Variegation Genetics
If you're arrived on this page and haven't checked out the previous posts full of background information, you may want to do that. In order:
Phylogeny: Who's related to who? (Echeveria vs. Sedum)
Hybrids: Cross-breeding (Mendelian genetics, how-to, and flower basics)
Variegation Genetics: YOU ARE HERE
Hybridization: Ploidy (compatible ploidy and hybrids)
A while back, I bought a Echeveria Purple Pearl, a sister plant of the Perle von Nurnberg, at the nursery. I noticed that some of the leaves seemed to be split down the middle or close to the middle, where one side was green/blue and the other purple/pink. I assumed that because the line was so straight, it must have been some straight object blocking the light on that particular leaf. However, after leaf propagating my succulent, the variegation has continued!
Someone else has found the same phenomenon on their Echeveria Perle von Nurnberg shown below.
Be aware that variegation is genetic and does not have to do with its living conditions. If the lighting conditions suddenly change, be prepared for a color change as well. Behold! My Perle von Nurnberg that was in the bright outdoors, then taken to my dark room:
The color change in this plant was due to anthocyanins. So why is this variegation happening in some plants and not in others?
Before we continue, I should probably mention my relevant two part series on how succulents are related (phylogeny: succulent family trees) and how hybridization (crossbreeding) works.
The Genetics of Variegation
While there are others ways for variegation to occur (random, viral, etc.), we will only be focusing on genetic variegation where the plant can make offpspring with the same pattern.
Leaf variegation is a recessive trait in higher plants (more complex plants like trees, succulents, etc.) The phenotype or the physical trait of variegation is only inherited maternally and it follows Mendelien genetics. You can click here to read about these vocab words and how Mendelien genetics works.
Variegation is caused by a genetic defect in the apical meristem. The apical meristem is a region of actively dividing cells. Here, there is an apical meristem at the root cap and also at the tip of the plant stem. We're talking about the top of the plant stem, where the leaves are actively being produced. This defect makes the development of chloroplasts unstable, such that some cells lack chlorophyll. (Chlorophyll is the green pigment in the thylakoids of chloroplasts. It is what makes plants green.)
Will the offspring have variegation?
You can always propagate by leaf pulling to see if the variegation is retained. Mathematically speaking, it should be, though no guarantees. If you're wondering how to make variegation appear when it is inherited maternally, and you have no idea what parts of the plant are female or male, read this.
Where is this genetic mutation located?
It is located on both/either chloroplast DNA or mitochondrial DNA. Variegation has been linked to both. As higher plants evolved, scientists believe that they may have developed redundant mechanisms to deal with over-photosynthesizing (the prevention is called photoinhibition). Some of the genes have been linked to the chloroplast while others have been linked to the mitochondria.
Why is there DNA in chloroplasts and mitochondria? I thought DNA was only located in the nucleus!
The endosymbiotic theory is here to explain all of this. Click here for a website that dives deeper into it than I will here. Endosymbiotic theory in a nutshell: fossil records indicate that bacterium (single-celled organisms with circular DNA) existed a long long time ago. Some of these bacterium were able to breathe oxygen (mitochondria precursor), while another kind was able to photosynthesize (chloroplast precursor). As organisms evolved, larger cells enveloped these bacteria and adopted them as their own organelles. Endo means inside of, and symbiotic describes a relationship where one benefits from the other. Evidence for this theory includes the fact that both chloroplasts and mitochondria have their own separate DNA from the cell nucleus so that they can produce proteins they need to function, as well as the fact that both of them have a double membrane.
BONUS: Are you into succulents, biology, botany, or science in general? How about a cute little plushy chloroplast or mitochondria to snuggle at night? A great gift for any organelle-inclined person. You can order them here from Fresh Crayons on Etsy. Each plushy is hand-made by Shari Bodofski (she studies molecular genetics!). You can follow her Instagram for a look at her work.
