Introduction

Have you ever seen flower fairies? Probably no(some of you might come across them in your childhood), because they are imaginary creatures existing only in fairy tales. What if we can live with flower fairies? Their lovely powers to make flowers bloom would be profitable for us, including application to agriculture. That’s why we set our project to realize it with Synthetic biology, Flower Fairy E.coli!

Our goal is to produce E.coli which can make flowers bloom as Flower Fairies. To make it possible, we focus on FT protein, the identity of Florigen.
There are four issues on the way to make Flower Fairy E.coli. It is unclear even whether E.coli could produce FT because FT is usually produced in the eukaryotic plant cell. After producted, FT have to go through four walls, inner and outer membranes, a cell wall of the plant cells and a cell membrane of the plant. Even though FT could get inside, no one knows whether FT protein transcribed in E.coli can activate in plant cells.

FT protein can bloom flowers,but can E.coli make it?

FT, or FLOWER　LOCUS　T, is a protein composed of 175 amino acids. In plants, FT protein is produced in leaves and transported to a shoot apex. And then FT works as a transcription factor and activates floral meristem identity genes, thereby making flowers bloom. FT protein can make flowers bloom at low dose. Because FT is normally produced in a eukaryotic cell, we were not sure whether or not E. coli can synthesize, and FT produced by E. coli works successfully in a cell of thale cress (Arabidopsis thaliana). So, confirmation of the functionality of FT is needed.

Useful Secretion System

Secretion

When we determined to make Flower Fairy E.coli, we found that FT protein don’t exit from cytoplasm to surroundings by itself so that we needed to construct a special system for translocate FT protein. In previous iGEM competition, some kinds of parts and devices for protein translocation were already developed. One of the most widely used part is lysis cassette(このパーツのページのリンク). This part causes cell lysis and, as a result, makes E.coli scatter materials it includes. This style is, unfortunately, not suitable for our project because of the possibility of accidental cell-death. Generally speaking, the concentration of E.coli on plant is not high so that it can’t be ignored that the possibility of occurring all cell-death. Once all our Fairies are disappeared, flower wouldn’t bloom.

...fig2 lysis would kill all of Fairies. Flower can't bloom again....

Experiments&Results

We have to go through four steps for purpose of obtaining our goal－Flowering Fairy E.coli－
The four steps are composed of “EXPRESSION”,”SECRETION”, ”PENETRATION”, and ”ACTIVATION”

1.EXPRESSION

Expression

On the first step; EXPRESSION, E.coli produce florigen inside of the cells.
When we got FT gene, we had a difficulty in constructing iGEM parts. The problem is that FT sequence had two cleavage sites of iGEM restriction enzymes. In order to eliminate cleavage sites of iGEM restriction enzymes, we performed Inverse PCR of plasmids with two kinds of primer which have mutation.
As a result, we could get mutated plasmids, which are not cleaved by iGEM restriction enzymes. In this way, we made FT gene available.

Previous to experiment, whether FT gene is expressed correctly in E.coli had arouse criticism in our team. This is because, under natural environment, FT gene is expressed and functions in plant cells, which are eukaryote. However, E.coli is prokaryote, so no one knows that FT protein which E.coli made could function.
We transformed E.coli and made them express our FT gene. In order to confirm the expression of FT protein, we performed western blotting and checked the place of the FT protein band.

2.SECRETION

Secretion

On the second step; SECRETION, E.coli secretes florigen outside the cell.

Even though our E.coli can produce FT protein, a big issue remains: how they can transport proteins to the outside of the cells? To make it possible, we made Tat cassette and kil protein inducer. This cassette makes E.coli carry proteins with torA signal via Tat protein transportation pathway from cytoplasm to periplasm. Periplasm is a space between inner and outer membrane. Kil protein encourages proteins to move from periplasm to surroundings. Our Secretion team made this protein secretion system and visualized and confirmed its function by using GFP.

We need secretion system without cell-death.

