A FLOWERING shrub found only on the mountainside of New Caledonia, a tiny island nearÃ”Ã‡ÃªAustralia, offers clue to evolution of flowering plants. The plant, Amborella trichopoda, is considered to be the lone species of one of the two evolutionary lineages of flowering plants. The other lineage comprises more than 300,000 species. Since Amborella is the direct descendent, scientists had long believed that understanding its genome would help understand the evolutionary process of flowering plants, which include most food crops.
Researchers from Penn State University, the University at Buffalo, the University of Florida, the University of Georgia and the University of California-Riverside in the US have recently sequenced the complete genetic material (present in both nucleus and mitochondria) of Amborella. They have found that the ancestor of all flowering plants evolved following a genome doubling event that occurred some 200 million years before the lineage diversification. While some of the duplicated genes were lost over time, others took on new functions such as controlling development of floral organs.
Amborella seems to have acquired some unique characteristics since it branched off. Unlike in other flowering plants, DNA sequences that can change locations or multiply within the genome seem to have stabilised in Amborella, affecting the expression of genes and resulting in slowed rate of evolution. The researchers also found its mitochondrial genome containing genes from a number of other plant species, including three green algae and one moss. This is believed to be the largest example of horizontal gene transfer—the acquisition of foreign genes from other species—in any organism. It could be that these organisms lived in close association with Amborella millions of years ago, the researchers note in two papers published in the December 20 issue of Science.
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