Zhongbang Song

Overexpression of an HPS/PHI fusion enzyme from Mycobacterium gastri in chloroplasts of geranium enhances its ability to assimilate and phytoremediate formaldehyde.

Abstract3-Hexulose-6-phosphate synthase (HPS) and 6-phosphate-3-hexuloisomerase (PHI) are two key enzymes in the formaldehyde (HCHO) assimilation pathway in methylotrophs. The HPS/PHI fusion protein, encoded by the chimeric gene of hps and phi from Mycobacterium gastri MB19, possesses both HPS and PHI activities in an Escherichia coli transformant. Overexpression of the fusion protein in chloroplasts of geranium (Pelargonium sp. Frensham) created a photosynthetic HCHO assimilation pathway according to 13C-NMR analysis. The transgenic plants exhibited an enhanced ability in HCHO-uptake and [14C]HCHO-assimilation. Moreover, the transgenic plants showed greater HCHO-resistance and stronger capacity in purification of the HCHO-polluted air. Therefore, the use of the single chimeric gene may not only greatly simplify the transformation procedure but also improve the efficiency of phytoremediating HCHO in ornamental plants.

C1 metabolism and the Calvin cycle function simultaneously and independently during HCHO metabolism and detoxification in Arabidopsis thaliana treated with HCHO solutions

Formaldehyde (HCHO) is suggested to be detoxified through one-carbon (C1) metabolism or assimilated by the Calvin cycle in plants. To further understand the function of the Calvin cycle and C1 metabolism in HCHO metabolism in plants, HCHO elimination and metabolism by Arabidopsis thaliana in HCHO solutions was investigated in this study. Results verified that Arabidopsis could completely eliminate aqueous HCHO from the HCHO solutions. Carbon-13 nuclear magnetic resonance ((13)C-NMR) analysis showed that H(13)CHO absorbed by Arabidopsis was first oxidized to H(13)COOH. Subsequently, a clear increase in [U-(13)C]Gluc peaks accompanied by a strong enhancement in peaks of [2-(13)C]Ser and [3-(13)C]Ser appeared in Arabidopsis. Pretreatment with cyclosporin A or L-carnitine, which might inhibit the transport of (13)C-enriched compounds into chloroplasts and mitochondria, caused a remarkable decline in yields of both [U-(13)C]Gluc and [3-(13)C]Ser in H(13)CHO-treated Arabidopsis. These results suggested that both the Calvin cycle and the C1 metabolism functioned simultaneously during HCHO detoxification. Moreover, both functioned more quickly under high H(13)CHO stress than low H(13)CHO stress. When a photorespiration mutant was treated in 6 mm H(13)CHO solution, formation of [U-(13)C]Gluc and [2-(13)C]Ser was completely inhibited, but generation of [3-(13)C]Ser was not significantly affected. This evidence suggested that the Calvin cycle and C1 metabolism functioned independently in Arabidopsis during HCHO metabolism.

Erratum to: Physiological and transcriptional analysis of the effects of formaldehyde exposure on Arabidopsis thaliana

Formaldehyde (HCHO) is highly toxic to all living organisms. In this study, the toxic effects of HCHO exposure on Arabidopsis thaliana were analyzed at the physiological and transcriptional levels. Exposure to 2 mM HCHO led to a significant decrease in plant growth and a massive increase in anthocyanin content. A remarkable increase in H2O2 content and elevation in the levels of protein carbonyl and DNA–protein crosslinks were detected in Arabidopsis plants exposed to 2 mM HCHO for a period of 17 h. In contrast, the malondialdehyde content decreased during this period. These results suggested that HCHO stress caused significant oxidative damage to proteins but not membrane lipids during this period. The Affymetrix ATH1 Genome Array was used to evaluate changes in the global gene expression in Arabidopsis plants exposed to 2 mM HCHO over the 17-h period. A total of 620 transcripts were shown to be regulated significantly (at least twofold). The number of down-regulated genes (467) was approximately threefold greater than the number of up-regulated genes (154). Down-regulation in a large number of genes encoding cell surface receptors, cell wall proteins, enzymes related to toxin metabolism, peroxidase, disease resistance protein, multidrug and toxin extrusion and ATP-binding cassette transporters might be an important part of the toxic effects of HCHO exposure on Arabidopsis at the transcriptional level. Up-regulation in many genes encoding heat shock proteins was suggested to be an important protective mechanism for Arabidopsis plants in response to the oxidative damage of proteins. Verification of microarray data by reverse transcription polymerase chain reaction analysis identified typical HCHO-induced and -repressed genes.