic rate in PC was associated with higher phosphoenolpyruvate carboxylase (PEPC) activity, pepc gene expression, and antioxidant system enhancement. The transgenic type with PC accumulated less starch or soluble sugars than WT under low nitrogen conditions. Metabolic analysis showed elevated PEPC activity in PC increased the synthesis of malate, citrate and 2-oxoglutarate under low nitrogen conditions. This increase also enhanced enzyme activities of the anaplerotic pathway for the tricarboxylic acid cycle and nitrogen assimilation. Furthermore, leaf N level of PC was higher than WT. Using 2-DE, 12 differentially expressed spots were identified between N deficient PC and WT. The proteins involved in photosynthesis, tricarboxylic acid cycle, amino acid biosynthesis, ROS scavenging, and translation expressed in higher concentration in N deficient PC. The increased carbon flow towards nitrogen metabolism could alleviate the inhibition of photosynthesis and had higher N content in PC under low nitrogen conditions, indicating enhanced tolerance of transgenic type PC to low nitrogen compared with WT.