Universal modules for decoding amplitude and frequency of Ca2+ signals in plants

O_LICalcium signals are fundamental for plants and play a crucial role in long-term processes such as growth and development, as well as in rapid responses to environmental stimuli and stress factors. Nevertheless, the mechanisms involved in decoding calcium signal in plants are still largely unclear. C_LIO_LIHere, we have addressed the question of calcium signal decoding in a bottom-up modelling approach. We started with the thermodynamics of Ca2+ binding to a Ca2+ binding protein (CBP), e.g. via EF hands. Remarkably, Ca2+ binding properties of the EF hands do not coincide with the Ca2+ sensitivity of the protein containing these EF hands. C_LIO_LIIn analysing the next levels of complexity, we identified six universal fundamental Ca2+-decoding modules, in which Ca2+ either interacts directly with a target protein (TP) or modulates its activity via a CBP. These modules are the basic units that enable the amplitude and frequency of Ca2+ signals to be decoded. Representatives of these modules are omnipresent in plant cells. They straightforwardly explain the puzzling finding that Ca2+-dependent kinases exhibit different Ca2+-sensitivities when tested with different substrates. C_LIO_LIIn-depth analysis of the properties of the modules provides a fundamental theoretical basis for understanding Ca2+ signal decoding and may contribute to finding the "Rosetta Stone" for Ca2+ signals in plants. C_LI