Home » horizontal gene transfer, News » Horizontal gene transfer: Whole chloroplasts move between species; how they do it unclear as yet – researchers

Horizontal gene transfer: Whole chloroplasts move between species; how they do it unclear as yet – researchers

birch(left) - oak (right) graft. Sexually incompatible species can exchange chloroplast genomes at graft sites/Max Planck Institute

From “Genetic Information Migrates from Plant to Plant” (ScienceDaily, Feb. 1, 2012), we learn,

Plant scientists were confounded by the fact that the DNA extracted from the plants’ green chloroplasts sometimes showed the greatest similarities when related species grew in the same area. They tried to explain the phenomenon with the assumption that every once in a while those normally sexually incompatible species crossed and produced offspring with a new combination of nuclear and chloroplast genomes.

They coined the term “chloroplast capture” to illustrate what they thought was happening. Now, scientists around Ralph Bock from the Max Planck Institute of Molecular Plant Physiology in Potsdam discovered that a transfer of entire chloroplasts, or at least their genomes, can occur in contact zones between plants. Inter-species crossing is not necessary. The new chloroplast genome can even be handed down to the next generation and, thereby, give a plant with new traits. These findings are of great importance to the understanding of evolution as well as the breeding of new plant varieties.

For a long time, scientists believed that HGT was restricted to prokaryotes, organisms without nuclei. It was universally accepted that, for example, bacteria can exchange genes that are crucial to their survival, like the ones that transmit a resistance to antibiotics. Nowadays it is increasingly appreciated that HGT is in fact not restricted to prokaryotes. It can be observed at the contact zone between different animal tissues after an organ transplantation or — as shown here — between two fusing plants.

“As of now, we do not know how chloroplasts manage to get from one cell to the other,” says group leader Ralph Bock. “But the decisive point is that it happens and the discovery of this process offers a new explanation for important evolutionary processes and opens up new possibilities for plant breeders.”

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6 Responses to Horizontal gene transfer: Whole chloroplasts move between species; how they do it unclear as yet – researchers

  1. This one makes me happy though. I’ve held for ages that the stochastic notion required HGT. Makes phylogeny a nonsense. But it’s nice to see that the religious fundamentalists are starting to acknowledge empiricism and logic.

  2. I’ve held for ages that the stochastic notion required HGT.

    Why?

    Makes phylogeny a nonsense.

    Hardly. The strong signal of the nested hierarchy dwarfs any confounding due to HGT.

  3. Well, no, it doesn’t “make phylogeny a nonsense”. But it does explain why, the genetic phylogenies don’t map precisely on to the morphological ones. Reproductive success is a function of the phenotype, not the genotype.

    And of course, what is interesting, is that HGT provides a superb way of confirming certain phylogenies, because we can track HGT insertions at specific locations through a lineage, on the assumption that an HGT insertion at a specific location represents a single event in a single individual, from whom all individuals with that insertion descended, and that mutations in that insertion will map the branching from that original organism down the lineage.

    But you are right that HGT is another source of stochastic variation in DNA sequences, and therefore, sometimes, in phenotypic variation. I’m sure there are many more yet to be discovered.

  4. Please define nested hierarchy for us- and also provide a valid reference to support your definition.

    Thanks.

  5. Hey! I found one! here

    Oh hang on, it’s just someone gibbering on the internet. I think he misses the fact that the subsetting is comprised from a nested group of sets “ancestors-and-all-descendants”, not from separate sets “ancestors” and “descendants”. Each ancestor-and-all-descendants set is embedded within a superior node comprising the immediate ancestor and all its descendants – NOT a set consisting solely of a parent being held to ‘contain’ its descendants.

    And he seems to confuse sexual/HGT trees with the essentially asexual branching of species. The nested hierarchy of Linnaean taxonomy is possible due to coalescence of ancestry of DNA sequence (the real currency of descent) regardless of the different paths through recombinational descent potentially taken by each separate DNA base. Sexual individuals are mosaics, but they can still be grouped hierarchically and nested. Say your family set F is {Mum,Dad,you,sister}. F nests within the set G {grandma 1, grandad 1, grandma 2, grandad 2, {F},{aunts-uncles-and-cousins}} Going up the nodes adds more ancestors and brings in more nested sets of lower nodes – but the whole is still hierarchic and nested. And as we go up, we start to get the same individuals appearing at the highest nodes. With close inbreeding, G may consist of just {grandma 1, grandad 1, {F},{aunts-uncles-and-cousins}}. In reality one would hope that inbreeding wasn’t quite that close, but nonetheless, as we go up the nodes, we do not double ancestors indefinitely, but coalesce upon fewer.

  6. Not wishing to cause argument as I may well be wrong but….

    “They tried to explain the phenomenon with the assumption that every once in a while those normally sexually incompatible species crossed and produced offspring”

    This sentence goes completely against one of the basic rules of biology that I learnt in High School….
    A species is separate from another because it cannot interbreed to produce viable offspring…..
    Surely then either the statement in this report is wrong or the basic fundamental description of a species is wrong!

    And just as a side point….you should never assume because it makes an ass out of you and me…. just saying, that assuming is not a valid argument to base scientific announcements on.

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