In the previous iGEM competition, some kinds of parts and devices for protein translocation were already developed. One of the most widely used parts is [http://partsregistry.org/Part:BBa_K358004 lysis cassette]. This part causes cell lysis and as a result, makes E.coli scatter materials it has. This style is, unfortunately, not suitable for our project because of the possibility of accidental all-death. Generally speaking, the concentration of E.coli on flower is not high, so we can’t ignore the possibility of all cell-death. Once all our Fairies disappear, flowers wouldn’t bloom. In addition, we tried to seek for an ideal secretion system, which is not harmful to both of our fairies and other livings. Finally, we focused on Twin argenine translocation pathway (Tat pathway) of E.coli. It is not pathogenic and carries various kinds of proteins with torA signal(Tat班古い方のレビュー)

What is TAT Secretion pathway?

The Twin Arginate Translocation pathway(TAT) is a secretion system E.coli originally has. This system can carry proteins that have torA signal anino acid sequences at N terminal. TatA, TatB, TatC and TatD compose Tat complex on inner membrane. Tat complex recognizes torA signal peptide and then it transports proteins (with torA) from cytoplasm to periplasm. In addition, proteins that compose TAT pathway cut off the torA signal. Proteins which are secreted by this system don't have tags that obstruct the activation of the protein.

Our Tat cassette and kil inducer

TatABCD composes pathway from cytoplasm to periplasm. Kil makes holes on outer membrane and we expect that protein goes through this holes. Needless to say, function of outer membrane as membrane is essential for E.coli to survive. In other words, overexpression of Kil causes cell death. In this reason, we must find suitable amount of expression.

Detail of Our Secretion System

Our wonderful secretion system is constructed by tatABCD, Kil and another gene. Another gene is PspA (phage-shock protein A) gene. E.coli has it originally and this gene is expressed when their inner membrane is dameged. PspA meintains H+ concentration gradient between periplasm and cytoplasm and membrane potential. Our secretion system makes many holes on inner and outer membranes. In other words, E.coli which has our secretion system is under the membrane stress conditions. But by introducing pspA into our Flower Fairy E.coli, the E.coli come to be able to maintain the vitality, though they have many holes on the membrane.

Construction

Tat secretion cassette with constitutive promoter(BBa_K797004)

This cassette allow E.coli to secrete proteins with torA signal. Wild type Tat protein secretion system is too week so that Kyoto 2012 construct Tat cassette to reinforce the ability of transportation of Tat system. This parts include tatA,B,C protein coding region and pspA (phage shock protein A). Tat A,B,C protein is the main component of Tat complex where proteins with torA signal go through and pspA can encourage protein secretion via Tat system. Kyoto 2012 suggest iGEMers with this new way of secretion and provide them with this cassette regulated by constitutive promoter.

We checked the sequence of tatABCD(BBa_K797000) and the sequence of pspA (BBa_K797001) individually, and then, we made TAT construction composed of constitutive promoter(BBa_J23107), tatABCD (BBa_K797000),pspA(BBa_K797001) and double terminator (BBa_B0015). This TAT secretion cassette is too long device to sequence, so that we performed electrophoresis of this cassette and confirmed the length of our parts.

Considering that the sequences of tatABCD and pspA are correct,and the length of TAT secretion casssette is correct, we declare that this construction of TAT secretion cassette has been completed.

3.PENETRATION

Penetration

On the third step; PENETRATION, florigen is absorbed into plant cells.

To realize flower fairy E. coli, FT secreted by E. coli must be absorbed in plant cells. From early stage, we sought various ways to penetrate FT protein into plants, but each way has serious problems. For example, girdling can be used, we think. But, it is difficult to inject FT protein exactly in sieve tube.

fig.1 image of R9 peptide (powered by winmostar V3.808d, MOPAC2012)

Polyarginine peptide is thought to act on a cell membrane and cause a specific form of endocytosis, that is, macropinocytosis. Macropinocytosis is not caused by an invagination of the cell membrane, but by the growth on the actin mambrane from protrusions into vesicles called macropinosomes, and no receptors are necessary for the process (fig.2). It is reported that plants use CPP to transport biomolecules such as proteins inside the cell, in spite of their cell walls.
Then, we determined to perform penetration by using FT protein with R9 coding region.

