Auxin can act independently of CRC, LUG, SEU, SPT and STY1 in style development but not apical-basal patterning of the Arabidopsis gynoecium.

Patterning of the Arabidopsis thaliana gynoecium is dependent on the localization and concentration of the plant hormone auxin and it has been previously reported that STYLISH1 (STY1) activates transcription of the auxin biosynthesis gene YUCCA4 (YUC4) and affects gynoecium development. Here, the relationship between auxin, STY1 and other regulators of gynoecium development was examined. Exogenous auxin in droplets of lanolin paste were applied to young gynoecia; auxin biosynthesis rate was measured and STY1 overexpression or chemically mediated polar auxin transport (PAT) inhibition were induced in various mutants. The style phenotype of sty1-1sty2-1 mutants was restored by exogenous application of auxin, and STY1 over-activation resulted in an elevated auxin biosynthesis rate. Both over-activation of STY1 and inhibition of PAT restored the stylar defects of several unrelated mutants, but with regard to gynoecium apical-basal patterning the mutants responded differently to inhibition of PAT. These results suggest that reduced auxin concentrations cause the sty1-1 sty2-1 phenotype, that STY1 induces auxin biosynthesis, that elevated apical auxin concentrations can compensate for the loss of several style-promoting factors, and that auxin may act downstream of, or in parallel with these during style development but is dependent on their action in apical-basal patterning.

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