IGEM_TECCEM

Results

Sequencing

It is fundamental for us to make sure that all our BioBricks have the correct sequence before sending them to Boston for the parts registry. Therefore, we sequenced every single piece, to confirm that the ligated products into the pSB1C3 backbone correspond to the original sequence.

The BioBricks cloned by the iGEM TEC CEM 2017 team in PSB1C3 were sequenced in order to test if the inserts for the siRNAs and T7 terminator were really ligated. For the following samples of BSLA devices (Blue chromoprotein, forward siRNA, loop and reverse siRNA): 1, 2, 3, 4 and 5 the sequencing was made using the VF2 primer. Although it was possible to confirm the presence of the blue chromoprotein, the reaction couldn´t show us the presence of the siRNAs constructs because of the length of the protein gene before them. In these cases, a reaction using the VR primer is recommended since there are approximately in each case a total of 220-230 pb since the reverse primer to the siRNAs constructs.

The single presence of the siRNAs sequence (5’-3’) in PSCB1C3 without all the machinery (blue chromoprotein, loop and siRNA anti sense) was confirmed for the RacI and SOD constructs. The Wnt construct wasn’t sequenced and the results for the Awd construct weren´t conclusive. Also, the presence of the sequenced used as the control of the siRNAs (CNT) was confirmed to be cloned in PSB1C3 (sample 7). The sample 8 correspond to the single sequence of the T7-Terminator used during the construction of the BSLA devices, it was confirmed to be cloned in the PSB1C3. For the samples of BSLA device, we have to repeat the sequencing using the VR primers for the BSLA-SOD and BSLA-RACI, so for this samples we have the sequence forward and reverse with the objective to seek the siRNA construction before the blue chromoprotein, however the results weren't conclusive since the alignment showed the correct base pairs just after the reverse primer but not the same sequence before the terminator. And finally the sequencing for BSLA-AWD in PSB1C3 wasn’t repeated, since it was given to the team by the Gene script sponsorship, and once cloned in PSB1C3 the colonies became blue.
*All the samples were sequenced in a ABI PRISM 310 equipment

Blue BSLA colonies

The following figures show blue fluorescent colonies of E. coli HT115. The color of the bacteria represents the presence of the BSLA construct and production of siRNA.

Figure 5. First transformation in DH5a of the BSLA-AWD device from Genscript. The characteristic blue color from the blue chromoprotein is observed in the colonies.

Figure 6. First transformation in DH5a of the BSLA-AWD device in PSB1C3. The characteristic blue color from the blue chromoprotein is observed in the colonies.

Figure 7. First transformation in HT115 of the BSLA-AWD device in PSB1C3. The characteristic blue color from the blue chromoprotein is observed in the colonies.

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Figure 7. First transformation in HT115 of the BSLA-AWD device in PSB1C3. The characteristic blue color from the blue chromoprotein is observed in the colonies.

Real Time PCR

Now knowing that our siRNA molecules generate all the expected products (except RacI), we proceeded to the qRT-PCR, which allowed us to measure the amount of mRNA for the corresponding genes at any given time in the cells. We used SYBR Green as an intercalating agent and got the following results. The experiment results were divided on three groups:

Experiment A: We performed the soaking method with all the siRNA, the synthetic ones; AWD and RAC1. The ones we created using our raw BSLA Method; SOD and WNT. The purified samples of SOD and WNT, the sp and wp stand for pure. And finally a mix of RAC1, WNT, AWD and SOD to learn about the expression when these siRNA are mixed.

Experiment B: By applying chitosan to the leaves and feeding the diaphorina we tested two genes RAC1 and AWD.

Experiment C: We tested different concentrations to observe which one was the best option for our essay, we also performed this experiment in order to prove our mathematical modeling.

The following figures represent our Real Time PCR results.

Figure 8: Effect of the different siRNA molecules over the mRNA production in Diaphorina citri after in vivo soaking application.

Figure 9: Effect of the siRNA molecules mix over the mRNA production in Diaphorina citri after in vivo soaking application.

Figure 10: Effect of the chitosan-encapsulated siRNA molecules over mRNA production in Diaphorina citri after direct application over the plant leaves.

Figure 11: Effects of different concentrations (ng/uL) of siRNA-AWD tested in Diaphorina citri after in vivo soaking application to prove the proposed mathematical modeling.

The results from Figure 8 show that both synthetic and E. coli HT115 produced siRNA molecules were able to hybridize with its target sequence, inducing effective gene silencing by reducing the mRNA production. As it can be appreciated, the WNT siRNA reduced its target mRNA up to three times, being the highest-impact molecule, followed by AWD.

Figure 9 shows the effect of treating the psyllids with a mixture of the different siRNA molecules rather than with each siRNA separately. Once again, the WNT gene showed the strongest level of mRNA reduction, but in a much higher scale than with the solo treatment. The AWD siRNA is second, with almost the same impact as in the previous figure. The importance of this graph relies within the siRNA molecules for WNT and SOD produced with the novel BSLA BioBrick in Escherichia coli HT115 are functional on their own, which means that the BSLA has a great potential for future siRNA production in bacterial systems. It is important to notice that the siRNA have a higher activity in the Diaphorina citri mRNA production when applied together in a mix rather than individually.

