Evolución genómica en plantas

De Mendoza CONICET

Plant Genome Evolution


Horizontal gene transfer (HGT), the exchange of genetic material between more or less distantly related, “non-mating” organisms, is widespread in prokaryotes and, to a lesser extent, unicellular eukaryotes. Over the past few years, however, HGT involving multicellular eukaryotes has been increasingly reported. Most well-documented examples of HGT in multicellular eukaryotes come from plant mitochondrial genomes. All but one of the 23 recently discovered cases of plant mitochondrial HGT involve transfer from one flowering plant (angiosperm) to another, often between distantly related angiosperms (e.g., monocots and dicots). Although a number of plant mitochondrial HGT have already been identified based on a modest sampling, no evidence of HGT has been found in land plant chloroplast genomes despite far greater sampling, and only a few cases of nuclear HGT have been described among plants. Therefore, plant mitochondrial DNA (mtDNA) is exceptionally prone to HGT, yet is still relatively poorly studied.

Plant mitochondria genomes are exceptional for several reasons. They are extraordinarily large (200-2400 kb) with large intergenic spacers, accounting for 78-98% of the genome that remain mostly uncharacterized. The presence of repeated sequences facilitate frequent rearrangements and structural changes, which may allow for increased tolerance to acquisition of foreign DNA. HGT in plant mitochondria often results in the presence of two intact copies of a particular mitochondrial gene, one native and one foreign copy. Chimeric genes formed by recombination of native and foreign copies of a mitochondrial gene have also been described. Little is known about the expression and functional implications of these horizontally transferred genes.

Parasitic plants are particularly prone to HGT, given the close interaction with their plant hosts. The frequency and evolutionary implications of these HGT are not clear. We are studying a holoparasitic plant, Lophophytum leandrii, which parasitizes exclusively one host plant, Parapiptadenia rigida. At least one mitochondrial gene has been horizontally acquired from its host. At the moment, we are analyzing the evolution of other mitochondrial genes from the parasite and its host, and whether these genes are expressed or not.

The most frequently documented case of HGT in eukaryotes involves an intron present in the mitochondrial cox1 of flowering plants. This group I intron was originally transferred to angiosperms from a fungal donor and subsequently spread among many diverse angiosperms via hundreds if not thousands of plant-to-plant transfer events. Group I introns often encode site-specific DNA endonucleases and which facilitate intron propagation. The remarkably high frequency of horizontal transfer of the cox1 intron in plants, and the presence of an intact homing endonuclease-like reading frame in almost all plant cox1 introns, predict that the plant cox1 intron encodes an active homing endonuclease, but there is no direct, genetic or biochemical evidence to support this inference.

Main Goals:

  • Determine whether the cox1 intron encodes a functional endonuclease and characterize its homing ability.
  • Investigate the mitochondrial genome in stable cybrid lines from Solanaceae species, including gene content and genomic recombinations.
  • Evaluate the frequency of horizontal gene transfer between parasitic and host plants.
  • Analyze the mitochondrial and plastid genomes of parasitic plants.
  • Examine evolutionary relationships of parasitic plants of the family Balanophoraceae.

To Home Page: Grupo de Evolución Molecular de Plantas or Evolutionary Genomics Lab

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