THE INFLUENCE OF STRIGOLACTONE ON AUXIN TRANSPORT

Our objective was to asses the influence of the new ly described plant hormone strigolactone on the polar auxin transport, that could play a role in a feedback regulation of the homeostasis of auxin and strigolactone. As a model system the roots of Arabi dopsis WT (Columbia), max1 ‐ max4 mutants and PIN1:PIN1:GFP plants were used. The plants were grown on vertical agar plates on control (MS medium) and GR24 (synthetic strigolactone analog) supplemented medium. The root architecture (length of primary root and number of lateral roots ), PIN1-3 gene expression and PIN1 protein localization were determined. The addition of GR24 caused an increase in the leng th of the WT primary root and decreased the number of lateral roots (LR). This could be explain ed by a lower auxin level in the root elongation zo ne and by a delay in formation of auxin maxima needed for lateral root initiation, both effects signalizi ng that GR24 impairs polar auxin transport. The roots of max1 ‐ max4 are known to have higher auxin transport capacity form more lateral roots than WT plants and GR24 decreased the number of LR to WT level. The observed longer primary root of these mu tants and further elongation by GR24 addition could not be satisfactorily explained yet. Real time PCR quantification of PIN1 ‐ 3 gene expression revealed the most pronounced decrease after 2 days of GR24 treatment. There was also observed b y confocal microscopy of PIN1:PIN1:GFP roots a dramatic decrease of expression on the protein leve l. Altogether the results show a modulation of pola r auxin transport capacity by strigolactone on transc riptional or translational level and possibly also by influencing protein stability.