Protein-Protein Interaction and Intercellular Movement of AT-HOOK MOTIF NUCLEAR LOCALIZED PROTEIN3 (AHL3) / AHL4 Transcriptional Factors

Abstract

Interaction and movement of various proteins are critical steps for deciding a cell fate. Recently, two novel factors, AT-HOOK MOTIF NUCLEAR LOCALIZED PROTEIN 3 (AHL3) and AHL4 were reported to define xylem boundary in the Arabidopsis root. These two factors interact with each other and move into neighbor cells. However, which domain of these proteins are participating in the process of interaction and movement is not clear. AHL gene family member contains two conserved domains: AT-hook motif and plant and prokaryote conserved (PPC) domain. We found that PPC domain of AHL4 protein is involved in interaction with other AHL proteins including AHL3 protein. To understand the importance of amino-acid sequence of PPC domain in the interaction, we mutated some amino-acids in PPC domain of AHL4 protein that are predicted to affect protein-protein interaction based on 3-D structure. Yeast two hybrid assay indicated that mutated AHL4 and AHL3 no longer interact each other. Furthermore, AHL3 and AHL4 interact with not only each other but also other AHLs. These protein interaction data suggest the possibility that certain amino acids of PPC domain are important for forming protein complex between AHL proteins. Moreover, swapping PPC domain between two different AHL proteins induces the change of AHL movement. Therefore, the possibility suggests that PPC domain which is related to the interaction between AHL proteins is also participated in the movement of AHL protein.