Phytochrome E Plays a Role in the Suppression of Germination in Far-Red Light in Tomato.

As photoautotrophs, plants use light not only as a source of energy but also as cues for directing growth and development. Phytochromes comprise a small gene family of plant specific light receptors that absorb mostly in the red/far-red portion of the electromagnetic spectrum. These light receptors are well-studied in the model species Arabidopsis thaliana, yet much less is known about their functions in other species. We have generated CRISPR-induced mutations in SlPHYTOCHROME E (SlPHYE) and SlPHYF, produced higher order mutants, and characterized some of their physiological functions in tomato (Solanum lycopersicum). We report that SlphyE plays a major role in detecting far-red light, repressing germination when light conditions are unfavorable for establishing a new seedling. While SlphyE functions on its own, it also synergistically works with another phytochrome, SlphyB1, which by itself only plays a minor role in germination control. Aside from its role in far-red light detection, SlPhyE is also involved in perceiving red light, leading to the repression of hypocotyl elongation and the promotion of light avoidance growth in the roots. SlPhyF acts synergistically with phyB1 during photomorphogenesis but it is not involved in far-red light detection during germination.