Since the discovery in the 1990's of the first planet orbiting a distant star, the detection of hundreds of exo-planets have been confirmed. After these discoveries, the key issues are now to characterise these planetary systems and to understand how they forme and evolve. Another important issue is whether an "habitable'' zone for planets around stars exists or not. To answer these questions, it is mandatory to get a precise description of the main driver of the system: the star. The success of space missions based on stellar photometric observations, such as MOST, CoRoT and Kepler now makes possible the detailed study of the properties of stars. The presence of the PLATO and ECHO missions in the selection process for the ESA M3 mission will magnify the new possibilities opened by already launched missions. The first seismic analyses and interpretations performed in the past four years have demonstrated the potential of asteroseismology to investigate the physics of stars. In addition, the ultra-precise photometry provided by the aforementioned space experiments also allows new possibilities of investigation, for example in terms of magnetic activity through the study of the microvariability of the stars. The present proposal aims at precisely characterising the stars in order to determine their influence on their possible planetary system. As the determination of the size and mass of an exo-planet depends on that of the star, one of our goals is to obtain precise stellar mass and radius measurements. Physical conditions at the surface of a planet will depend on the radiative and magnetic interactions between the star and the planets: we therefore also aim at precise measurements of the star's luminosity and at a quantification of the star's magnetic activity and of their driving on the planetary system. Additional information such as the chemical characteristics of the star (helium and other element abundances), having a link with the process of planet formation, will be derived. The availability of space-borne observations providing photometric data of an unprecedented intrinsic quality (duration, precision, stability), coupled with the power of asteroseismic analysis now makes these objectives possible. Stellar modelling is the underlying tool for the interpretation of the results. The precision reached by observations calls for up-to-date stellar modelling that includes dynamical mechanisms such as transport of angular momentum by meridional circulation and internal gravity waves. As one of the main issues is the existence and extent of habitable zones around stars, our solar system will be used as a benchmark for the star-planet relation. More precisely, we will focus on the couple Sun-Mars, as this planet is thought to have lost its atmosphere because of the wind emitted by the young Sun. This will allow us to answer the question about the past of Mars and its possible habitability at the beginning of its history in the frame of the validation of our models in terms of magnetic activity. To sum up, we aim at providing the characteristics of the stellar radiative and magnetic driving on planets to experts in planetology. The underlying approach to our scientific program is the exploitation of stellar modelling tools combined with seismic observations of the best possible quality, in order to characterise the most precisely possible a star, and to be able to infer in a reliable manner the physical driving of the star in the star-planet relations.