All eukaryotes have three essential DNA-dependent RNA polymerase enzymes. These enzymes control gene activity by constructing chains of RNA molecules using DNA genes as templates in a process called transcription. Beyond these three RNA polymerases, known as Pols I, II and III, plants are unique. They have two additional 12-subunit enzymes called Pols IV and V, which maintain genetic stability by silencing transposable elements, viruses and specific genes. A new study shows functionally distinct subtypes Pols IV and V exist in corn, revealing new RNA polymerases with novel functions in all plants.
By characterizing new subtypes of RNA polymerases, this study reveals novel insights into enzymes important for genome stability and gene regulation related to plant development. An understanding of how genome regulation influences biomass production and yield is important for optimized biofuel production and sustainable agriculture to meet the needs of growing populations and combat hunger around the world.
Collaborative researchers from Indiana University, Environmental Molecular Sciences Laboratory (EMSL), Pacific Northwest National Laboratory (PNNL), The University of Arizona, Florida State University, and Monsanto Company identified subunits of Pols IV and V in corn by performing mass spectrometry at EMSL, a Department of Energy national scientific user facility. Surprisingly, proteomic analyses revealed corn Pols IV and V differ from each other only in their largest subunit, which must be key to their different functions. Moreover, there were several differences in the subunit compositions of Pols IV and V in corn compared with Arabidopsis—a small flowering plant that last shared a common ancestor with corn more than 100 million years ago. For example, Arabidopsis Pols IV and V differ from Pol II in four or five of their 12 subunits, respectively, and differ from one another in three subunits. By contrast, corn Pols IV and V differ from Pol II in six subunits.
Researchers also found flexible assembly of different subunit variants produce two alternative forms of Pol IV and three distinct subtypes of Pol V in corn. According to the authors, different subtypes of enzymes may be enriched in different cell types, tissues or organs, where they carry out distinct roles in regulating plant development and gene activity. The findings reveal these intriguing enzymes are continuing to diversify in plants and shed new light on how distinct RNA polymerases have evolved from a single ancestral form of RNA polymerase, as in bacteria and archaea.
Contact: Craig S. Pikaard, Indiana University, firstname.lastname@example.org
Funding: Portions of this research were supported by a National Institutes of Health grant, National Institutes of Health National Center for Research Resources, EMSL, Howard Hughes Medical Institute and Gordon and Betty Moore Foundation.
Publication: Haag JR, B Brower-Toland, EK Krieger, L Sidorenko, CD Nicora, AD Norbeck, A Irsigler, H LaRue, J Brzeski, K McGinnis, S Ivashuta, L Pasa-Tolic, VL Chandler, and CS Pikaard. 2014. "Functional Diversification of Maize RNA Polymerase IV and V Subtypes via Alternative Catalytic Subunits." Cell Reports 9:378-390. doi:10.1016/j.celrep.2014.08.067
- Indiana University
- Howard Hughes Medical Institute
- Monsanto Company
- The University of Arizona
- Florida State University
- National Institutes of Health