Disengagement of light responses in Arabidopsis by localized developmental factors.

Plant development and growth are profoundly influenced by environmental cues such as light intensity and composition. In particular, changes in red (600 nm to 700 nm) and far-red (700 nm to 750 nm) light inform about the threat of competing plants nearby, which deplete red light and generate an unfavorable shade environment enriched in far-red light (1). Plants detect red and far-red light using an evolutionarily conserved family of photoreceptors named phytochromes, which are activated by red light and inactivated by far-red light (2). Phytochromes play an important role in shaping plant architecture, in part, by restricting the rate of stem growth (3). When plants encounter a canopy of neighboring plants, the far-red light-enriched shade environment inactivates phytochromes to promote stem growth, thereby allowing the plants to escape shade via the so-called shade avoidance response (4, 5). In the plant model species Arabidopsis thaliana ( Arabidopsis ), phytochromes are ubiquitously expressed in all tissue/organ types throughout the life cycle (6). This expression pattern enables all tissues/organs to continuously monitor and respond to changes in the local light environment. However, intriguingly, shade does not elicit growth in all stem tissues: While the embryonic stem (hypocotyl) and the leaf petiole are exquisitely sensitive to shade, the internodes—which are located at the boundary region connecting the hypocotyl, the bases of the leaves, and the shoot apical meristem—are almost completely unresponsive (Fig. 1 A ) (7). The lack of … [↵][1]1Email: meng.chen{at}ucr.edu. [1]: #xref-corresp-1-1