Difference between revisions of "Part:BBa K4013005"

Revision as of 15:26, 21 October 2021

aro8

This sequence encodes the ARO8 gene from Saccharomyces cerevisiae.

Sequence and Features

Metabolic pathway of IAA

In our experiments, two ways to convert L-tryptophan to Indole-3-acetic acid (IAA) are used (Figure 1). IPA and IAM pathway, respectively. In our experiment, IPA pathway and IAM pathway were used. The IPA pathway is what we finally need to use to produce IAA on cyanobacteria. It needs three different enzymes to turn L-tryptophan into IAA. On the other hand, IAM pathway needs two enzymes to make IAA. This pathway is used by Imperial College London in 2011 (BBa_K515100).

Enzymes of IPA pathway

IPA pathway requires three enzymes to convert L-tryptophan to IAA in three steps. tryptophan aminotransferase (taa1/aro8) transforms tryptophan into indole-3-pyruvic acid, then indolepyruvate decarboxylase (ipdc/kdc) transforms indole-3-pyruvic acid into indole-3-acetaldehyde, which is converted to indole-3-acetic acid through aldehyde dehydrogenase (aldh/puuc). Among them, aro8 and kdc genes come from yeast, while puuc comes from Escherichia coli.

Construction and function test of IPA Pathway circuits

The Ptac promoter, a functional hybrid promoter found in 2009, can be activated by IPTG. The expression can be increased by the increase of IPTG concentration. We referenced the Ptac promoter into the IPA pathway and these parts are transferred into pET28a vector (Figure 2).

In Figure 2, it shows that we had successfully assembled and made a IPA pathway that can be used in E.coli. We transfer the gene into E.coli DH5a ΔtnaA, a strain invented by Liks_China.

Salkowiski test is a test that can measure the concentration of IAA. It needs a reagent to test it. When we add the reagent into our IAA, we can see the color change. The redder the color, the more IAA it contains. We induced bacteria and did Salkowiski test every 24 hours. We did Salkowiski test for induction of 24 hours, 48 hours and 72 hours. Figure 3 shows our results. It can be seen that our IPA pathway has a high yield.

Transfer IPA Pathway to Cyanobacteria

Synechocystis sp. PCC 6803 is a cyanobacteria which is widely used in synthetic biology. We used some native expression elements of PCC 6803 such as plasmids, promoters and terminators. pCB-SC101 (P2.4-101 vector)(BBa_K4013010) is a native plasmid backbone in PCC 6803 which contains spectinomycin resistance. We also used two different promoters for the IPA pathway, Psll1321 (BBa_K4013000) and Pssl0452 (BBa_K4013001). These two native promoters are relatively weak in PCC 6803. We made this choice because excessive IAA would in

By using the Golden Gate Assembly method, the parts are assembled, and we got two IPA pathways that can be used in cyanobacteria (Figure 6).Figure 6 shows that the pathways are constructed successfully. The two pathways are the pathway with p1321 promoter and the pathway with p0452 promoter (Figure 7). We also apply the Salkowiski test on these two pathways.

In Figure 7, we use the data of induce 48 hours. The data shows that the IAA produced by IPA pathway with p0452 is higher than p1321, but not much. This is expected because promoter p0452 is stronger than p1321.

IAA functional test

In order to prove the effect of our IAA, we designed an experiment. IAA is a plant growth hormone. We used the root growth of mung bean to reflect the effect of IAA. We also used MS media, a plant tissue culture medium containing 7g / L agar and 30g / L sucrose. The experiment was divided into three groups. The experimental group used MS medium containing IAA produced by IPA pathway to grow mung beans, while the two control groups were MS medium containing standard IAA ,and MS medium. Soak mung beans in water for 24 hours and wait for them to germinate. We adjusted the IAA concentration in MS medium to 1.5mg/l. Put the soaked mung bean on the culture medium, contact the root with the culture medium, and wait for the mung bean to grow in a light incubator for about a day. The following results are obtained (Figure 8).

In Figure 8, we can see that the mung bean grows naturally in the group with MS medium, and in other two groups which contains IAA, root growth was significantly inhibited. This is because a certain concentration of IAA will inhibit the growth of plant tissue. In the two groups with IAA, the growth of roots is similar, this means that the activity of our IAA is basically consistent with the standard IAA.

LC-MS analysis

To further prove that there is no difference between our IAA and standard IAA, we conducted LC-MS test. In Figure 9, the Zoom in shows the result of the two IAA. Both peak shows the molecular weight about 174. This is the IAA without a hydrogen atom. The molecular weight of IAA is 175.184. we believe that the two IAA is the same.