Plants have evolved sophisticated photoreceptor systems to sense light conditions of the environment.Phytochromes are a major class of photoreceptors that are activated by red light to regulate physiological and photomorphogenic responses either directly or via gene regulation.Light perception by phytochromes depends on the association of tetrapyrrole chromophores.Ferredoxin-dependent bilin reductases (FDBRs) are required for synthesizing the chromophores.In plants,HY2 was known to be the only FDBR for producing the chromophore phytochromobilin.