Genes might come from source other than mother and father

Mother Nature is proving that the transfer of genes is more complicated than scientists thought.\nBelieved to be extremely unlikely among multi-cellular organisms, gene swapping appears to occur widely among unrelated species of plants, according to researchers led by IU biology professor Jeff Palmer.\nIn the most recent issue of the journal Nature, Palmer and colleagues reported five out of more than 100 genes sequenced from flowering plants were transferred from unrelated species. Their findings hint that horizontal gene transfer also might occur among other unrelated complex organisms, including animals. \nThe findings are surprising news to biologists who believed gene inheritance in multicellular organisms could only occur vertically, by transmission from parent to offspring. \n"This work will certainly force genomic researchers to rethink the evolutionary forces affecting genome structure and definitely widens our horizon on the biological potential of nature," said James R. Brown of the Bioinformatics Division of GlaxoSmithKline, a pharmaceutical company.\nScientists have been studying this kind of gene swapping among bacteria and other single-celled organisms for many years. The incorporated genes are often important for bacteria, giving them additional traits, such as resistance to antibiotics.\nThe importance of these gene transfers for plants is part of a continuing study, but it seems clear that at least some of these genes take an active role in plants. Palmer's team has shown that two out of the five discovered genes are processed within the cell. Surprisingly, one of these active genes from bloodroot is chimeric, meaning that a portion was passed faithfully from parent to offspring and another portion acquired by a different mechanism from a different species.\nThe cases that Palmer and his coworkers have found are probably only a few among many cases of gene transfer in plants.\n"In aggregate, I'm certain the five cases we've documented now represent the tip of an iceberg," Palmer said. "There's probably thousands of cases that occurred during the flowering plant evolution."\nBut each case of horizontal gene transfer is relatively rare because these potentially thousands of incidents have occurred over tens of millions of years. Therefore, discovering exactly how these transfers occurred might be incredibly difficult, or there might not be a consistent mechanism. \n"What we're doing here is basically a kind of molecular archaeology," Palmer said. "We're sifting through the genetic debris of millions of years of evolution looking for clues."\nAnd because these events might occur once in a 100,000-year period, horizontal gene transfer from genetically modified crops should not represent a threat to other unmodified plant species, said Palmer and postdoctoral associate Ulfar Bergthorsson, who is working on the project.\nIn a world where scientists have sequenced the genome for many species of plants and animals, the issue of horizontal transfer complicates the interpretation of that data. With the assumption that all genetic material was passed relatively faithfully from parent to offspring, scientists have mapped trees of relationship based on genetic data. \nIn cases of horizontal transfer, largely unrelated organisms show unexpected relationships to organisms far outside their branch of the family tree. Bergthorsson said he sees a new interpretation of the tree of life as the most significant implication of the research.\n"I think the main message from this work is that we have to start taking the process of lateral transfer seriously," he said. "We always tried to interpret everything in terms of things falling down in a tree-like fashion, but the tree of life may not be so much a tree but more like a web, perhaps, with connecting branches"