Phosphoenolpyruvate carboxylase (PEPC) is a crucial enzyme that catalyzes an irreversible primary metabolic reaction in plants. Previous studies have used transgenic plants expressing ectopic PEPC forms with diminished feedback inhibition to examine the role of PEPC in carbon and nitrogen metabolism. To date, the in vivo role of PEPC in carbon and nitrogen metabolism has not been analyzed in plants. In this study, we examined the role of PEPC in plants, demonstrating that PPC1 and PPC2 were highly expressed genes encoding PEPC in Arabidopsis (Arabidopsis thaliana) leaves and that PPC1 and PPC2 accounted for approximately 93% of total PEPC activity in the leaves. A double mutant, ppc1/ppc2, was constructed that exhibited a severe growth-arrest phenotype. The ppc1/ppc2 mutant accumulated more starch and sucrose than wild-type plants when seedlings were grown under normal conditions. Physiological and metabolic analysis revealed that decreased PEPC activity in the ppc1/ppc2 mutant greatly reduced the synthesis of malate and citrate and severely suppressed ammonium assimilation. Furthermore, nitrate levels in the ppc1/ppc2 mutant were significantly lower than those in wild-type plants due to the suppression of ammonium assimilation. Interestingly, starch and sucrose accumulation could be prevented and nitrate levels could be maintained by supplying the ppc1/ppc2 mutant with exogenous malate and glutamate, suggesting that low nitrogen status resulted in the alteration of carbon metabolism and prompted the accumulation of starch and sucrose in the ppc1/ppc2 mutant. Our results demonstrate that PEPC in leaves plays a crucial role in modulating the balance of carbon and nitrogen metabolism in Arabidopsis.

Odorant-binding proteins (OBPs) play an important role in insect olfaction by mediating interactions between odorants and odorant receptors. We report for the first time 20 OBP genes in the tsetse fly Glossina morsitans morsitans. qRT-PCR revealed that 8 of these genes were highly transcribed in the antennae. The transcription of these genes in the antennae was significantly lower in males than in females and there was a clear correlation between OBP gene transcription and feeding status. Starvation over 72 h post-blood meal (PBM) did not significantly affect the transcription. However, the transcription in the antennae of 10-week-old flies was much higher than in 3-day-old flies at 48 h PBM and decreased sharply after 72 h starvation, suggesting that the OBP gene expression is affected by the insect’s nutritional status. Sequence comparisons with OBPs of other Dipterans identified several homologs to sex pheromone-binding proteins and OBPs of Drosophila melanogaster.Electronic supplementary materialThe online version of this article (doi:10.1007/s00018-009-0221-1) contains supplementary material, which is available to authorised users.

Proline-rich antimicrobial peptides (PR-AMPs) are a group of cationic host defense peptides that are characterized by a high content of proline residues. Up to now, they have been reported in some insects, vertebrate and invertebrate animals, but are not found in plants. In this study, we performed an in silico screening of antimicrobial peptides, which led to discovery of a Brassica napus gene encoding a novel PR-AMP. This gene encodes a 35-amino acid peptide with 13 proline residues, designated BnPRP1. BnPRP1 has 40.5% identity with a known proline-rich antimicrobial peptide SP-B from the pig. BnPRP1 was artificially synthetized and cloned into the prokaryotic expression vector pET30a/His-EDDIE-GFP. Recombinant BnPRP1 was produced in Escherichia coli and has a predicted molecular mass of 3.8 kDa. Analysis of its activity demonstrated that BnPRP1 exhibited strong antimicrobial activity against Gram-positive bacterium, Gram-negative bacterium, yeast and also had strong antifungal activity against several pathogenic fungi, such as Sclerotinia sclerotiorum, Mucor sp., Magnaporthe oryzae and Botrytis cinerea. Circular dichroism (CD) revealed the main secondary structure of BnPRP1 was the random coil. BnPRP1 gene expression detected by qRT-PCR is responsive to pathogen inoculation. At 48 hours after S. sclerotiorum inoculation, the expression of BnPRP1 increased significantly in the susceptible lines while slight decrease occurred in resistant lines. These suggested that BnPRP1 might play a role in the plant defense response against S. sclerotiorum. BnPRP1 isolated from B. napus was the first PR-AMP member that was characterized in plants, and its homology sequences were found in some other Brassicaceae plants by the genome sequences analysis. Compared with the known PR-AMPs, BnPRP1 has the different primary sequences and antimicrobial activity. Above all, this study gives a chance to cast a new light on further understanding about the AMPs’ mechanism and application.

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