Abstract: ETTIN is an atypical member of the AUXIN RESPONSE FACTOR family of transcription factors, which plays a crucial role in tissue patterning in the Arabidopsis thaliana gynoecium.

Though recent insights have provided valuable information on ETT's interactions with other components of auxin signaling, the biophysical mechanisms linking ETT to its ultimate effects on gynoecium morphology were until now unknown.

Here, using techniques to assess cell-wall dynamics during gynoecium growth and development, we provide a coherent body of evidence to support a model in which ETT controls the elongation of the valves tissues of the gynoecium through the positive regulation of pectin methylesterase (PME) activity in the cell wall.

This increase in PME activity results in an increase in the level of demethylesterified pectins and a consequent reduction in cell wall stiffness, leading to elongation of the valves.

Though similar biophysical mechanisms have been shown to act in the stem apical meristem, leading to the expansion of organ primordia, our findings represent a new case in which the regulation of cell-wall stiffness through the covalent modification of pectin has been shown to contribute to tissue patterning within a developing plant organ.

ETTIN is an atypical member of the AUXIN RESPONSE FACTOR family of transcription factors, which plays a crucial role in tissue patterning in the Arabidopsis thaliana gynoecium. Though recent insights have provided valuable information on ETT's interactions with other components of auxin signaling, the biophysical mechanisms linking ETT to its ultimate effects on gynoecium morphology were until now unknown. Here, using techniques to assess cell-wall dynamics during gynoecium growth and development, we provide a coherent body of evidence to support a model in which ETT controls the elongation of the valves tissues of the gynoecium through the positive regulation of pectin methylesterase (PME) activity in the cell wall. This increase in PME activity results in an increase in the level of demethylesterified pectins and a consequent reduction in cell wall stiffness, leading to elongation of the valves. Though similar biophysical mechanisms have been shown to act in the stem apical meristem, leading to the expansion of organ primordia, our findings represent a new case in which the regulation of cell-wall stiffness through the covalent modification of pectin has been shown to contribute to tissue patterning within a developing plant organ.

Source: Evidence for the control of Arabidopsis gynoecium morphogenesis by ETTIN via cell wall dynamics. Amélie Andres-Robin, Mathieu Reymond, Antoine Dupire, Virginie Battu, Nelly Dubrulle, Grégory Mouille, Valérie Lefebvre, Jerome Pelloux, Arezki Boudaoud, Jan Traas, Charles Patrick Scutt, Françoise Monéger. ASPB, September 2018.