Comments on: It’s been a good week for the genomes

By: Karl Haro von Mogel

Karl Haro von Mogel — Wed, 11 Nov 2009 04:43:31 +0000

I’ll pull the paper tomorrow once I’m back on the university network (and on the subscription), but that does seem to be the case. Note that in the part you quoted it described the (mostly) transgenic plants as being healthy – which implies that the diseased ones were simply that – diseased and unappetizing rather than dead.

By: Jeremy

Jeremy — Tue, 10 Nov 2009 15:44:41 +0000

Karl, are you sure that the plants containing the transgene are more attractive to cucumber beetles? I’ve a feeling that the reason they suffered more from cucumber beetle attack, and with it great spread of bacterial wilt, was that the virus-susceptible plants had died. The abstract says:

[A]s the virus spread through the fields, the cucumber beetles became increasingly concentrated upon the healthy (mostly transgenic) plants, which increased exposure to and the incidence of wilt disease on the transgenic plants.

By: Karl Haro von Mogel

Karl Haro von Mogel — Tue, 10 Nov 2009 15:38:15 +0000

I would like to point out that whether the viral resistance comes from a transgenic approach or by breeding in endogenous resistance, the issue with the cucumber beetles and bacterial wilt would be the same. (In wild squash, that is) Although you don’t say that these kinds of surprises don’t happen with breeding (which they do), it does seem to be implied by the last part of your post.
So that readers are clear – the paper on transgenic squash did not find that virus-resistance squash in agricultural fields were more susceptible to bacterial wilt – it instead found that in the wild, plants with this resistance were more attractive to cucumber beetles than virus-infected plants. And the beetles spread bacterial wilt. It is a property of the ecology, not of the resistance trait. Definitely read James’ post about the misunderstandings of the paper! (And I agree that Jeremy did not misunderstand it, but there’s the potential that others could from reading this.)
That being said, I would like to suggest that I think that the breeding-vs-engineering dichotomy falls flat on the submergence-tolerant rice developed by Pam Ronald et al example. In that case, simply breeding the trait over failed repeatedly. It wasn’t until they could pinpoint the gene responsible and demonstrate its effectiveness through transgenic approaches that it could be bred over reliably using marker-assisted breeding. And you would think that submergence-tolerance would be simple to select for (submerge it and see!), but what about the more complicated traits? In this example, molecular methods (including genetic engineering) and breeding go hand-in-hand. And that’s sexy.

We need more breeding, but not “ordinary” breeding. We need greater understanding of the genetics of the plants we grow, eat, and wear, which we can then apply to those plants. Association mapping, molecular markers, transgenes, cisgenes, RNAi, comparative genomics, compositional analyses, etc, these and more are going to be increasingly important. Complete genome sequences provide a road map for studying the genetics of those genomes – there are profound practical implications beyond the basic science involved.
Anyway, that’s my stump speech for genetics. Now back to the lab…

By: James

James — Mon, 09 Nov 2009 08:07:49 +0000

I’m not aware of any such studies either. I was excited to read the squash paper because it seemed to be the most detailed research into what would happen to a transgene in the wild up to this point, and was depressed to see it getting spun by others into something else when the actual result is so interesting in of itself. (Sorry for jumping the gun and assuming you’d seen the same spin.)

By: Jeremy

Jeremy — Mon, 09 Nov 2009 07:58:47 +0000

James, thanks for your comments. I very carefully weaseled out of saying that the transgenic squash were disadvantaged. “Plants that carry the resistance genes” was deliberately worded that way. The whole question of the survival of introgressed traits — engineered or otherwise — in the absence of selective pressures is, as I am sure you are aware, one of considerable uncertainty. For example, I would expect constitutive traits, where a gene is active all the time, to be much less stable than facultative ones, where the gene is switched on by some signal. But I’m not aware of any studies that demonstrate this.

Anyway, I’m glad you agree with my bigger point, that interesting though the genome studies are, conventional breeding is more important than ever.

By: James

James — Sun, 08 Nov 2009 21:29:21 +0000

To be fair, the study you cite is talking about wild squashes with the transgene introgressed. In an actually agricultural setting I presume the beetles are controlled with insecticides anyway which should sever the link between virus resistance and cucumber wilt. I tried to document how the findings of that article quickly spun out of control here But I absolutely agree conventional breeding is as important, if not more, as it ever has been. The improvements are faster, cheaper to get approved, and more fine-tuned than the current fruits of genetic engineering. After all the flood tolerant rice was created using marker assisted breeding after first being proto-typed with a transgenic construct. And for lots of additive traits, everything from yield itself to resistance to lodging, there's no substitute for plant breeders out in the field making improvements.