Electron transfer between the major complexes of the photosynthetic apparatus is mediated by small electron transfer proteins. In order to fulfill their role, these proteins have to form interactions which are on one hand very specific, but simultaneously match multiple target complexes. This trait triggered a synergized evolutionary path, in which a change in one complex initiated adequate adaptations in matching residues of other complexes. In this study, we examined plastocyanin (PC) binding and electron transfer with both photosystem I (PSI) and cytochrome b6f (cyt b6f), and show the synergetic adaptations between these three enzymes. Furthermore, we explored the effects of PC phosphorylation on these interactions. To do so, we generated several recombinant variants of PC, in which we genetically engineered two of the phosphorylated residues (S10 & S49). We studied the kinetics of both Cytf oxidation and P700 re-reduction by measuring fast optical spectroscopy. We also conducted chemical protein crosslinking and structural proteomics to gain further insights on the interaction between PC and cyt b6f. Our results show that the phosphorylation mode of PC alters the conformation in which they establish binding and electron transfer, and generated new models which elaborate the mechanism of this adaptation. To further address electron transfer into cyt b6f via PSI reduced ferredoxin, we generated site-directed mutants in the N-terminal domain of cyt b6f subunit IV by chloroplast transformation. These mutations impact state transitions, electron transfer within and into cyt b6f as revealed by proteomics, fluorescence and fast optical spectroscopy.