Auxin is an essential plant hormone that regulates diverse processes, such as cell division and expansion, embryogenesis, meristem formation, root and leaf patterning, tropism, and reproduction. Extensive molecular studies have identified a large set of auxin inducible genes and the auxin responsive cis-elements and the relevant trans-acting factors. Genetic approaches have led to the isolation of genes involved in auxin responses and transport and the unraveling of protein degradation control in auxin signaling.

Our lab has been interested in understanding the molecular and biochemical mechanisms underlying the auxin signal transduction pathway that control nuclear gene transcription and plant morphogenesis. We have taken novel molecular genetic and genomic approaches to identify regulatory genes important for auxin-inducible transcription and morphogenesis by using tobacco and Arabidopsis as model systems. We have established efficient transient and stable transformation systems that will allow the identification of genes that can perturb (both gain-of-function and loss-of-function) various steps of the auxin- dependent transcription and morphogenesis, including cell proliferation, elongation, and differentiation. These expression cloning and functional genomic analysis methods could facilitate the identification of genes involved in cell shape, growth polarity, cell division, cell death, organogenesis, embryogenesis and gene expression. The use of the jellyfish green-fluorescent protein (GFP) provides an excellent visual marker to follow auxin responses in living cells. The experimental design can overcome lethality and functional redundancy, which may limit the isolation of more specific mutants important for the elucidation of the auxin signal transduction pathway.

Based on the control of early response gene transcription, we have explored the functions of mitogen activated protein kinase (MAPK) signaling cascades in the regulation of auxin responses. We have discovered both positive and negative roles of MAPK cascades in auxin signaling. The future goals are to define the specific roles of each molecular component and their upstream regulators and downstream targets. In addition, our studies have revealed surprising connections between auxin and stress signaling as well as auxin and sugar signaling in plants. The identification of molecular links connecting auxin and sugar, stress or cytokinin signaling networks will reveal a complex but more realistic view of regulatory circuits in plant cells. The studies have provided novel approaches to manipulate plant life span, seed development, and vegetative and reproductive growth for the improvement of crop yield.