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Hutton Seminar Series: Plant ABCB organic acid transporters - fidelity, polyamory or just multitasking?

Hutton Seminars
10 July 2017, 11am
at James Hutton Institute, New Seminar Room (Dundee) and Macaulay B (Aberdeen)
for scientists, students, researchers and anyone interested
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The B subgroup of ATP Binding Cassette (ABCBs) transporters is ubiquitous across phyla. Although originally associated with efflux of a broad range of hydrophobic substrates in mammalian cancer cells, phylogenetic and physiological evidence suggests that efflux of aliphatic and aromatic organic acids associated with ABCBs in plants is an ancestral function. An additional small anion (Cl-, NO¬3-) channel-like activity has also been associated with these transporters in all systems identified. Association of ABCB isoforms with transport of the aromatic organic acid hormone indole-3-acetic acid (auxin) and dwarfism associated with loss of function in maize and sorghum has given prominence to the function of these transporters. Structural and functional studies suggest the topological and dynamic features underlying ABCB function. In all cases studied to date, exclusion from the outer membrane leaflet and channel-like activities are common to all isoforms, whereas efflux of substrates is regulated by central pore size and conditional substrate uptake is regulated by alterations in transmembrane organization. Although notoriously difficult to characterize in single cell systems, recent structural information and computational analyses make ABCBs a valid target for mutational attempts to modify function.

Mutational studies in the model plant Arabidopsis have been used to analyse ABCB function, but morphological phenotypes of orthologous mutants in monocots suggest differential function. These differences could reflect the multiple substrate specificity associated with mammalian ABC transporters. However, more detailed biochemical and developmental studies suggest functional conservation across plant species. Experimental evidence and observed regulation of ABCB abundance and activity by salts and soil N levels also suggests that secondary anion channel activity might be a more significant function. Experimental results must be evaluated with some discrimination, as experimental use of large excesses of salts and N trigger global processes that are not related to specific ABCB function. These results do suggest that modulation of ABCB function is likely to occur under salt stress conditions associated with controlled irrigation in xeric and sub-xeric soils.

Professor Murphy’s research focusses on the processes that control movement of auxin to regulate programmed and plastic plant development, in particular during responses to changing environmental factors such as light and salinity. The lab also studies the mode of action of other aromatic acids, such as herbicides, that function in plant and fungal growth processes and their potential ecological side effects. This is achieved through a combination of structural biology, biochemistry, cell biology, comparative systems biology, and molecular genetics.

Professor Murphy has a proven track record of engaging with agricultural end users to direct and define his research aims and has established a working relationship with farming advisory groups. He is on the editorial boards of the Journal of Experimental Botany, Plant and Cell Physiology and Frontiers in Plant Science.

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The James Hutton Research Institute is the result of the merger in April 2011 of MLURI and SCRI. This merger formed a new powerhouse for research into food, land use, and climate change.