Oeiras, 02.10.2015

Plant roots are able to sense mechanical stimuli, such as touch or gravity, and respond by altering growth direction. But how sensing the world connects to this ability to respond is not really known. Now a group of plant researchers from the GPlantS Lab shows that specific protein degradation is required for mechanical sensing in rice roots. The work is published in Plant Physiology.

Unlike animals, plants cannot escape from environmental annoyances. So plants have developed intricate mechanisms to sense and cope with different stimuli. For example, when exploring the soil, roots must know up from down and go around the obstacles they encounter. The perception of an obstacle and signaling mechanisms must have a coordinated response to modulate growth accordingly. Many studies have tried to address how this occurs. In this study, researchers focused on root growth in rice plants.

In response to touch, roots wave, skew and curl, a set of behaviors thought to facilitate root penetration in the soil, promote interaction with microorganisms, and increase the plant’s structural support. Previously, rice root curling was shown to be dependent on a particular gene (OsRMC). However, not much was known on why and how these root curls occurred. In this study, ITQB researchers (in collaboration with reserchers in the University of Wisconsin, USA) showed that rice root curling is dependent on a mechanical stimulus. Furthermore, they showed that silencing another gene (OsHOS1-  identified previously by this lab), rendered roots unable to curl when encountering a mechanical barrier. The absence of this mechanical “feeling” was correlated with the up-regulation of OsRMC and could be reverted by the addition of jasmonic acid, a plant hormone known to be involved in the modulation of mechanical responses (e.g., tendrils) but never identified in root mechanical responses.

The protein OsHOS1 is known to mediate protein degradation through the proteasome, a complex of proteins that degrade unneeded or damaged proteins. So researchers further investigated what were the targets of OsHOS1 and identified two transcription factors, which in turn control the expression of the OsRMC gene involved in root curling.

Researchers speculate that root curling upon encountering a physical barrier may be advantageous for rice plants, by creating a sort of anchor that fixes the growing seedling to the upper layers of soil.

Original Article

Plant Physiology (2015) doi: http:/​/​dx.​doi.​org/​10.​1104/​pp.​15.​01131

The rice E3 ubiquitin ligase OsHOS1 modulates the expression of OsRMC, a gene involved in root mechano-sensing, through the interaction with two ERF transcription factors

Tiago Filipe Lourenço, Tânia Sofia Serra, André Miguel Cordeiro, Sarah J. Swanson, Simon Gilroy, Nelson Jose Madeira Saibo and M. Margarida Oliveira