Regulation of lateral root development via the HY5 Transcription Factor

Plant Cell. Plants sense competitors through phytochromes. Phytochromes detect the reflection of far-red light from nearby plants, resulting in a reduced red:far-red (R:FR) ratio. The reduced ratio causes shade avoidance responses which modify shoot and root system architecture. This paper by van Gelderen and colleagues identifies a regulatory mechanism of root system architecture induced by light detection in the shoot using Arabidopsis thaliana. This novel mechanism is identified through microscopy, gene expression and mutant studies. Low R:FR is found to decrease lateral root density, which is regulated by the phytochrome-dependent accumulation of the HY5 (ELONGATED HYPOCOTYL 5) transcription factor. HY5 decreases the abundance of PIN3 (PIN-FORMED 3) and LAX3 (LIKE-AUX1 3) auxin transporters at the plasma membrane. This causes a reduction of the auxin signal to cortex cells, reducing the growth of lateral roots. This mechanism connects the sensing of light at the shoot to root structure and coordinates resource portioning. (Summary by Julia Miller) Plant Cell.  10.1105/tpc.17.00771