I wonder how often chimerism affects the outcomes of crosses between roses.
It affects human heredity: https://www.washingtonpost.com/news/morning-mix/wp/2015/10/30/the-ghostly-explanation-for-how-a-mans-unborn-twin-fathered-his-child/
Peter
Wasn’t that fascinating? Creepy, but fascinating!
Yes, I read the article too. I found it fascinating and my reaction was there is still so much we don’t know about the human being which is STILL very much a mystery. That is why I get so angry when the far right thinks human life should be like like the DIck and Jane reader which I learned to read from in 1st grade.
For those of you who are too young Dick and Jane were a brother and sister (I think Jane had blonde hair and blue eyes) with a mommy and a daddy (white, assumed Protestant) and their dog Spot(a cocker spaniel which was the #1 popular breed at that time.) Don’t get me wrong, I loved my Dick and Jane stories but no one could have been farther from Dick and Jane than me and a whole lot of other people. There are many people outside the socalled “normal”, and they are still human beings. This story so perfectly illustrates this. I just wish Americans of certain political and religious persuasions would read this and finally realize that not every human being fits the narrow pattern of Dick and Jane’s family.
My apologies for getting off our usual wonderful discussions of roses but when I first read this wonderful article, it made me again realize that all human beings do not fit into the narrow Dick and Jane pattern, lovely though it is. I once read a book on genetic aberrations with pictures and one would be amazed at the number of people born outside the “box.”
I read the posts on here at least once a day but rarely post. I just thought it such a wonderful article and hope that more people will get to read it and its implications for us in the modern world. Of course we are familiar in many ways with all the genetic unknowns in our quest for creating the “perfect” rose.
Happy Hallowe’en to all and I hope I have not offended anyone.
Jim (who feels like a great big pumpkin at this point!)
Boy, I do not find this creepy at all, but it certainly does underscore the complexity of genetics. I have read about another case similar to this and it can throw a monkey wrench into what one thinks is true and what is actually true. A great and hopefully eye opening article.
Peter,
I read a similar article, years ago, about a woman who was informed that two of her three sons were not hers … even though she had given birth to them, and her husband was the father.
http://www.katewerk.com/chimera.html
“In a forthcoming paper in the journal Arthritis & Rheumatism, they describe how they took blood samples from 32 healthy women and found that 22 per cent of them were carrying white blood cells from their mothers.”
As for roses, I’ve read that ‘Chevy Chase’ can sport to pink when pruned closely. This suggests that CC is a chimera, and that either type (pink or red) might be the parent of any offspring.
Some color sports tend to revert, which might result from chimerism. The first sport I ever saw happen was a red-flowered form on the white-flowered ‘Dagmar Spath’, itself a sport from the magenta ‘Lafayette’.
When looking for a single trait, the simplest explanation for sports is “jumping genes”, that is some kind of transposable elements that move in or out of select locations in regulatory positions of different genes. The repeat-blooming "gene, is actually an insertion that disrupts a gene that controls once-flowering. Color sports usually change intensity of color, due to up or down regulating the expression of some gene needed to make a certain color. At times it can uncover an alternate color, as when the R. foetida goes back and forth from yellow to red on the inner surface of petals.
With white being the absence of color, the appearance of pink or red means that a gene that had been silenced, is regaining its expression pattern. It is important to recall, as I often forget to do, that anthocyanins which make red, are often expressed in leaves, cotyledons, petioles and only in selected portions of flowers. Most of the time we don’t see red stigmas, styles, pistils or filaments. But sometimes we do. Red petals may be linked to these colored parts often but by no means always. Lots of yellow roses, indeed some of the most attractive, have red in their inner reproductive parts. So it is probably not chimerism in the traditional broad sense, but very selective gene switching that determines whether flowers or flower parts have one color or another.
True chimeras could certainly happen if two gametes from pollen, make contact with an egg simultaneously. Then you’d have 4 nuclei, 2 from each pollen grain. Half of them could get lost, one would make endosperm and the other the embryo. Once in a while, they might swap chromosomes or chromosome parts. In roses the endosperm is very minor. In cereal grains it is prominent. So we’d have a better chance of seeing that effect in something like maize.
