The original method of messing with genes is mutagenesis and screening. Screening is a big important concept to think about in biotechnology and we're going to use it throughout this project. The essential flavor of it is that biotechnology is very imprecise, but that's okay because we're working with billions to trillions of molecular machines. In the normal engineering shop, if you want to build a house, you source some well-made materials, make careful measurements and cuts using tools that you are trained on, and work according to a plan that you can follow as you build. In the biotech shop, the general idea is that you grow a few billion two by fours, throw in a million nails and hammers, mix well, and have a selection strategy for separating the one well-built house from the hundreds of thousands of piles of debris.
Crop scientists have been doing this since the 1930s: get piles of seeds, irradiate them, and then farmers plant them all and weed out the disgusting mutants and boring regular plants. Most of the grapefruit and peppermint crops in the US were developed using this process. Good magazine suggests that the reason that these foods don't have the bad rap that GMOs do is
1) Because there is no main list of modified crops or way to test for them / people don't know about them.
2) Because radiation mutagenesis is done almost entirely by big public sector institutions that publish their results and work for the public good.
Personally we feel that atomic scientists just have better style than genetic engineers.
Returning to our peppers: if you wanted to knock out and select for vanillin in this method, you would have to grow every plant to the point of producing fruits, then have some chemical or taste test to identify the very few plants that would produce it. You would have to produce a huge amount of plants and take them all the way to fruiting, and it would take you many, many years, which is why we aren't going to do it this way, although we wouldn't have to buy much in the way of equipment.
Engineers these days use what is called an interfering RNA. Remember the central dogma? As you are sitting there doing the hard work of enacting it, transposons and viruses are trying to get your cells to do it for them. Freeloaders! Most multicellular organisms have a protein in charge of kicking RNA out that doesn't belong, it's called RISC, and if it finds double stranded RNA, it tries to transcriptionally silence it through the cell. In plants this kind of silencing can be passed on through generations even without actually pushing it into the genome in some way. In order to get this into our plant, we have a few options.
In the simplest case, we can just make some dsRNA and inject it straight into a plant. We can get a foundry to print us up a 400-600 bp section of the gene, buy some RNA polymerase to produce the dsRNA, and shoot up a healthy plant before the RNA falls apart. This is reasonable, but what we have heard is that this kind of intervention may or may not be systematic or long-lasting. To be more sure that our interfering RNA is being continuously produced;
We can shoot a plant up with a virus containing a piece of the gene we want to knock out: this is called virus-induced gene silencing, and there are published results of someone doing just that in C. annuum.
We can try to integrate that interfering piece into the genome of our Capsicum species (using Agrobacterium or some other transformant) This has also been done.
Unfortunately neither of those papers are immediately accessible from our local university libraries, so there will be a gap until we can talk about exactly what they did.
Next time: we'll talk more about how to access the genetics of Capsicum, both online and in the fleshy pericarp.
No comments:
Post a Comment