Nihal Dharmasiri, Ph.D.
Plant Physiology (BIO 3465)
Principles of Developmental Biology (BIO 3490)
Seminar in Molecular and Cell Biology (BIO 7102)
Molecular Biology of the Cell (BIO 7103D)
Molecular Genetics of Plant Development (BIO 7103F)
Plant growth and development is regulated by both endogenous and environmental factors. Several plant hormones function as key endogenous regulators of plant development. Functions of these hormones are subjected to environmental regulation resulting in the final plant form that is shaped by both these factors. Our long-term goal is to understand the molecular mechanisms underlying interactions among plant development, hormones and environmental factors, and to use such knowledge to improve productivity of plants, whether they are crop plants or biofuel feedstocks.
Our lab currently focuses on how the plant hormone auxin controls plant growth and development in conjunction with environmental factors. We use the model plant Arabidopsis thaliana in our research. Auxin controls many aspects of plant growth, primarily by regulating cell division, cell expansion and cell differentiation. At the molecular level auxin controls these processes by regulating the expression of many genes. Auxin regulates these genes by the degradation of a group of transcriptional repressors known as Aux/IAA proteins. These repressors are degraded through ubiquitin-proteasome pathway involving SCFTIR1/AFBs. TIR1 and AFBs belong to a group of proteins known as F-box proteins. TIR1/AFBs along with Aux/IAA proteins function as co-receptors for auxin.
While indoleacetic acid (IAA) is the major form of natural auxin found in plants, there are many synthetic chemicals with auxinic activity such as 2,4-D, 1-NAA and picloram. Our work, along with others, shows that picloram functions differently than other commonly know auxinic compounds. We have recently isolated a number of Arabidopsis mutants that are resistant to picloram. Currently, we are in the process of cloning and characterizing mutant genes and elucidating their functions in plant auxin response. Recent studies from several labs indicate that plant auxin response is subjected to regulation by environmental stresses. In fact the expression of some auxin related genes is modulated by environmental stresses.We are interested in finding how these genes bridge environmental cues to plant auxin response. We use a combination of genetic, molecular, biochemical and microscopy techniques to understand how these genes function in auxin signaling pathway.
Auxinic herbicides have been used for a long time to selectively control broad leaf weeds in crops. However, these selective herbicides cannot be used in many dicot crops such as cotton, potato, soybean and tomato. Identification of auxin resistant mutant genes also gives the opportunity to use these mutant genes to generate herbicide resistance. We are currently investigating the possibility of using some auxin resistant mutant genes for generating herbicide resistant crop plants.
Jayaweera, T, Siriwardana, C, Dharmasiri, S, Quint, M, Gray, WM, Dharmasiri, N (2014) Alternative splicing of Arabidopsis IBR5 pre-mRNA generates two IBR5 isoforms with distinct and overlapping functions. PLOS ONE 9, Article Number: e102301
Dharmasiri, S, Harrington, HM, Dharmasiri, N (2010) Heat shock modulates phosphorylation status and activity of nucleoside diphosphate kinase in cultured sugarcane cells. Plant Cell Reports 29:1305-1314.
Savaldi-Goldstein S, Baiga TJ, Pojer F, Dabi T, Butterfield C, Parry G, Santner A, Dharmasiri N, Tao Y, Estelle M, Noel JP, Chory J (2008) New auxin analogs with growth-promoting effects in intact plants reveal a chemical strategy to improve hormone delivery. Proc Natl Acad Sci USA 105: 15190-15195.
Dharmasiri, N, Dharmasiri, S, Weijers, D, Karunarathne, N, Jurgens, G, Estelle, M (2007) AXL1 and AXR1 have redundant functions in RUB conjugation and growth and development in Arabidopsis. Plant J. 52:114-123.
Dharmasiri, S, Swarup, R, Mockaitis, K, Dharmasiri, N, Singh, SK, Kowalchyk, M, Marchant, A, Sandberg, G, Bennett, M, Estelle, M (2006) AXR4 is required for asymmetric localization of the auxin influx facilitator AUX1. Science 312: 1218-1220.
Navarro, L, Dunoyer, P, Jay, F, Arnold, B, Dharmasiri, N, Estelle, M, Voinnet, O, Jones, JDG (2006) A plant miRNA contributes to antibacterial resistance by repressing Auxin signaling. Science 312: 436-439.
Dharmasiri, N, Dharmasiri, S, Estelle, M (2005) The F-box protein TIR1 is an auxin receptor. Nature 435: 441- 445.
Please see faculty member’s CV or website for a complete list of publications and additional information.