Local phytochrome signalling limits root growth in light by repressing auxin biosynthesis

• Published in: Journal of experimental botany Vol. 74; no. 15; pp. 4642 - 4653
• Main Authors: Spaninks, Kiki, Offringa, Remko
• Format: Journal Article
• Language: English
• Published: UK Oxford University Press 17.08.2023
• Subjects: Research Papers; phytochrome signalling; auxin biosynthesis; tomato; root growth; Arabidopsis
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/erad163

Abstract In nature, plant shoots are exposed to light whereas the roots grow in relative darkness. Surprisingly, many root studies rely on in vitro systems that leave the roots exposed to light whilst ignoring the possible effects of this light on root development. Here, we investigated how direct root illumination affects root growth and development in Arabidopsis and tomato. Our results show that in light-grown Arabidopsis roots, activation of local phytochrome A and B by far-red or red light inhibits respectively PHYTOCHROME INTERACTING FACTORS 1 or 4, resulting in decreased YUCCA4 and YUCCA6 expression. As a result, auxin levels in the root apex become suboptimal, ultimately resulting in reduced growth of light-grown roots. These findings highlight once more the importance of using in vitro systems where roots are grown in darkness for studies that focus on root system architecture. Moreover, we show that the response and components of this mechanism are conserved in tomato roots, thus indicating its importance for horticulture as well. Our findings open up new research possibilities to investigate the importance of light-induced root growth inhibition for plant development, possibly by exploring putative correlations with responses to other abiotic signals, such as temperature, gravity, touch, or salt stress. In widely used in vitroplant growth systems, illumination of roots leads to suboptimal auxin levels in root apical meristem, limiting root growth in response to red and far-red light.