Polaritome: comprehensive identification of polarly-localized proteins in Arabidopsis thaliana

The establishment of cell polarity is a critical biological process essential for
cellular function and the morphogenesis of multicellular organisms. In plants, various
membrane proteins, including transporters, channels, and receptors, are localized to
specific domains of the plasma membrane (PM) in alignment with the cell polarity axes.
In roots, lateral cell polarity, aligned along the radial axis, is crucial for the directional
movement of inorganic nutrients from the soil to the vasculature and for the efflux of toxic
solutes, such as heavy metals and excessive boric acid, back into the soil. But how is
lateral cell polarity established in plants? While in animals, polarity axis-defining proteins
(polarity landmarks) have been identified through genetic approaches, such proteins are
not conserved in plants. Genetic analyses in plants are likely impeded by gene duplication
or embryonic lethality, which may explain why few genes involved in the regulation of cell
polarity have been identified in plants. Recently, we identified an uncharacterized
receptor-like kinase, DUAL-POLAR KINASE (DPK), which localizes to the inner PM
domain in the endodermis and the outer PM domain in the epidermis and cortex. In this
study, we conducted spatially-resolved proteomics using TurboID, a proximity-labeling
enzyme fused with polarly localized proteins including DPK. Through this method, we
identified several uncharacterized protein families localized to the PM in polar manners,
collectively termed the Polaritome. In this symposium, we will discuss the roles of these
proteins in the plant cell polarization machinery.