LawfulBlade Posted September 29, 2011 Posted September 29, 2011 This just came up in another forum, so I wanted to share this article in response. As I'm new here, I wasn't sure whether this was the appropriate room, or if it's ok to tack it on to the previous thread. I'm planning on doing both, and hope that someone will tell me not to do it again, if it's considered to be forum flooding here. The comment I made in a different thread was about the presumptive origin of both chloroplasts and mitochondria: they're both hypothesized to have ultimately been bacteria, or have come from bacteria, back in the day. In other words, they were nested symbiants. As it hasn't connected to my work at all, I've found the idea intriguing, but never bothered to look up any supporting info. And today, suddenly, I found an online article about this exact topic, called "A Bug in a Bug in a Bug". It's a blog post, and should be accessible to all as a result, is a fun read, and it links to the appropriate journal article at the end, if you wish to read the primary literature. Enjoy, and let me know what you think! http://schaechter.asmblog.org/ 1
CharonY Posted September 30, 2011 Posted September 30, 2011 Actually mitochondria and plastids are endosymbionts, and it is not a nested symbiosis (for that the endosymbionts would have to carry other, smaller bacteria themselves). There are a lot of interesting symbiotic relationships around. For instance, Photorhabdus is a bug that is a symbiont to nematodes. The fun bit is that the nematode infects bugs, regurgitates the bacteria, those then kill the host, and both feast on the dead insect. Then, in the next cycle the next generation of nematodes takes Photorhabdus up again and searches for new prey.
LawfulBlade Posted September 30, 2011 Author Posted September 30, 2011 Actually mitochondria and plastids are endosymbionts, and it is not a nested symbiosis (for that the endosymbionts would have to carry other, smaller bacteria themselves). There are a lot of interesting symbiotic relationships around. For instance, Photorhabdus is a bug that is a symbiont to nematodes. The fun bit is that the nematode infects bugs, regurgitates the bacteria, those then kill the host, and both feast on the dead insect. Then, in the next cycle the next generation of nematodes takes Photorhabdus up again and searches for new prey. Are they known to be endosymbionts, then (as opposed to unusual organelles)? Although I never heard anything about the DNA within chloroplasts, I *do* know that the mDNA is totally distinct from the human genome. That said, at the time, it wasn't known that the DNA was definitively of bacterial origin. This easily could have been demonstrated, as I learned about that being a hypothesis a looooooong time ago. In the other thread, the term "nested" wasn't used. Didn't know that it required a third player. Thanks for the correction .
CharonY Posted September 30, 2011 Posted September 30, 2011 Actually it is pretty much established that mitochondria and plastids are of bacterial origin. In addition to the DNA the presence of an additional membrane with bacteria-like lipid components are pretty much strong indicators. The point regarding the DNA is not that it is different from human (how could it?) but rather that the organization and genes are closer to bacterial ones. Thus, they encode (and hence, express) ribosomes that are bacterial in structure. However, the timing is not quite clear. I.e. whether the eukaryotic cell arose first and then internalized the bacteria, or whether the original host was a prokaryote itself.
phasevelocity Posted November 16, 2011 Posted November 16, 2011 Are they known to be endosymbionts, then (as opposed to unusual organelles)? Although I never heard anything about the DNA within chloroplasts, I *do* know that the mDNA is totally distinct from the human genome. That said, at the time, it wasn't known that the DNA was definitively of bacterial origin. This easily could have been demonstrated, as I learned about that being a hypothesis a looooooong time ago. In the other thread, the term "nested" wasn't used. Didn't know that it required a third player. Thanks for the correction . The mRNA (it is RNA not DNA) is distinct form nuclear DNA because evolution has weeded out most of the access redundant mRNA and has even moved most of the mRNA that does not need to be at the mitochondrial location to the nucleus. So most genes coding for mitochondrial proteins are now in the nucleus. Chloroplast RNA is called plastome.
CharonY Posted November 16, 2011 Posted November 16, 2011 1) Plastids possess their own DNA (you may be confusing coding regions with mRNA) 2) likewise the plastome refers to the totality of the genetic material in plastids (i.e. total DNA). The totality of its transcripts would be the transcriptome (I do not think that someone invented a specific term for the plastid transcriptome).
phasevelocity Posted November 17, 2011 Posted November 17, 2011 Yes you are correct. I was sloppy. The plastome is referring to DNA. Here is a reference: http://www.google.nl/url?sa=t&rct=j&q=plastome%20dna&source=web&cd=13&ved=0CCQQFjACOAo&url=http%3A%2F%2Fjcs.biologists.org%2Fcontent%2F104%2F1%2F1.full.pdf&ei=CLTETrSeOtOBhQfwxvnjDQ&usg=AFQjCNG4xFL3d9fXyfkqWNQocSa2Nj2_bA&cad=rja
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