Seminars

Plant growth ultimately depends on fixed carbon, thus the available light for photosynthesis. Due to canopy light absorption properties, vegetative shade combines low blue (LB) light and a low red to far-red ratio (LRFR). In shade-avoiding plants, these two conditions independently trigger growth adaptations to enhance light access. However, how these conditions, differing in light quality and quantity, similarly promote hypocotyl growth remains unknown. Using RNA sequencing we show that these two features of shade trigger different transcriptional reprogramming. LB induces starvation responses, suggesting a switch to a catabolic state. Accordingly, LB promotes autophagy (Ince et al., 2022). In contrast, LRFR promotes anabolism by enhancing allocation of newly fixed carbon to the hypocotyl to for example promote biosynthesis of lipids required for cell growth in the hypocotyl (De Wit et al., 2018; Ince et al., 2022). We propose that vegetative shade enhances hypocotyl growth by combining autophagy-mediated recycling and promotion of specific lipid biosynthetic processes. I will discuss mechanisms underlying LRFR-induced resource allocation and how shade cues promote autophagy.