fig.2 how R9 peptide function on cell membrane

2. R9 peptide fusion GFP

Pre-experiment

First, we checked the specificity of anti GFP monoclonal antibody.
We characterized the existing GFP generator parts, BBa_I746915.
The parts is consist of T7 promoter 6-his tagged superfolder GFP.
Cells were precultured overnight and diluted into fresh SOC medium. IPTG was added when OD600 was approx. 0.7, then cells were incubated for 4h at 37°C. 100µL of culture was used for SDS-PAGE.

Following figure shows the result of western blotting of [http://partsregistry.org/Part:BBa_I746915 BBa_I746915].
Unfortunately, we used inappropriate molecular marker and could'nt confirm the molecular weights of samples.

Lane1 : IPTG 0mM, sample 10µL
Lane2 : IPTG 1mM, sample 10µL
Lane3 : IPTG 0mM, sample 5µL
Lane4 : IPTG 1mM, sample 5µL
Lane5 : IPTG 0mM, sample 2µL
Lane6 : IPTG 1mM, sample 2µL

After the 4h of IPTG induction, we noticed that E.coli expressing R9::GFP were growing poorly.


Moreover, we couldn't get any bands of R9::GFP, as shown in the following figure.

Lane1 : Molecular marker
Lane2 : GFP([http://partsregistry.org/Part:BBa_I746915 BBa_I746915]) IPTG 0mM, sample 10µL
Lane3 : GFP([http://partsregistry.org/Part:BBa_I746915 BBa_I746915]) IPTG 1mM, sample 10µL
Lane4 : R9::GFP IPTG 0mM, sample 10µL
Lane5 : R9::GFP IPTG 1mM, sample 10µL

3. Separating R9 peptide and GFP

When R9 and GFP were conected, they didn't work normally. By way of experiment, we separated R9::GFP into two segments and soaked plant cells into a sollution of them.

The control on the left was soaked in only GFP, and on the right-hand side the sample was soaked in GFP and R9. These two pictures show the action of R9 peptide. R9 peptide kept GFP in or around plant cells. This figure strongly suggests that R9 peptide works successfully and penetrates cell membrane with GFP.

4. Activation

Activation

Finaly, we verified whether FT normally worked in plant cells. </br> FT protein is derived from plant cells and it is capable of post-translational modification. E.coli cannot do post-translational modification, so FT protein derived from Flower Fairy E.coli may not work normally.

Considering Probably R9 penetrates cell membranes with proteins, so we injectd a sollution of FT and R9 into plant cells derived from Arabidopsis thaliana. FT protein activates various other proteins. We checked the change of activity of them by RT-PCR.

This is the result of RT-PCR. The left is control. It is

4. Verification of FT Function

fig.1 image of R9 peptide (powered by winmostar V3.808d, MOPAC2012)

Polyarginine peptide is thought to act on a cell membrane and cause a specific form of endocytosis, that is, macropinocytosis. Macropinocytosis is not caused by an invagination of the cell membrane, but by the growth on the actin mambrane from protrusions into vesicles called macropinosomes, and no receptors are necessary for the process (fig.2). It is reported that plants use CPP to transport biomolecules such as proteins inside the cell, in spite of their cell walls.

Discussion

Future Works

We noticed only flowering and florigen in this time but there are many many other plant hormones. We made translocation pathway from E.coli into plant cells, so we will be able to introduce plant hormones into plant cells if E.coli can make them. It means we can control plant growth in any stage through genetically engineered E.coli. In the future that is not so far, we will be able to meddle in plants' growth――germinating, elongation, flowering, and fructification. We human will finally accomplish a technology that control plants perfectly.

Moreover, R9 peptide functions not only plant cell. R9 peptide works on animal cell similarly. It means that we found a pathway into any kinds of cells. R9 peptide tag enables us to introduce proteins into any cells, so we will be able to controll all living cells using this technology.

References

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