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Post by aineo on Aug 24, 2014 16:47:16 GMT -5
I have several ears of corn this year that have streaks of color in them. I deliberately saved seed, and replanted that seed, last year that had this trait, but now I am wondering if it is possible to grow corn for this trait or if it is just luck. It seems the reason for the streaks is jumping genes or transposons. I have found that mentioned in some threads here, but I have yet to see whether that is a trait that can be bred into corn, or as said above, is it just luck? Or, perhaps it is a trait one wouldn't want. I have tried to read through some material on the Internet (like this one: www.nature.com/scitable/topicpage/barbara-mcclintock-and-the-discovery-of-jumping-34083), but I don't have enough understanding to know what I am reading. Is there anyone here that can help? Here are a few pics. Oh, by the way, these are decendents of Joseph's popcorn.
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Post by philagardener on Aug 24, 2014 18:37:41 GMT -5
Pretty ears, @ aineo ! The maize genome is full of transposons ("jumping genes" or "mobile genetic elements") and they move around frequently. This activity can generate new mutants in a variety of traits (features) as genes are interrupted or restored and likely explains the plasticity that allowed modern maize to be selected so quickly (in relative terms) from an ancestor like teosinte. In a way, transposon activity is natural genetic engineering, and gardeners simply select for or against the outcomes (as with any mutation, only transposon mutants can be unstable and change again as I will explain below). Transposon activity is particularly easy to see in maize seeds as there are several different pigmented layers (pericarp, aleurone, endosperm, etc.), and different kinds of transposons can generate different patterns (such as patches and streaks - both visible in your pictures) in different tissues. Understanding a lot of this was Barbara McClintock's life work and such a breakthrough that she was awarded a Nobel Prize. In very straightforward terms, say you have a gene for an enzyme that makes red pigmentation. When it functions in the cells of a kernel, the tissue is red. If a transposon moved into that gene, it can be interrupted ("broken"), and the red pigmentation cannot be made, so the tissue instead would be white. Plant that white kernel and in the next generation the transposon may move again - so from a white seed you can get a red one (if it moved) or another white one (if it didn't). Kernels of different colors! Now if the transposon moved early during seed development, the descendents of that cell would be red or white against a background of cells in which the transposon didn't move (which would be the other color). That is how you get kernels with patches and streaks. The larger the colored area, the earlier the movement happened; small patches (sectors) happen later in development. So the patterns can tell an interesting story about how the seed grows. Transposons can stay in place for generations, or move very frequently during the life of a single plant. So effects can be gained, lost, and even reappear suddenly after years. Of course, this distills things down to most basic terms (so I'm glossing over a lot!). Because cells have two copies of each gene ("diploid" - three in "triploid" endosperm) and there are multiple genes and biochemical pathways for different pigments, it gets complex quickly, particularly in seeds where genes come from both the mother plant and different pollen donors. It is also true that the attractiveness of these patterns means that transposon-influenced traits have been selected for many generations, resulting in the riot of colors and patterns that you see in your lines. It all really is a-mazing!
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Post by oxbowfarm on Aug 24, 2014 19:18:43 GMT -5
You have a couple of different things going on in those photos.
The striped effect is due to chinmark pattern pericarp pigmentation. That is maternal tissue and is expressed by the mother plant. Every kernel on the cob will be chinmark because the mother plant's genome is expressing chinmark, but chinmark expresses slightly variably on individual kernels, but that is not due to transposons from my understanding. Where transposons come in is sometimes the transposon will insert and express only partially in one ear, and you will have a block of kernels without any pigmentation because the transposon turned off pericarp pigment expression. An un-pigmented pericarp kernel from such an ear has the same likelihood of expressing chinmark as any other kernel on that cob.
The other thing that is showing is some darker aleurone color showing on individual kernels due to xenia with different kernels having different genetics for aluerone color.
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Post by raymondo on Aug 24, 2014 23:31:41 GMT -5
Regardless of the cause, the cobs are lovely to gaze upon.
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Post by aineo on Aug 25, 2014 5:59:42 GMT -5
Thanks for all the information everyone. I agree, raymondo, regardless of the cause, they are lovely to gaze upon.
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Post by 12540dumont on Aug 26, 2014 16:40:45 GMT -5
I'd like to say that Maize is not descended from teosinte. It's descent is from pod corn crossed with teosinte. And corn can be continually crossed with teosinte. Which it often is in Mexico. See "Races of Maize Mexico" Here's a simplified discussion: waynesword.palomar.edu/transpos.htmIsn't corn fun? Verra Purdy Aineo!
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Post by philagardener on Aug 26, 2014 19:12:11 GMT -5
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