At dawn of a scorching summer day, land plants must anticipate upcoming extreme midday temperatures by timely establishing molecular defenses that can maintain heat-labile membranes and proteins in a functional state. A gradual morning pre-exposure to increasing sub-damaging temperatures induces the accumulation of heat-shock proteins (HSPs) that are central to the onset of plant acquired thermotolerance (AT). In an attempt to gain knowledge on the mechanisms of AT in the model land plant Physcomitrium patens, we used label-free LC-MS/MS proteomics to quantify the accumulated and depleted proteins before and following a mild heat-priming treatment.