The 14-3-3 isoforms chi and epsilon differentially bind client proteins from developing Arabidopsis seed.

The 14-3-3-protein family is prominently expressed during seed filling and modulates protein interactions and enzymatic activities, in a phosphorylation-dependent manner. To investigate the role(s) of 14-3-3 proteins in oilseed development, we have begun to characterize the Arabidopsis thaliana 14-3-3 "interactome" for two phylogenetically distinct isoforms. Proteins from developing Arabidopsis seed were incubated with a Sepharose affinity matrix containing covalently bound recombinant Arabidopsis 14-3-3 isoforms chi (χ) or epsilon (ε). Eluted proteins were quantitatively identified using GeLC-MS/MS coupled to spectral counting. Analysis of nine biological replicates revealed a total of 104 putative 14-3-3 binding proteins eluted from this affinity matrix compared to controls. Interestingly, these results imply that χ and ε could have distinct preferences for client proteins. Both isoforms interact with client proteins involved in various metabolic pathways, including glycolysis and de novo fatty acid synthesis. These results suggest 14-3-3 proteins interact with multiple biochemical processes of Arabidopsis seed development. Furthermore, these data suggest isoform specificity of client proteins and possibly even functional specialization between the 14-3-3 isoforms χ and ε in Arabidopsis seed development.