Summary of the interactions between symbionts in lichen Endocarpon pusillum . The lectins lacking signal peptides, which are shown as ellipse marked with L, act as recognition factors in the direct contact between E. pusillum and D. chodatii. After it is captured by the compatible fungal partner, the photosynthetic products sorbitol (S), glucose (G) and sucrose (G-F) are released from the phycobiont D. chodatii. These sugars are then absorbed through sugar transporters of E. pusillum and converted into glucose or fructose to support fungal metabolism. In addition, there are a small amount of other uncertainty carbon sources (X) released by the phycobiont, and the mycobiont can also utilize mannitol (M) from environment. At the same time, organic and inorganic nitrogen, together with various ions in the environment, are transferred into E. pusillum. In fungal cells, these substances may be converted into the forms preferred by the phycobiont and are then delivered to D. chodatii.