In this project, our objective is to further increase plant formaldehyde uptake and metabolism ability using synthetic biology methods. We find some genes encoding key enzymes related to formaldehyde metabolic pathways from microorganism. They are 3-hexulose-6-phosphate (HPS), 6-phospho-3-hexuloisomerase (PHI), formaldehyde dehydrogenase (FALDH) and formate-dehydrogenase (FDH). These genes are inserted into plants and will work to promote formaldehyde metabolism. For security reasons, we also add gene AdCP into our project because of its capability to lead to pollen abortion. At the same time, chloroplast transformation is taken into consideration to decrease the probability of gene flow.

HPS-PHI

The ribulose monophosphate (RuMP) pathway is one of the HCHO-fixation pathways found in microorganisms called methylotrophs, which utilize one-carbon compounds as the sole carbon source. The key enzymes of this pathway are 3-hexulose-6-phosphate synthase (HPS), which fixes HCHO to D-ribulose-5-phosphate (Ru5P) to produce D-arabino-3-hexulose 6-phosphate (Hu6P), and 6-phospho-3- hexuloisomerase (PHI), which converts Hu6P to fructose 6-phosphate (F6P).The two key enzymes work in chloroplast both.We will use fusion expression to conduct heterologous expression in tobacco ( Li-mei Chen et al,2010). Here are some datas from the paper.

FALDH

The glutathione-dependent formaldehyde dehydrogenase (FALDH) plays a key role in formaldehyde metabolism (Fig.3). FALDH is identified as an enzyme expressed in the cytoplasm. If we make FALDH over-express in plants, we can enhance plants’ tolerance to HCHO and increase the ability of plants to absorb HCHO. In the process of metabolism of formaldehyde, the formaldehyde may first combined with glutathione (GSH) to form the product of S-hydroxymethyl glutathione (HM-GSH), then FALDH in cytoplasm will catalyzes the formation of a S-formyl glutathione (F-GSH). Next the F-GSH will be hydrolyzed to formate (HCOOH) and GSH by S-formyl glutathione hydrolase (FGH).

FDH

Formate dehydrogenase is a mitochondrial-localized NAD-requiring enzyme while the HCOOH is getting into the mitochondrial，FDH will oxidize the formic acid into CO2, and reduce NAD+ to NADH with a high degree of specificity.In our project, the heterologous expression of FDH from arabidopsis thaliana in tobacco was completed.

Stomatal opening

Stomata are microscopic pores surrounded by two guard cells and play an important role in the uptake of CO2 for photosynthesis. Recent researches revealed that light-induced stomatal opening is mediated by at least three key components: blue light receptor phototropin, plasma membrane H+-ATPase, and plasma membrane inward-rectifying K+ channels. However, Yin Wang, et al (2014) showed that only increasing the amount of H+-ATPase in guard cells had a significant effect on light-induced stomatal opening (Fig. 4). Transgenic Arabidopsis plants by overexpressing H+-ATPase in guard cells exhibited enhanced photosynthesis activity and plant growth. Therefore,in order to strengthen the ability of absorbing formaldehyde, we overexpressed H+-ATPase (AtAHA2) in transgenic tobacco guard cells,resulting in a significant effect on light-induced stomatal opening.

Biosafty

In order to promise biology safety, we use male sterility systems which can be used as a biological safety containment to prevent horizontal transgene flow. Pawan Shukla et al (2014) has used a plant pathogen-induced gene, cysteine protease for inducing male sterility. This gene was identified in the wild peanut, Arachisdiogoi differentially expressed when it was challenged with the late leaf spot pathogen, Phaeoisariopsispersonata.Arachisdiogoi cysteine protease (AdCP) was expressed under the strong tapetum-specific promoter (TA29) and tobacco transformants were generated. Morphological and histological analysis of AdCP transgenic plants showed ablated tapetum and complete pollen abortion.

Vectors

The production of HPS, PHI, and FDH are located in chloroplast, while the production of FALDH are located in cytoplasm. We used chloroplast transit peptides to locate these productions of genes. So we constructed different vectors with and without transit peptide. We hope to compare the ability of metabolizing HCHO of transgenic tobacco between different transgenic lines. We planned to constructed 11 vectors (Fig. 6), including two backbones, six mono-gene expression vectors and three multi-gene expression vectors (Fig. 7). piGEM003, piGEM004 and piGEM005 are individual mono-gene expression vectors with transit peptides, while piGEM006, piGEM006, piGEM008 are individual multi-gene expression vectors without transit peptides. piGEM009 is a multi-gene expression vector without any transit peptides, while piGEM011 is a multi-gene expression vector with three peptides. piGEM010 is a multi-gene expression vector with two transit peptides.

References

Lu, N., J. Pei, Y. Zhao, R. Qi and J. Liu (2012). "Performance of a biological degradation method for indoor formaldehyde removal." Building and Environment 57: 253-258.
Tang, X., Y. Bai, A. Duong, M. T. Smith, L. Li and L. Zhang (2009). "Formaldehyde in China: production, consumption, exposure levels, and health effects." Environ Int 35(8): 1210-1224.
Xu, Z., N. Qin, J. Wang and H. Tong (2010). "Formaldehyde biofiltration as affected by spider plant." Bioresour Technol 101(18): 6930-6934.
Xu, Z., L. Wang and H. Hou (2011). "Formaldehyde removal by potted plant-soil systems." J Hazard Mater 192(1): 314-318.