Lipocalins regulate development and various stress responses in Physcomitrium patens

Major physiological and developmental innovations are key to land-plant adaptation and evolution, but their genetic basis remains to be fully understood. Here, we show that lipocalins in the moss Physcomitrium patens regulate various physiological and developmental processes. Phylogenetics analyses reveal three major groups of plant lipocalins, including a newly identified group that is restricted to seedless plants. We demonstrate that the temperature-induced lipocalin gene in P. patens (PpTIL) is functionally conserved with flowering plant homologs in response to abiotic stresses. PpTIL not only regulates protonemal development and the transition from two-dimensional to three-dimensional growth but also affects many other processes, such as lipid transport and metabolism, auxin biosynthesis and transport, and chlorophyll catabolism. Further, PpTIL also operates antagonistically with SAFEGUARD1 in protecting chloroplast grana and envelopes from singlet oxygen stress. These findings provide major insights into the role of lipocalins in land-plant evolution.