9. Organelle genomes Flashcards
What are the main organellar genomes in eukaryotes?
Nuclear genome
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Organellar genomes:
- mitochondrial -mtDNA
- plastid - chloroplast - spDNA
- secondary plastid - apicoplast
How could a phylogenetic tree be consutructed for different species using genomics?
Choose common genes - comapre their sequence similarity - assign relationships - group
What is mitochondrial origin in eukaryotes?
Mitochindria emerged from endosymbiosis: proto-eukaryote engulfed a bacterium - likely ancestor - α-proteobacterium - ex: Rickettsia
Why do current day mitochondria and chloroplasts have less genomes than their ancestor bacteria which were engulfed by proto-eukarya?
Because of gene loss - only 1-2% genes retained because:
- if same protein produced by host - no need for those genes - lost in adaptation
- some genes moved form mt, cp genomes into nuclear genomes - gene transfer
Do mt genomes vary a lot between species?
Yes, some still have large coding / non-coding regions - human mtDNA very small - majority were transferred to nuclear genome or lost
What is the content of human mt genome?
Human mt genome:
- protein coding genes
- rRNA genes
- tRNA genes
-> needed proteins also produced by nuclear genome
Overall human mt genome rather small - genes lost / transferred to nuclear genome + little non-coding DNA
What is the current day eukaryote which is likely to have the most unchanged, original mt genome?
Reclinomonas americana most likely has least changed mt genome in comparison to the mt ancestor bacterium - most bacteria-like mtDNA genome
What is the current day bacterium which resembles the original mt ancestro bacterium the most?
Rickettsia prowazekii - α-proteobacterium - closest to mitochondria - in comparison genomes even have some retaiend synteny
What is an example gene which is likely to have been transferred from mtDNA into nuclear DNA?
cpn60 chaperonin - likely to have undergone gene transfer from mtDNA into nuclear genome in eukaryotes
Explain what are amitochondrial eukaryotes and how they survive
Amitochondrial eukaryotes - which have lost mt - genes needed for cellular respiration transferred to nuclear genomes
Ex: Parabasalids, Diplomonads, Microsporidia
What are Microsporidia?
Microsporidia - amitochondrial eukaryotes - lost their mt in evolution because they are rather late diverging species from eukaryotes in phylogenetic tree - definitely had mt at some point
Did amitochondrial eukaryotes never get a mt or they lost it?
Amitochondrial eukaryotes lost their mt by transferring mt genes into nuclear genome - all eukaryotes descended from an ancestor with mt
What is the origin of plastid genomes?
Like mt - plastids evolved through endosymbiosis of a bacterium
Cyanobacteria (blue green algae) - most closely related to a chloroplast - most similar ancestor-like current day bacterium
How do cpDNA genome size varies between species?
What is an apicoplast?
Apicoplast - a plastid like chloroplast but non-photosynthetic
- responsible for fatty acid synthesis, iron-sulphur cluster synthesis
- apicoplast - organelle - surrounded by 4 membranes - came from secondary endosymbiosis
Apicoplasts common in pathogens - ex Toxoplasma
Describe what is apicoplast genome like
Apicoplast genome:
- circular
- genes for fatty acid synthesis, iron-sulphur cluster synthesis
- apicoplast - organelle - surrounded by 4 membranes - came from secondary endosymbiosis
Explain apicoplast endosymbiosis
Apicoplast emerged form secondary endosymbiosis - double endosymbiosis fo a cyanobacterium - 4 membranes in the organelle
Secondary endosymbiosis increases number of separate genomes present in a cell - ex: 4 genomes in a single Cryptomonads cell
How does the rate of evolution in organellar genomes vary in comparison to nuclear genome?
In mammals mtDNA x10 faster evolution rate than in nuclear genome - smaller genome + more replicated -> more accummulation
In plants mtDNA x12 and cpDNA x4 evolution rate slower than in nuclear - ???
Different organellar genome evolution rates than nuclear rates because breplciation events are separate
What is the inheritance pattern of mtDNA and cpDNA?
mtDNA and cpDNA inherited uniparentally - mostly maternally but depedns on plant reproduction - some have paternal origin
Lecture summary