The results observed in Figure 10 give us crucial information about the possible upscaling of our project via chitosan-encapsulated siRNA molecules and their direct application over the plant leaves. The main question was if the psyllids were attracted to the molecules and could feed on them. Since we observe reduction in the levels of mRNA, we can say that Diaphorina citri in fact fed on the chitosan. When comparing the treated psyllid with the negative control, it can be concluded that the AWD siRNA has the greatest reduction of the mRNA, while RacI has a lower direct impact in the mRNA expression.

In Figure 11, we tested different concentrations of the AWD siRNA to prove the mathematical modeling. All the concentrations yielded mRNA change expressions in the psyllids, but the most effective one was 60 ng/uL, followed by 20 ng/uL. The math model was developed to graph amount of siRNA to mRNA expression this helps us validate the results by analyzing the reduction of this expression, it also helps us determine which is the best concentration to be used to control the HLB plague.

Two-Step Quantitative Reverse Transcriptase PCR

Table 1. Expected products for the amplifications in the Two-step RT-PCR.

Product	Expected size
Tubulin	195 bp
Rac I	193 bp
WNT	200 bp
AWD	180 bp
SOD	199 bp

Figure 12. 2.5 % agarose gel with TBE Buffer 1X for the RT-PCR. The gel was loaded with Fast Ladder in lane 2 and 8 and with the samples listed in table N. The gel was stained with GelRed and run for 60 minutes at 100 volts.

As we can see in the figure, all the products for the Tubulin, AWD, SOD and WNT rely within the 0.150 and 0.300 kb marker bands, corresponding to the expected base pair sizes. The only product that remains outside the expected size is the RacI amplification product, which was observed in last week’s gel. The primers when tested in silico using PrimerBlast show the 193 bp product, but this does not happen in the gels. Since the reported sequence states “like-sequence” it is possible that there are mismatches between the reported sequence and the real one. It is still unclear why do the primers not generate the expected product. There are other predicted sequences such as XM_008482020.1 and XM_017443825.1, as this sequences are not specific the primers do not amplify this sequences either.

Diaphorina citri primary cell culture

The main objetive was to develop a primary culture of Diaphorina citri cells, to be transfected with our siRNA and analyzed through flow cytometry. The transfected siRNA sequences were tagged with Alexafluor so they would be visible. This protocol was repeated several times under different conditions, and different compositions of the culture medium were used, which can be seen below. The cells that were cultured in Medium B were able to survive after twelve hours, and replicated at a slow rate. Because of this, the flow cytometry was not performed.

Reagent	Medium A	Medium B
200 mM L-Glutamine	1 mL	1 mL
Penicillin and Streptomycin 1000X	1.5 mL	1.5 mL
Fungizone 500X	0.2 mL	0.2 mL
Schneider Medium	72 mL	80 mL
199 Medium 10X with Hanks’ salts	6 mL	-----
Fetal Bovine Serum (heat-inactivated)	20 mL	20 mL
0.06 M Histidine solution	1 mL	-----

Figure 1. Cell culture 12 hours after extraction.

Figure 2. Cell culture 2 days after extraction, observed under an inverted microscope at 10x. No significant cell replication can be observed compared to the first day,

Figure 3. Cell culture 2 weeks after extraction, observed under an inverted microscope at 10x. Cell replication can be observed.

Diaphorina citri laboratory development

Special cages were built for rearing and reproduction of Diaphorina citri specimens across three months. Each cage was double lined with fine white mesh to prevent the insects from escaping while allowing us to inspect them. On top, a set of bulbs was placed and connected to a timer, to control daily light hours, which were set at 16 hours of light and 8 of darkness. Additionally, two fan heaters were placed at a distance of 1 meter, which increased the temperature inside the cages to up to 30ºC. While this is not the ideal temperature for reproduction, the presence of eggs and nymphs could be observed after two weeks.

The initial population across all cages was of 80 insects, and after approximately one month an increase of almost double was observed. However, due to the psyllid's lifespan, a rapid decline was observed shortly after. In addition to this, the increase in population made it harder for each psyllid to feed on one plant, which increased mortality.

Figure 1. Detail of mesh lining the interior of the cages. The size of the mesh prevents the insects from escaping while providing light, air flow and visibility.

Figure 2. Presence of dew in the plant's leaves, resulting from nymphs feeding on the plant, which indicates reproduction.

Figure 3. Detail of plant leaves after two weeks of rearing. The presence of eggs in the stems of the plant can be observed.

Figure 4. Complete set-up for rearing of Diaphorina citri, consisting in two mesh-lined cages and complete with light and temperature conditioning.

Figure 5. Presence of adult Diaphorina citri specimens after one month of rearing.

Morphology

Different specimens were observed under a stereoscopic microscope and identified by gender.