Tuesday, June 1, 2010

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FIRST CASE OF ANIMAL SYMBIOSIS summarizing CAROTENE



According to researchers at the University of Arizona, the insects known as
aphids are able to synthesize their own essential nutrients called carotenoids
.
Until now, scientists thought that the only way which animals were able to obtain these compounds from the diet.
Carotenoids are molecules essential for vision, skin, bone growth and other fundamental physiological functions. The beta-carotene, the pigment that makes carrots orange, is the main molecule for the "construction" of vitamin A. "Once you start
how widespread the carotenoids, you realize that are everywhere in life," said Moran, a professor of ecology and evolutionary biology. " The yellow color of egg yolks, the pink shrimp and salmon, pink flamingos, tomatoes, carrots, peppers, Mexican poppies, marigolds, etc. ..
. "
Moran and his co-author Tyler Jarvik have speculated how the aphids have acquired the ability to synthesize carotenoids.
" probably during the evolution of aphids have been cases where a fungal gene has entered the DNA has been copied and dell'afide , "explained Moran. "
Although gene transfer between microorganisms is a common phenomenon, is the first time that there is a trace of a fungal gene in the genome of an animal
."

"Animals have many needs that reflect a loss of ancestral genes, which is why we need to take vitamins and amino acids in the diet , "explained Moran. "
So far it was believed that there was simply no way to regain this lost capacity. But in the case of aphids seems that this hypothesis is disproved."
"Probably this will be an extraordinary rare case. But so far in genomic studies, a single initial case, which usually turns out to be just one example of something more widespread
. "
. A happy accident in the lab more recent sequencing of the genome of the pea aphid made the discovery as possible, said Moran.

Aphids of pea, known to scientists as
Acyrthosiphon pisum, are red or verdi.Inoltre reproduce by cloning - the mothers were giving birth to daughters that are genetically identical. So when an aphid in the laboratory strain red 5A Moran began to give birth to offspring with yellow-green, Moran and his colleagues knew they were watching the results of a mutation. Aphids live in symbiosis with certain bacteria that are passed from mother to daughter, providing a crucial part of feeding insects. From studies over several decades, it was known that the three major species of symbiotic bacteria do not produce carotenoids and do not get them from the diet.

Moran, who studied the system of pea aphid-bacteria for decades, he already knew the three main species of symbiotic bacteria are unable to produce carotenoids, they get them from the diet.
Aphids feed by sucking the phloem sap from plants, but the phloem sap is low in carotenoid. Furthermore, carotenoids found in the aphids were different from those usually found in plants.

At the end of 2009, after the complete DNA sequence of the pea dell'afide researchers have begun to seek gene responsible for the synthesis of carotenoids.
All organisms use the same pathway to synthesize carotenoids, "
this has made the search for genes for carotenoid simple

Fortunately for Moran, researchers have sequenced the genome of dell'afide have used the DNA of the pea aphid color red, which have an extra copy of the carotenoid gene, making it easier to find what the color red.
Therefore, it remained to be seen whether the genes derived from the DNA of pea dell'afide or uncommon symbiotic bacteria or fungal contamination in the sample.
In the laboratory, and Jarvik Moran noted that by eliminating the symbiotic bacteria from a strain of aphids did not change the color of the offspring, or the symbiotic bacteria have not been the source of the color red. Moreover, tracing the lineages of aphids strains of red, green and yellow has been shown that the colors had a pattern of Mendelian inheritance, indicating that the DNA coding for the red part of the DNA 's aphid.
This mode of transmission in the form of another research team suggested that both the colors found in nature because the green aphids are more susceptible to parasitic wasps, aphids and red are more susceptible to predators such as lady-bird beetles.
The last piece of the puzzle was to try to understand from where the genes. The particular sequence of DNA coding for the carotenoid nelll'afide differed from bacterial genes for carotenoid and corresponded to those of some fungi.
Moran said that a long-term association between aphids and fungi may have made possible the possible transfer of a gene.
The discovery shows "
the interplay between organisms and their genomes over time and their fusion in different ways."
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