Triploids are in a sense chimeras as they make choice every generation on whether to be diploid, tetraploid or aneuploid, when they produce eggs and pollen. The phenomenon of HT type flowers on what is clearly a rugosa or foetida type shrub is much like the perceived human chimeras. But, so far no one has tested for the actual DNA complement of the total chromosomal set of such odd hybrids, so far as I know. Conrad F Meyer would be an example.
Larry,
Has such a transposon (jumping gene) been identified in Rosa foetida?
An alternative explanation is that sometimes a gene finds itself (e.g., following a translocation) at the boundary between euchromatin and heterochromatin. As the boundary shifts, the gene is silenced, unsilenced, silenced, unsilenced, etc. This model seems a better fit than transposons for striping.
Chimeras also may occur where the fertilized ovum is trisomic, but one of the extra chromosomes is lost. For example, suppose the fertilized ovum received two copies of the chromosome carrying the “gene for crimson” and one from the white-flowered parent. In one cell-line the “white-flowered” chromosome is lost, leaving that cell-line homozygous for crimson. In a different cell-line one of the “crimson-flowered” chromosomes is lost, leaving it heterozygous (pink-flowered). In such a case, it would be helpful to look at more than flower color.
Journal of Genetics, 32: 117-170 (1936)
A Biochemical Survey of Factors for Flower Colour
Rose Scott-Montcrieff
p. 149. Rosa polyantha: An interesting spray of flowers from a sporting Polyantha Rose (‘Paul Krampel’) was recently sent by Mr R. E. Cooper of the Royal Botanic Garden, Edinburgh. While the normal flowers were scarlet two distinct mutations had occurred; one to crimson and the other to a dog-rose pink.
A chemical examination of the pigments involved showed that the normal scarlet flowers were deeply pigmented with pelargonin and some flavone, while in the two sports cyanin took the place of pelargonin, the pale pink flowers having a smaller amount of anthocyanin than either the scarlet or crimson flowers, together with a proportional increase in flavone content. All three types of flowers contained large amounts of tannin.
The mutation from scarlet to crimson thus involves a change in pigment to a more oxidized anthocyanin with a similar 3-5-dimonosidic residue, while the change from scarlet to pink appears also to involve co-pigmentation and a change in the anthocyanin-flavone balance, and is apparently due to a double mutation.
‘Orleans Rose’ has a peculiar chromosome structure that might be related to its “sportiness”.
There was an example of trisomy resolution in a pair of monozygotic human twin boys. One had lost the extra chromosome and appeared “normal”, while his brother retained it and expressed Down’s syndrome.
Another type of chimerism can occur following somatic meiosis. Pickard (1929) reported an example of this.
http://bulbnrose.x10.mx/Heredity/BUNNY.HTML
So far as I know there are very few transposons clearly identified in roses, other than the one that causes repeat blooming. But that doesn’t mean that they aren’t there.
As I understand it, there is only one reliable source for striping in the HT and related lines. Being located at a border sounds plausible in that case for making regular stripes. I was thinking of the photos on HMF and my own observations of partial flowers, or shoots where AC has reverted to AY. I think that is most simply explained as something popping in and out randomly in the meristem and rapidly differentiating cells that give rise to flower parts. Because AC and AY are sterile in the production of hips, we can’t do proper genetics to sort this out well.
For common color sports, I wouldn’t want to exclude methylation or other modifications that alter DNA transcription (which may be equivalent to the euchromatin/heterochromatin idea at the level of microscopy).
Karl, thanks for posting the Erlanson paper. Readers should be cautioned, however, that it represents the state of the art in 1931 and much more is known now, almost a century later. We need a molecular biologists to interpret this paper in that light.
Don,
That’s why I like to bring up the old stuff that is too often forgotten. Out of sight, out of mind.
And while I’m reminding about old stuff, there is an odd fact that cells can regulate their DNA quantity in ways that are sometimes annoying to experimenters.
In the early days of colchicine, it was not uncommon to read of colchicine sports or mutants. In some of the studied cases, the chromosomes had doubled as expected. But in some lines, as the cells duplicated their chromosomes again in preparation for mitosis, a cell detected an excess of DNA. To compensate, this cell-line inserted an extra division … which is equivalent to meiosis rather than mitosis.
