Analysis of protein binding characteristics among Arabidopsis BBX protein family

Plants have evolved various mechanisms of adjusting their diurnal and seasonal growth and development in response to variations in day length and light quality. This plasticity is facilitated by intricate regulatory networks that comprise transcription factors, whose expression is modulated by the activity of photoreceptors. In Arabidopsis , B-box (BBX) transcription factors, which contain one or two Zn-ligating B-box motifs in their N-termini, serve as key mediators of light signaling for photomorphogenesis, shade avoidance, and photoperiodic flowering. While multiple BBX proteins may function as a single regulatory unit, the binding networks that form among members of the BBX family have not been extensively investigated. Here, we have demonstrated that the homodimerization of two B-box motifs containing CONSTANS protein (BBX1), which regulates light signaling and is the most extensively characterized among all BBX proteins, requires at least three B-box motifs. Therefore, the number of B-box motifs may significantly influence heterodimerization among BBX family members. An interactome analysis of all 32 known B-box family members revealed that the binding affinity between group III and V proteins with only one B-box motif is relatively weaker than that observed among other group members. In fact, the group V proteins BBX26 and BBX27 rarely interact with other BBX members. Taken together, the results of this study emphasize the importance of the B-box motif in network formation among BBX proteins and provide insights into investigating the various signaling pathways mediated by these networks.