# Conserved roles of ETT and ARF4 in gynoecium development in Brassicaceae with distinct fruit shapes

## TL;DR

This study explores how ETT and ARF4 work together in plant development across Brassicaceae species with different fruit shapes.

## Contribution

The paper reveals conserved synergism between ETT/ARF4 and canonical auxin pathways in gynoecium development.

## Key findings

- ETT and ARF4 have distinct and overlapping targets in the Arabidopsis gynoecium.
- Mutant analysis shows conserved synergism between ETT/ARF4 and canonical pathways in Brassicaceae.
- ARF4 may integrate these pathways in species with distinct fruit shapes.

## Abstract

Gynoecium patterning is dependent on the dynamic distribution of auxin, the signalling of which is transduced through several distinct pathways. ETTIN (ETT)-mediated signalling occurs independently of the canonical auxin pathway, and ETT shares partial redundancy with Auxin Response Factor 4 (ARF4) in the gynoecium. ETT and ARF4 were previously hypothesized to translate auxin gradients into patterns of tissue polarity alongside other ARFs. As ARF repressors, ETT/ARF were assumed to antagonistically regulate targets shared with ARF activators of the canonical pathway. Here, comparative transcriptomics identified the distinct and overlapping targets of ETT/ARF4 in the Arabidopsis gynoecium. However, ETT/ARF4 targets with known roles in gynoecium development did not conform to models of A-B ARF antagonism, leaving the relationship with the canonical pathway unclear. Mutants in tir1 afb2 ett were therefore generated in Arabidopsis and Capsella to assess the relationship between the two pathways, and their conservation in species with distinct fruit shapes. The data presented indicate conserved synergism between the two pathways in gynoecium development and suggest a role for ARF4 in the integration of these pathways in Brassicaceae with distinct fruit shapes.

Summary: An investigation of the relationship between ETT and ARF4, and canonical and ETT-mediated auxin signalling machineries in Arabidopsis and Capsella reveals conserved functions in Brassicaceae with distinct fruit shapes.