Though researchers now generally agree that horizontal gene transfer is relatively common among simple organisms like bacteria, they have continued to assume that it remained relatively rare among complex organisms like plants and animals.
“The thinking has been that there is very little horizontal gene transfer among plants and animals except for a few big, ancient events and maybe the occasional transfer of a single gene here or there,” Slot said. “Our discovery suggests that the horizontal transfer of gene clusters may have been a big player not only in the evolution of bacteria but also in more complex organisms.”
Another genome from a single-celled organism has been sequenced. This time it is the green algae, Chlorella. Chlorella are tiny algae that can reproduce quite rapidly. Yet despite the stream-lined nature of the organism, it retains most of the phytohormone biosynthesis pathways necessary to the development and growth of land plants.
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Another interesting feature of the NC64A genome was the presence of homologs of receptors and biosynthetic enzymes of land plant hormones, such as abscisic acid, auxin, and cytokinin. The presence of these homologs does not necessarily imply the existence of plant hormones and their related functions in Chlorella but supports the hypothesis that genes involved in phytohormone biosynthesis and perception were established in ancestral organisms prior to the appearance of land plants.
Not only does this genome add more evidence to the growing plausibility of front-loading, but it also seems to offer a clue that the horizontal transfer of genetic information played a key role in the evolution of one of its key features – it’s unique chitin cell wall.