In other words, a diploid cell duplicated its chromosomes in preparation for mitosis, but the colchicine inhibited spindle formation. The cell did not divide, and remained with twice the usual number of chromosomes. A mitosis or so later, the cell “freaked out” and divided twice instead of once, bringing about a somatic meiosis. Each of the resulting cell lines represented a distinct “colchicine sport”.
If the original diploid was heterozygous for red/white and double/single, the various colchicine sports might include double red, double white, single red, single white, and double or single pink. It is a matter of chance which one of these ends up in the outer layer of cells that determine the appearance of the new plant.
It is also possible to trick plants into inserting a second round of division. Sodium nucleate has been used, but it’s not available at the local pharmacy. Caffeine reportedly makes a useful substitute. In this way, tetraploids may sometimes be persuaded to give diploid sports. I suspect that these would be rather different from the diploid plants regenerated from pollen mother cells.
Still trying to wrap my head around this one that showed up in my yard a few years back…wish I knew then what I know now about propagation. Burgundy Iceberg (shown in photo on left) is known for it’s propensity to sport (sport in photo on right). I was amazed at the clarity of the color break border on the petals. I have this photo to remind me that it wasn’t a figment of my imagination.
[attachment=0]P1010051-1.JPG[/attachment]
Doug Wild
Beautiful photo. My amateur interpretation follows. First there was a cell that lost its burgendy expression. It was progenitor of a shoot (forming a bud plus some unknown number of leaves). Then the burgundy got switched back on very later in the process so that 3 petals, or petaloids, were in part reactivated. Might have carried through into a stamen also, and could have been in a sepal. Those probably wouldn’t show color anyway so we can’t tell.
Two years ago, or maybe 3, at the beginning of November, I found a shoot of Sunrise-Sunset with white flowers. That shoot had arisen after the bushes were heavily pruned in late August. Unfortunately I was only able to get roots on the lower portion of the shoot and it was not sportive. I was going to call it Snowy Sunrise. Still hoping for another chance.
Science and the Garden: The Scientific Basis of Horticultural Practice (2008)
Know your Plant by David S. Ingram
p. 70-71
“The activity of transposons can be seen in several common garden plants. Indeed, they have enjoyed some popularity in recent years with the fashion among breeders to produce flower varieties with randomly striped and spotted petals. The beautiful random red stripes and spots on the petals of one of our oldest rose varieties, > Rosa gallica > ‘Versicolor’ (> Rosa mundi> ), are the result of transposon activity. In fact careful examination of any collection of old rose varieties is likely to reveal some specimens with similar random patterning in the petals. The ancestor of > Rosa gallica > ‘Versicolor’ was a red rose that was carrying a transposon. At some point this transposon happened to insert itself into one of the genes involved in red pigment production. damaging the gene and preventing the production of pigment. This event must have happened in a germ line or meristem cell as it has been possible to propagate the resulting ‘sport’, a ‘white’ rose without pigment in the petals. However, this transposon has continued to move, and each time it does so it may restore the structure and activity of the pigment gene. As transposons are active within individual cells, only those cells where the transposon moves, and any daughter cells they produce will he capable of producing red pigment. If this happens during flower bud development in one of the cells that is involved in producing a petal, then when the flower opens a red spot will mark the presence of that cell and any daughter cells it produced after the transposon moved. If the transposon moved early in flower bud development then the affected cell will have produced many daughter cells. resulting in a large red stripe or spot on the opened petal. If the transposon was active late in bud development the cell will have divided only a few times before petal formation was complete and consequently only a small red spot will be evident. If the transposon is highly active, moving frequently, then there is a high probability that it will move in several cells in each petal during the period of bud development, and we would expect to see several spots and stripes on each mature petal. A less active transposon will move less frequently, the probability of it moving in more than one or two cells per petal during bud development will be small and so we would expect to see only a few spots and stripes per petal (Plate 9).”
I’m a little skeptical of this explanation. It is not necessary for a transposon to “jump” to be involved in variegation. In some cases the transposon is silenced, along with some genes located nearby. The variegation occurs when the state of the transposon and its neighbors (silenced vs active) changes.