Conserved auxin signalling synergism through the canonical and ETT-mediated pathways promotes gynoecium development in members of theBrassicaceae

Abstract

AbstractGynoecium polarity establishment is regulated by auxin, a phytohormone whose signal is transduced through several pathways. The relationship between the ETT and canonical TIR1/AFB pathways, and their relevance for carpel development beyondArabidopsis thaliana, have not been investigated. The data presented here show that the expression patterns of canonical and ETT-mediated signalling components, and phenotypes of higher order mutants are shared betweenArabidopsisandCapsella rubella.tir1 afb2 ettmutants partially phenocopyett arf4double mutants, suggesting a role for AUXIN RESPONSE FACTOR 4 (ARF4) in the integration of canonical and ETT-mediated signalling. Comparative transcriptomics revealed that the auxin-independent mis-regulation ofYABBYgenes correlate with patterning defects observed inArabidopsis ett arf4mutants. Together, the data presented suggest conserved synergism between canonical and ETT-mediated pathways in gynoecium polarity establishment in theBrassicaceae. Finally, the data suggest that ETT/ARF4 function to prevent the auxin-induced expression of a range of targets inArabidopsis, consistent with activator-repressor ARF antagonism, and implying that the maintenance of auxin insensitivity by repressive ARFs is important for a range of biological processes.Summary StatementHere the relationship between canonical and ETT-mediated auxin signalling machineries is investigated inArabidopsisandCapsellarevealing conserved synergism between these two pathways inBrassicaceaewith distinct fruit shapes.