Effects of cell wall synthesis on cell polarity in the red alga Porphyra yezoensis.

Polarity is a fundamental cell property essential for differentiation, proliferation and morphogenesis in unicellular and multicellular organisms. We have recently demonstrated that phosphatidylinositol 3-kinase (PI3K) activity is required for the establishment of anterior-posterior axis, leading to asymmetrical localization of F-actin in migrating monospores of the red alga Porphyra yezoensis. We also showed that the formation of the apical-basal axis via adhesion of monospores to the substratum after the cessation of migration requires newly synthesized proteins and does not depend on PI3K activity. However, little is known about the mechanism and regulation of axis conversion during development of monospores. In this addendum, we report our investigation as to the role of the cell wall in axis conversion. Our results indicate that inhibition of cell wall synthesis prevented the development of germlings. Also, defects in the cell wall disrupted the asymmetrical distribution of F-actin and inhibited the adhesion to the substratum that is required for establishment of apical-basal axis. Hence, we conclude that the cell wall is critical for the maintenance of cell polarity in migrating cells, which is indirectly involved in axis conversion via enabling monospores to adhere to the substratum.