Navigation Links
Genome communication

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 Mrida, 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.


Contact: Vicki Chandler
American Society of Plant Biologists

Related biology news :

1. Unravelling new complexity in the genome
2. Conquest of land began in shark genome
3. One species entire genome discovered inside anothers
4. Genome study shines light on genetic link to height
5. First individual genome sequence published
6. Ultraconserved elements in the genome: Are they indispensable?
7. $10 million gift to support cutting-edge epigenome center at USC
8. Fungus genome yielding answers to protect grains, people and animals
9. Which came first, the chicken genome or the egg genome?
10. Researchers expand efforts to explore functional landscape of the human genome
11. Genome update defines landscape of breast and colon cancers
Post Your Comments:
(Date:5/16/2016)... --  EyeLock LLC , a market leader of iris-based ... IoT Center of Excellence in Austin, Texas ... embedded iris biometric applications. EyeLock,s iris authentication ... with unmatched biometric accuracy, making it the most proven ... platform uses video technology to deliver a fast and ...
(Date:5/9/2016)... Elevay is currently known as ... for high net worth professionals seeking travel for work ... world, there is still no substitute for a face-to-face ... your deal with a firm handshake. This is why ... of citizenship via investment programs like those offered by ...
(Date:4/28/2016)... India , April 28, 2016 ... Infosys (NYSE: INFY ), and Samsung SDS, a ... that will provide end customers with a more secure, ... services.      (Logo: ) , ... services, but it also plays a fundamental part in enabling ...
Breaking Biology News(10 mins):
(Date:6/23/2016)...  The Biodesign Challenge (BDC), a university competition that ... living systems and biotechnology, announced its winning teams at ... New York City . The teams, ... at MoMA,s Celeste Bartos Theater during the daylong summit. ... curator of architecture and design, and Suzanne Lee ...
(Date:6/23/2016)... ... ... STACS DNA Inc., the sample tracking software company, today announced that Dr. Hays ... DNA as a Field Application Specialist. , “I am thrilled that Dr. Young ... DNA. “In further expanding our capacity as a scientific integrator, Hays brings a wealth ...
(Date:6/23/2016)... 23, 2016  Blueprint Bio, a company dedicated to ... medical community, has closed its Series A funding round, ... "We have received a commitment from Forentis ... need to meet our current goals," stated Matthew ... runway to complete validation on the current projects in ...
(Date:6/23/2016)... ... June 23, 2016 , ... ClinCapture, the only free validated ... will showcase its product’s latest features from June 26 to June 30, 2016 ... on Disrupting Clinical Trials in The Cloud during the conference. DIA (Drug ...
Breaking Biology Technology: