Multiple photomorphogenic repressors work in concert to regulate Arabidopsis seedling development.

Light is both a source of energy and a critically important environmental signal for plant development. Through decades of research, 2 groups of photomorphogenic repressors have been identified. The first group is CONSTITUTIVE PHOTOMORPHOGENIC/DE-ETIOLATED/FUSCA (COP/DET/FUS), which were first identified by genetic screening and then by purification of protein complexes. Another group is the Phytochrome-Interacting Factors (PIFs), which were identified by yeast 2-hybrid screens using phyB as bait. How so many factors work together to repress photomorphogenesis has long been an interesting question. Previously, we demonstrated that CULLIN4 (CUL4) works as a core factor connecting the COP1-SPA complexes, the COP9 signalosome (CSN), and the COP10-DDB1-DET1 (CDD) complex. Recently, we showed that DET1 represses photomorphogenesis through positively regulating the abundance of PIF proteins in the dark. Dr. Huq and his colleagues reported that PIFs may enhance the function of COP1-SPA complexes to promote the degradation of HY5, and thus they synergistically repress photomorphogenesis in the dark. Though much work still needs to be done, these recent breakthroughs shed light on the regulatory relationships among these multiple photomorphogenic repressors.