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Physiological and photosynthetic characteristics of indica Hang2 expressing the sugarcane PEPC gene.

ABSTRACT: Phosphoenolpyruvate carboxylase (PEPC) is known to play a key role in the initial fixation of CO2 in C4 photosynthesis. The PEPC gene from sugarcane (a C4 plant) was introduced into indica rice (Hang2), a process mediated by Agrobacterium tumefaciens. Integration patterns and copy numbers of the gene was confirmed by DNA blot analysis. RT-PCR and western blotting results showed that the PEPC gene was expressed at both the mRNA and protein levels in the transgenic lines. Real-time PCR results indicated that expression of the sugarcane PEPC gene occurred mostly in green tissues and changed under high temperature and drought stress. All transgenic lines showed higher PEPC enzyme activities compared to the untransformed controls, with the highest activity (11.1 times higher than the controls) being observed in the transgenic line, T34. The transgenic lines also exhibited higher photosynthetic rates. The highest photosynthetic rate was observed in the transgenic line, T54 (22.3 μmol m(-2) s(-1); 24.6 % higher than that in non-transgenic plants) under high-temperature conditions. Furthermore, the filled grain and total grain numbers for transgenic lines were higher than those for non-transgenic plants, but the grain filling (%) and 1,000-grain weights of all transgenic lines remained unchanged. We concluded that over-expression of the PEPC gene from sugarcane in indica rice (Hang2) resulted in higher PEPC enzyme activities and higher photosynthesis rates under high-temperature conditions.

SUBMITTER: Lian L

PROVIDER: S-EPMC3968443 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND AND AIMS: In crops other than sugarcane there is good evidence that the size and activity of carbon sinks influence source activity via sugar-related regulation of the enzymes of photosynthesis, an effect that is partly mediated through coarse regulation of gene expression. METHODS: In the current study, leaf shading treatments were used to perturb the source-sink balance in 12-month-old Saccharum spp. hybrid 'N19' (N19) by restricting source activity to a single mature leaf. Changes in leaf photosynthetic gas exchange variables and leaf and culm sugar concentrations were subsequently measured over a 14 d period. In addition, the changes in leaf gene response to the source-sink perturbation were measured by reverse northern hybridization analysis of an array of 128 expressed sequence tags (ESTs) related to photosynthetic and carbohydrate metabolism. KEY RESULTS: Sucrose concentrations in immature culm tissue declined significantly over the duration of the shading treatment, while a 57 and 88% increase in the assimilation rate (A) and electron transport rate (ETR), respectively, was observed in the source leaf. Several genes (27) in the leaf displayed a >2-fold change in expression level, including the upregulation of several genes associated with C(4) photosynthesis, mitochondrial metabolism and sugar transport. Changes in gene expression levels of several genes, including Rubisco (EC 4.1.1.39) and hexokinase (HXK; EC 2.7.1.1), correlated with changes in photosynthesis and tissue sugar concentrations that occurred subsequent to the source-sink perturbation. CONCLUSIONS: These results are consistent with the notion that sink demand may limit source activity through a kinase-mediated sugar signalling mechanism that correlates to a decrease in source hexose concentrations, which, in turn, correlate with increased expression of genes involved in photosynthesis and metabolite transport. The signal feedback system reporting sink sufficiency and regulating source activity may be a potentially valuable target for future genetic manipulation to increase sugarcane sucrose yield.

Project description:BackgroundPhosphoenolpyruvate carboxylase (PEPC) plays an important role in the primary metabolism of higher plants. Several studies have revealed the critical importance of PEPC in the interaction of carbon and nitrogen metabolism. However, the function mechanism of PEPC in nitrogen metabolism is unclear and needs further investigation.ResultsThis study indicates that transgenic rice expressing the sugarcane C4-PEPC gene displayed shorter primary roots and fewer crown roots at the seedling stage. However, total nitrogen content was significantly higher in transgenic rice than in wild type (WT) plants. Proteomic analysis revealed that there were more differentially expressed proteins (DEPs) responding to nitrogen changes in transgenic rice. In particular, the most enriched pathway "glutathione (GSH) metabolism", which mainly contains GSH S-transferase (GST), was identified in transgenic rice. The expression of endogenous PEPC, GST and several genes involved in the TCA cycle, glycolysis and nitrogen assimilation changed in transgenic rice. Correspondingly, the activity of enzymes including GST, citrate synthase, 6-phosphofructokinase, pyruvate kinase and ferredoxin-dependent glutamate synthase significantly changed. In addition, the levels of organic acids in the TCA cycle and carbohydrates including sucrose, starch and soluble sugar altered in transgenic rice under different nitrogen source concentrations. GSH that the substrate of GST and its components including glutamic acid, cysteine and glycine accumulated in transgenic rice. Moreover, the levels of phytohormones including indoleacetic acid (IAA), zeatin (ZT) and isopentenyladenosine (2ip) were lower in the roots of transgenic rice under total nutrients. Taken together, the phenotype, physiological and biochemical characteristics of transgenic rice expressing C4-PEPC were different from WT under different nitrogen levels.ConclusionsOur results revealed the possibility that PEPC affects nitrogen metabolism through regulating GST, which provide a new direction and concepts for the further study of the PEPC functional mechanism in nitrogen metabolism.

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Physiological and photosynthetic characteristics of indica Hang2 expressing the sugarcane PEPC gene.

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