Arabidopsis 14-3-3 proteins: fascinating and less fascinating aspects

Abstract

14-3-3 Dimers are well known to interact with diverse target proteins throughout eukaryotes. Most notably, association of 14-3-3s commonly requires phosphorylation of a serine or threonine residue within a specific sequence motif of the client protein. Studies with a focus on individual target proteins have unequivocally demonstrated 14-3-3s to be the crucial factors modifying the client's activity state upon phosphorylation and, thus, finishing the job initiated by a kinase. In this respect, a recent in-depth analysis of the rice transcription factor FLOWERING LOCUS D1 (OsFD1) revealed 14-3-3s to be essential players in floral induction. Such fascinating discoveries, however, can often be ascribed to the random identification of 14-3-3 as an interaction partner of the favorite protein. In contrast, our understanding of 14-3-3 function in higher organisms is frustratingly limited, mainly due to an overwhelming spectrum of putative targets in combination with the existence of a multigene 14-3-3 family. In this review we will discuss our current understanding of the function of plant 14-3-3 proteins, taking into account recent surveys of the Arabidopsis 14-3-3 interactome.

Keywords: 14-3-3; interactome.

Figure 1

Ribbon plot of a 14-3-3 dimer (gray) in complex with two phosphopeptides derived from the transcription factor OsFD1 (orange, the phosphorylated residue is indicated by an arrow, respectively) and two Hd3a proteins [color coded from the N-terminus (blue) to the C-terminus (red)] (Taoka et al., 2011). While binding of the OsFD1 phosphopeptides occurs in an extended conformation within the amphipathic groove of each 14-3-3 monomer, the “florigen” Hd3a attaches to the “outside” of the groove, respectively.