Massive mitochondrial gene transfer to the nucleus occurred very early during eukaryotic evolution following endosymbiosis, and is still ongoing in plants. Tracking recent gene transfer events can give us insight into the evolutionary processes by which a transferred gene becomes functional in the nucleus and how its protein gets targeted back into the mitochondrion, where it is needed. Rps19 and rpl2 are two such ribosomal protein genes that are known to have been transferred to the nucleus, many times independently during flowering plant evolution. My research project focusses on determining the status and expression of rps19 and rpl2 in the mitochondrion and nucleus of selected grasses and in particular brome (close relative to agronomically important crops such as wheat, rye and barley). My results at the level of DNA and RNA (PCR and RT-PCR, respectively) show that the mitochondrial brome rpl2 copy is a pseudogene while its functional gene is in the nucleus. The brome mitochondrial genome has a copy of rps19 which is transcribed and C-U edited. Surprisingly, the brome nuclear genome also has functional copies of rps19.The targeting sequence for the nuclear rps19 gene was acquired from duplication of mitochondrial targeting heat shock protein (hsp70) presequence. Comparative analysis strongly suggests that a functional rps19 gene was transferred to the nucleus before rice and maize lineages split and now that brome rps19 has been found to be present in both compartments, this implies a transition stage of about 60 million years. Oats was found to have a functional rps19 copy in the nucleus and has a novel presequence due to lineage specific rearrangements and exon shuffling. Functional paralogous copies were found in wheat, and maize while barley lost one of the copy. Thus, following transfer, duplication of rps19 gene must have occurred in the ancestor of barley and wheat clade. Maize might have had a recent duplication or gene conversion events along its lineage as its paralogous copies are very similar to each other. More information is needed to determine if this duplication event extends to wheat-brome, wheat-oats or even before rice and maize split. Barley was also found to have a recent independent DNA mediated transfer in addition to the common transfer, as it possesses an unedited nuc-mt rps19 in its nuclear genome. This suggests that barley must also have had a transition stage for ~60MY and lost its mitochondrial copy very recently.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/32268 |
| Date | January 2015 |
| Creators | Atluri, Sruthi |
| Contributors | Bonen, Linda |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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