Recently a member here told me about some important developments in molecular genetics that I was unaware of. These developments were pretty well publicized (they were also discussed some here at ICMAG) because they significantly advance our understanding of genetics, and have important practical applications that could revolutionize the way we harness plants to do our bidding. I don't know how I missed this, it got under my radar somehow. Thanks to the member who brought this to my attention!
Here are the two papers that got national press a while back:
Haploid plants produced by centromere-mediated genome elimination
Synthetic Clonal Reproduction Through Seeds
The first paper, about haploid plants, tells how the authors developed a technique that would allow for the creation of plants that were perfectly homozygotic for all traits. This technique does not involve breeding over numerous generations, perfectly homozygous plants are created in a two-step process. This could be a gigantic breakthrough in plant breeding.
In the second paper, about the "clone seeds", the authors have successfully induced apomixis in plants that are not normally apomictic. This allows for the production of seeds that have not undergone the "card shuffling" of meiosis, and are identical genotypically to the parent. This too is a mind-blowing advance.
This thread is not to discuss the two papers above, but to discuss the key feature that both techniques rely on. Both techniques depend on the use of a mutant plant that the authors developed.
cenh3 null mutation
Plants with the cenh3 null mutation can fertilize another plant without passing on any of it's own genetic material! This mutant was developed while investigating the structure/function relationships of a single gene that codes for the centromere specific histone CENH3. It was not anticipated that this particular mutation would have the properties is does.
The creation of the cenh3 null mutation was first reported in this paper:
The Rapidly Evolving Centromere-Specific Histone Has Stringent Functional Requirements in Arabidopsis thaliana
(EDIT: This paper wasn't the first, the "Haploid plants produced by centromere-mediated genome elimination" was the first to mention the haploid inducer. I think when they discovered the haploid inducer in the process of doing the research for this "Rapidlly Evolving... " they published on the haploid inducer before they were done with the study. Sorry about the confusion on my part.)
This paper investigates how changes in the CENH3 gene affect its function. They wanted to find out what structural features of the resultant histone were the most important. The CENH3 gene in the test plants was replaced with CENH3 genes from other species (including humans) and artificially created chimerical CENH3. The results of these replacements would give clues to which portions of the gene conferred function.
In order to test these gene replacements, they had to have a plant that was a blank slate for this gene, so they knew it was the inserted gene that was being expressed. They were successful in creating this mutant, named cenh3 null. The original gene still exists in this mutant, but is truncated in a way that makes it completely non-functional.
In the course of using the cenh3 null mutant to probe CENH3 structure-related function, the researchers discovered (by accident) that it could fertilize another plant and produce offspring that contained none of the genetic material of the mutant!
Among other uses, this mutant can be used to produce haploid plants in one step, just by crossing the subject with the cenh3 null mutant. Because of this the researchers call the cenh3 null mutant a "haploid inducer". The haploid is then converted to diploid with colchicine or another ploidy multiplying substance to obtain a perfectly homozygous plant.
The significance of having haploid inducing plants is enormous.
For one thing, the diploid plants resulting from doubling the haploids are perfectly homozygous in a way that a conventionally bred plant could never be.
For another thing, once you have the haploid inducer for a species, it would be capable of producing haploids, and therefore homozygotic diploids of any individual plant in the species. You could take any plant with traits you liked, cross it with the haploid inducer, double the results and be left with a bunch of perfectly homozygous plants. The ones with traits you liked would be perfectly true-breeding in a way that a normally bred plant could never be.
The second paper about "clone seeds" uses the haploid inducer along with another important new mutant. I won't discuss this other mutant now, other than to say that it is a mutation that converts the process of meiosis to mitosis in the mutant. This produces seeds that bypass the allele shuffling of meiosis. If that doesn't blow your mind, nothing will!
In my next post I will explore how the researchers created this fabulous haploid inducer.
Here are the two papers that got national press a while back:
Haploid plants produced by centromere-mediated genome elimination
Synthetic Clonal Reproduction Through Seeds
The first paper, about haploid plants, tells how the authors developed a technique that would allow for the creation of plants that were perfectly homozygotic for all traits. This technique does not involve breeding over numerous generations, perfectly homozygous plants are created in a two-step process. This could be a gigantic breakthrough in plant breeding.
In the second paper, about the "clone seeds", the authors have successfully induced apomixis in plants that are not normally apomictic. This allows for the production of seeds that have not undergone the "card shuffling" of meiosis, and are identical genotypically to the parent. This too is a mind-blowing advance.
This thread is not to discuss the two papers above, but to discuss the key feature that both techniques rely on. Both techniques depend on the use of a mutant plant that the authors developed.
cenh3 null mutation
Plants with the cenh3 null mutation can fertilize another plant without passing on any of it's own genetic material! This mutant was developed while investigating the structure/function relationships of a single gene that codes for the centromere specific histone CENH3. It was not anticipated that this particular mutation would have the properties is does.
The creation of the cenh3 null mutation was first reported in this paper:
The Rapidly Evolving Centromere-Specific Histone Has Stringent Functional Requirements in Arabidopsis thaliana
(EDIT: This paper wasn't the first, the "Haploid plants produced by centromere-mediated genome elimination" was the first to mention the haploid inducer. I think when they discovered the haploid inducer in the process of doing the research for this "Rapidlly Evolving... " they published on the haploid inducer before they were done with the study. Sorry about the confusion on my part.)
This paper investigates how changes in the CENH3 gene affect its function. They wanted to find out what structural features of the resultant histone were the most important. The CENH3 gene in the test plants was replaced with CENH3 genes from other species (including humans) and artificially created chimerical CENH3. The results of these replacements would give clues to which portions of the gene conferred function.
In order to test these gene replacements, they had to have a plant that was a blank slate for this gene, so they knew it was the inserted gene that was being expressed. They were successful in creating this mutant, named cenh3 null. The original gene still exists in this mutant, but is truncated in a way that makes it completely non-functional.
In the course of using the cenh3 null mutant to probe CENH3 structure-related function, the researchers discovered (by accident) that it could fertilize another plant and produce offspring that contained none of the genetic material of the mutant!
Among other uses, this mutant can be used to produce haploid plants in one step, just by crossing the subject with the cenh3 null mutant. Because of this the researchers call the cenh3 null mutant a "haploid inducer". The haploid is then converted to diploid with colchicine or another ploidy multiplying substance to obtain a perfectly homozygous plant.
The significance of having haploid inducing plants is enormous.
For one thing, the diploid plants resulting from doubling the haploids are perfectly homozygous in a way that a conventionally bred plant could never be.
For another thing, once you have the haploid inducer for a species, it would be capable of producing haploids, and therefore homozygotic diploids of any individual plant in the species. You could take any plant with traits you liked, cross it with the haploid inducer, double the results and be left with a bunch of perfectly homozygous plants. The ones with traits you liked would be perfectly true-breeding in a way that a normally bred plant could never be.
The second paper about "clone seeds" uses the haploid inducer along with another important new mutant. I won't discuss this other mutant now, other than to say that it is a mutation that converts the process of meiosis to mitosis in the mutant. This produces seeds that bypass the allele shuffling of meiosis. If that doesn't blow your mind, nothing will!
In my next post I will explore how the researchers created this fabulous haploid inducer.
).
