Photoreceptors UVR8 and phytochrome B cooperate to optimize plant growth and defense in patchy canopies

Abstract

Light is a critical source of information for plants. Plants use the phytochromes (particularly phyB) to detect light signals associated with the proximity of competitors. A low ratio of red (R) to far-red (FR) radiation (R:FR) indicates increased competition intensity, and triggers morphological responses that allow the plant to escape shading from its neighbors (the shade avoidance syndrome, SAS). Recent evidence from studies on light regulation of plant immunity has suggested that plants may also use ultraviolet-B (UV-B, 290-315 nm) radiation as an indicator of competition intensity and light availability. In addition, recent studies have shown that UV-B radiation can strongly repress SAS responses triggered by low R:FR ratios. Ambient UV-B radiation causes damaging effects on plants, such as DNA damage, and also induces adaptive photomorphogenic responses acting through a specific UV-B photoreceptor (UVR8). Therefore, the possibility exists that plants integrate information perceived by phyB and UVR8 to make decisions about growth and defense when faced with a complex light environment, such as the one that characterizes vegetation canopies. In this Letter, we address this possibility and discuss how the interplay between UV-B and R:FR signaling fine tunes plant growth and defense to optimize resource utilization in patchy canopy environments.