In the late 19th century Gregor Mendel used peas to show that one copy of a gene (allele) is inherited from the mother and one from the father. In the progeny, the inherited genes are expressed at the right time and in the right place, but until recently, it was thought that although gene products could be modified during the life of the organism, the genes themselves were unchanged, except for random mutation.
Now it appears that one copy of some genes can alter the expression of the other copy, and those changes are passed down to the next generation. These epigenetic alterations, called paramutations may be important in introducing changes when plants and other organisms are environmentally stressed. The exact mechanisms of how genes talk to other genes and change their behavior are being investigated, and recent results suggest that these processes could be important in engineering plants responsive to a variety of environmental conditions.
Dr. Vicki Chandler and her colleagues have studied paramutations in maize and other plants and have identified some of the genes and mechanisms that operate in this epigenetic process. Dr. Chandler, of the Department of Plant Sciences at the University of Arizona, Tucson, will be presenting this work at a symposium on Maize Biology at the annual meeting of the American Society of Plant Biologists in Mérida, Mexico (June 28, 9:10 AM).
The sequencing of genes, proteins, and, ultimately, whole genomes has revealed that genomes are not simply strings of genes, but rather complex, communicating, and interacting regions of information that could be compared to DNA computers controlling growth, development, and metabolism in each organism. The physical architecture of the genome is also highly complex. The nucleus, where the genome resides, is not full of strings of DNA like a pot of spaghetti. Rather, the strands of DNA are wrapped around proteins called histones and the whole is organized into an elegant and highly controlled structure called chromatin. When it is time for genes to be expressed, a section of chromatin is unwound and the DNA for that particular gene is made available to the machinery that transcribes DNA to RNA. Once the process is finished, the DNA is neatly folded back into the chromatin structure until needed again. Different parts of the genome can interact by direct contact or through intermediaries that can be proteins or RNA sequences. The exact mechanisms of how paramutagenic alleles communicate with their homologous partners are still unknown, but the work of Chandler and others suggests that both direct contact of homologous regions and changes induced by intermediary RNA molecules may be involved.
Peas also played an important role in the discovery of paramutations, as the first mutants of this type were observed in peas in 1915. Then, in the 1950s, Alexander Brink identified these types of mutations as interactions between alleles. He recognized that these interactions resulted in heritable changes to the expression of those genes. Since then, paramutations have been found in humans and other animals, as well as other plant species including tomato, tobacco, petunia, and maize. In animals, paramutations may be important in mediating the occurrence of diseases like diabetes. Chandler and her co-workers have been investigating paramutations in maize at the b1 gene, which regulates the distribution of the purple pigment anthocyanin in plant tissues.
At the b1 locus, the paramutagenic allele, which causes light or stippled pigmentation arises spontaneously from the wild-type allele, which causes dark purple pigmentation. If a plant with the paramutagenic allele is crossed with a wild-type allele, the progeny get both alleles. However, the paramutagenic allele silences the wild-type allele and produces a plant with stippled rather than purple pigmentation. The silent state is then passed on in subsequent crosses.
Several different components may be involved in paramutation, although they may differ among species. One important player is an array of repeated non-coding DNA sequences that lies upstream of the gene sequence of the paramutagenic allele. Seven of these tandem repeats are required for b1 paramutation. If only three tandem repeats are present, there is only partial paramutagenic activity. One possibility is that these tandem repeats are involved in direct interactions of chromatin regions, which results in paramutation changes. However, RNA also appears to be part of the process. The gene mediator of paramutation1 (mop1), an RNA dependent RNA polymerase is absolutely required for paramutation silencing at the b1 locus as well as for several other maize genes. In Arabidopsis, this RNA polymerase is associated with the production of small, interfering RNAs (siRNA) that function in gene silencing in other contexts. The siRNA could thus act as an intermediary molecule, being sent to silence the homologous allele. A third component is the placement of methyl groups on the control sequence (promoter) of the wild-type gene. Gene methylation has been known for some time as a cell defense mechanism for silencing foreign DNA but is also functional in other cellular processes. In several species, such methylation is also directed by RNA molecules. None of these processes is likely to be sufficient by themselves to effect paramutation, but rather all of them may interact, although to varying degrees in different species.
The molecular components of paramutation probably arose as cell defense mechanisms against viral or bacterial DNA. They have evolved to serve the needs of plants that grow in complex and changing environments from which they cannot escape, but to which they may be able to adapt through mechanisms like paramutation. Indeed, two instances of paramutation are known to be influenced by temperature. This work has implications for engineering crops that may be able to adapt to higher temperatures or drought conditions, as well as for applications in human and veterinary medicine.
Vicki Chandler | EurekAlert!
Link Discovered between Immune System, Brain Structure and Memory
26.04.2017 | Universität Basel
Researchers develop eco-friendly, 4-in-1 catalyst
25.04.2017 | Brown University
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
26.04.2017 | Materials Sciences
26.04.2017 | Agricultural and Forestry Science
26.04.2017 | Physics and Astronomy