References
Sakamoto, Wataru. "Leaf-variegated mutations and their responsible genes in Arabidopsis thaliana." Genes & genetic systems 78.1 (2003): 1-9.
https://www.desertsun.com/story/life/home-garden/maureen-gilmer/2014/05/24/variegates-cacti-plants-desert-uv-rays/9530957/
http://hortsci.ashspublications.org/content/32/5/773.full.pdf
https://learn.genetics.utah.edu/content/cells/organelles/
Phylogeny: Who's related to who? (Echeveria vs. Sedum)
Hybrids: Cross-breeding (Mendelian genetics, how-to, and flower basics)
Variegation Genetics: YOU ARE HERE
Hybridization: Ploidy (compatible ploidy and hybrids)
A while back, I bought a Echeveria Purple Pearl, a sister plant of the Perle von Nurnberg, at the nursery. I noticed that some of the leaves seemed to be split down the middle or close to the middle, where one side was green/blue and the other purple/pink. I assumed that because the line was so straight, it must have been some straight object blocking the light on that particular leaf. However, after leaf propagating my succulent, the variegation has continued!
Someone else has found the same phenomenon on their Echeveria Perle von Nurnberg shown below.
 |
| Photo via reddit.com |
 |
| This is NOT variegation! |
Before we continue, I should probably mention my relevant two part series on how succulents are related (phylogeny: succulent family trees) and how hybridization (crossbreeding) works.
The Genetics of Variegation
While there are others ways for variegation to occur (random, viral, etc.), we will only be focusing on genetic variegation where the plant can make offpspring with the same pattern.
Leaf variegation is a recessive trait in higher plants (more complex plants like trees, succulents, etc.) The phenotype or the physical trait of variegation is only inherited maternally and it follows Mendelien genetics. You can click here to read about these vocab words and how Mendelien genetics works.
Variegation is caused by a genetic defect in the apical meristem. The apical meristem is a region of actively dividing cells. Here, there is an apical meristem at the root cap and also at the tip of the plant stem. We're talking about the top of the plant stem, where the leaves are actively being produced. This defect makes the development of chloroplasts unstable, such that some cells lack chlorophyll. (Chlorophyll is the green pigment in the thylakoids of chloroplasts. It is what makes plants green.)
Above: Chloroplast plush toys! The stacks of disks (thylakoids) are called grana (sing. granum)
You can always propagate by leaf pulling to see if the variegation is retained. Mathematically speaking, it should be, though no guarantees. If you're wondering how to make variegation appear when it is inherited maternally, and you have no idea what parts of the plant are female or male, read this.
Where is this genetic mutation located?
It is located on both/either chloroplast DNA or mitochondrial DNA. Variegation has been linked to both. As higher plants evolved, scientists believe that they may have developed redundant mechanisms to deal with over-photosynthesizing (the prevention is called photoinhibition). Some of the genes have been linked to the chloroplast while others have been linked to the mitochondria.
Why is there DNA in chloroplasts and mitochondria? I thought DNA was only located in the nucleus!
The endosymbiotic theory is here to explain all of this. Click here for a website that dives deeper into it than I will here. Endosymbiotic theory in a nutshell: fossil records indicate that bacterium (single-celled organisms with circular DNA) existed a long long time ago. Some of these bacterium were able to breathe oxygen (mitochondria precursor), while another kind was able to photosynthesize (chloroplast precursor). As organisms evolved, larger cells enveloped these bacteria and adopted them as their own organelles. Endo means inside of, and symbiotic describes a relationship where one benefits from the other. Evidence for this theory includes the fact that both chloroplasts and mitochondria have their own separate DNA from the cell nucleus so that they can produce proteins they need to function, as well as the fact that both of them have a double membrane.
BONUS: Are you into succulents, biology, botany, or science in general? How about a cute little plushy chloroplast or mitochondria to snuggle at night? A great gift for any organelle-inclined person. You can order them here from Fresh Crayons on Etsy. Each plushy is hand-made by Shari Bodofski (she studies molecular genetics!). You can follow her Instagram for a look at her work.
References
Sakamoto, Wataru. "Leaf-variegated mutations and their responsible genes in Arabidopsis thaliana." Genes & genetic systems 78.1 (2003): 1-9.
https://www.desertsun.com/story/life/home-garden/maureen-gilmer/2014/05/24/variegates-cacti-plants-desert-uv-rays/9530957/
http://hortsci.ashspublications.org/content/32/5/773.full.pdf
https://learn.genetics.utah.edu/content/cells/organelles/
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