Functional distinction of hyphal compartments

Hyphae grow of higher fungi grow at their apex and are compartmentalized by septa that have a central pore enabling cytoplasmic streaming. Peroxisome-derived Woronin bodies however can plug these pores. Incidence of plugging increases in time switching the unicellular organization of young hyphal compartments into a multicellular one in older compartments. It was assessed whether the multicellular organization contributes to apical growth of hyphae and how growth is affected when Woronin bodies are absent. Hyphae of the wildtype strain and a ΔhexA strain that lacks Woronin bodies had a similar morphology and growth rate. A total of 58% and 17% of the hyphae continued growing, respectively, after dissecting the 2^nd compartment. Growth rate of these hyphae was not affected, even when the carbon or nitrogen source was limiting. Dissection at a fixed position of 400 µm from the apex revealed that all wild-type and ΔhexA hyphae stopped growing when the first septum was positioned > 400 µm from the apex, while 81 % and 57% of the hyphae, respectively, continued growing when the first septum located < 400 µm from the tip. When apical compartments were dissected, normal growth from subapical compartments was recovered in wild type hyphae but not in ΔhexA hyphae. Together, we showed for the first time that apical compartments are self-sustaining in growth