Mechanism of auxin transport
Plant hormone auxin is a key regulator of many developmental processes in plants. It plays a major role in control of temporal and spatial aspects of plant growth and, as such, it co-ordinates plant development. In contrast to other plant growth regulators (plant hormones), in some tissues auxin molecules are transported to long distances through plant body and their transport is strictly directional (polar). Mechanism of the polar auxin transport is based on physical-chemical properties of auxin molecules and on their molecular forms inside and outside cells. It is a very complex and dynamic process with many levels of regulation.
Effect of NPA on auxin transport in tobacco BY-2 cells.
Our laboratory focuses on the molecular mechanism of polar auxin transport and on the ways of its regulation. Using in vitro cultured plant cells (cell suspensions) adapted for direct measurements of auxin flow through cells (Petrášek a Zažímalová, in Biotechnology in Agriculture and Forestry 2006) we have revealed the involvement of cellular auxin efflux in the establishment of polarity of cell division (Petrášek et al., Planta 2002). We have described the response of cytoskeletal structures and endomembranes to the inhibition of polar auxin transport and quantitatively characterized the action of some polar auxin transport inhibitors (NPA and BFA, Petrášek et al., Plant Physiol. 2003). We have also contributed to the characterization of effects of some other inhibitors – TIBA or PBA (Dhonukshe et al., PNAS 2008).
We have participated on the discovery of inhibitory action of auxin on constitutive cycling of proteins, including auxin efflux carriers from PIN protein family (Paciorek et al., Nature 2005). Then we have transformed tobacco cell culture with Arabidopsis PIN genes and determined an array of kinetic parameters of auxin flow in these cell lines. Results obtained led to the conclusion that PIN proteins catalyze directly and with high specificity the transport of auxins from cells to intercellular space and they play a rate-limiting role in auxin flow (Petrášek et al., Science 2006).
We have taken part on characterization of molecular interaction between auxin transporters of PIN- and MDR/PGP/ABCB-type (Mravec et al., Development 2008). On the research of polar auxin transport we collaborate with VIB Department of Plant Systems Biology, Ghent University, Belgium (Prof. Jiří Friml, Dr. Eva Benková and co-workers).
In collaboration with the Laboratory of Molecular Plant Physiology of Faculty of Science of Masaryk University, Brno (Dr. Jan Hejátko and co-workers) and with Dr. Benková’s group in VIB, Ghent we are involved in analysis of interactions between cytokinins and auxins in organogenesis de novo, in particular on the level of regulation of transporters taking part in formation of auxin maxima via polar auxin transport (Pernisová et al., PNAS 2009; Růžička et al., PNAS 2009, respectively).
We have isolated and characterized the gene PaLAX1 from Prunus avium (Hoyerová et al., Plant Physiol. 2008) and we study properties of the corresponding protein.
At present we are interested also on various levels and types of regulation of activity of PIN proteins (Zažímalová et al., Cell. Mol. Life Sci. 2007), we continue to characterize properties of other auxin carriers from AUX1/LAX, PIN and MDR/PGP/ABCB families, and we try to construct a mathematical model of auxin flow through plant cells.