Phytochromes B, D, and E act redundantly to control multiple physiological responses in Arabidopsis.

Phytochrome-mediated perception of the ratio of red to far-red wavelengths in the ambient light environment is fundamental to plant growth and development. Such monitoring enables plants to detect neighboring vegetation and initiate avoidance responses, thus conferring considerable selective advantage. The shade avoidance syndrome in plants is characterized by elongation growth and early flowering, responses that are fully induced by end-of-day far-red light treatments. Elucidating the roles of individual phytochromes in mediating responses to red to far-red has however always been confounded by synergistic and mutually antagonistic coactions between family members. The creation of triple and quadruple mutants in Arabidopsis, deficient in multiple phytochromes, has revealed functional redundancy between phyB, D, and E in controlling flowering time, leaf development, and regulation of the homeobox gene, ATHB-2. In addition, mutant analysis suggests a possible novel role for phyC in suppressing ATHB-2 transcription in the light.