Arabidopsis acyl-CoA-binding protein ACBP6 localizes in the phloem and affects jasmonate composition.

Arabidopsis thaliana ACYL-COA-BINDING PROTEIN6 (AtACBP6) encodes a cytosolic 10-kDa AtACBP. It confers freezing tolerance in transgenic Arabidopsis, possibly by its interaction with lipids as indicated by the binding of acyl-CoA esters and phosphatidylcholine to recombinant AtACBP6. Herein, transgenic Arabidopsis transformed with an AtACBP6 promoter-driven ß-glucuronidase (GUS) construct exhibited strong GUS activity in the vascular tissues. Immunoelectron microscopy using anti-AtACBP6 antibodies showed AtACBP6 localization in the phloem especially in the companion cells and sieve elements. Also, the presence of gold grains in the plasmodesmata indicated its potential role in systemic trafficking. The AtACBP6 protein, but not its mRNA, was found in phloem exudate of wild-type Arabidopsis. Fatty acid profiling using gas chromatography-mass spectrometry revealed an increase in the jasmonic acid (JA) precursor, 12-oxo-cis,cis-10,15-phytodienoic acid (cis-OPDA), and a reduction in JA and/or its derivatives in acbp6 phloem exudates in comparison to the wild type. Quantitative real-time PCR showed down-regulation of COMATOSE (CTS) in acbp6 rosettes suggesting that AtACBP6 affects CTS function. AtACBP6 appeared to affect the content of JA and/or its derivatives in the sieve tubes, which is consistent with its role in pathogen-defense and in its wound-inducibility of AtACBP6pro::GUS. Taken together, our results suggest the involvement of AtACBP6 in JA-biosynthesis in Arabidopsis phloem tissues.

Enhanced production of fatty acids and astaxanthin in Aurantiochytrium sp. by the expression of Vitreoscilla hemoglobin.

Dissolved oxygen is a critical factor for heterotrophic cell growth and metabolite production. The aim of this study was to investigate the effects of an oxygen-involved protein on cell growth and fatty acid and astaxanthin production in the biologically important thraustochytrid Aurantiochytrium sp. The hemoglobin of the Vitreoscilla stercoraria (VHb) gene was fused upstream with a zeocin resistance gene (ble) and driven by the Aurantiochytrium tubulin promoter. The expression construct was introduced into two strains of Aurantiochytrium sp. by electroporation. Transgenic Aurantiochytrium sp. strains MP4 and SK4 expressing the heterologous VHb achieved significantly higher maximum biomass than their corresponding controls in microaerobic conditions. Furthermore, the transformants of Aurantiochytrium sp. SK4 produced 44% higher total fatty acid and 9-fold higher astaxanthin contents than the wild type control in aerobic conditions. The present study highlights the biotechnological application of VHb in high-cell density fermentation for enhanced biomass production as well as high-value metabolites.