Distinct phytochrome-specific regulation of tomato sugar metabolism and plant architecture by far-red light

Phytochromes are a family of plant photoreceptors specialized in detecting red and far-red light (FR). Increased FR levels can trigger the shade avoidance syndrome, typically leading to morphological adjustments enhancing light perception. FR can also increase plant sugar levels by an unknown mechanism, and the roles of individual phytochromes in these responses remain largely unclear. Here, we used reverse genetics and FR trials in tomato (Solanum lycopersicum cv. Moneymaker) to assess the involvement of five phytochromes on different architectural, physiological, and sugar metabolism-related changes. Although FR had no direct positive effect on leaf photosynthesis, overall plant photosynthetic capacity increased, likely due to FR-induced architectural changes improving light capture. We found that phyB2 was involved in regulating this whole-plant photosynthesis response to FR. Our results using phy mutants indicated that FR can also directly affect tomato sugar metabolism independently of architectural and physiological changes. We found a critical role for phyE in regulating carbohydrate levels. We also found that phyB1 and phyB2 regulate source-sink dynamics under FR, and that phyA is potentially a negative regulator of sink strength under FR. Collectively, our work revealed distinct roles for individual phytochromes in coordinating FR-specific architectural and sugar metabolism responses in tomato.