A developmental framework for endodermal differentiation and polarity

Abstract

The endodermis is a root cell layer common to higher plants and of fundamental importance for root function and nutrient uptake. The endodermis separates outer (peripheral) from inner (central) cell layers by virtue of its Casparian strips, precisely aligned bands of specialized wall material. Here we reveal that the membrane at the Casparian strip is a diffusional barrier between the central and peripheral regions of the plasma membrane and that it mediates attachment to the extracellular matrix. This membrane region thus functions like a tight junction in animal epithelia, although plants lack the molecular modules that establish tight junction in animals. We have also identified a pair of influx and efflux transporters that mark both central and peripheral domains of the plasma membrane. These transporters show opposite polar distributions already in meristems, but their localization becomes refined and restricted upon differentiation. This "central-peripheral" polarity coexists with the apical-basal polarity defined by PIN proteins within the same cells, but utilizes different polarity determinants. Central-peripheral polarity can be already observed in early embryogenesis, where it reveals a cellular polarity within the quiescent center precursor cell. A strict diffusion block between polar domains is common in animals, but had never been described in plants. Yet, its relevance to endodermal function is evident, as central and peripheral membranes of the endodermis face fundamentally different root compartments. Further analysis of endodermal transporter polarity and manipulation of its barrier function will greatly promote our understanding of plant nutrition and stress tolerance in roots.Casparian strips | cell polarity | root development | endodermis | Arabidopsis

Dirigent domain-containing protein is part of the machinery required for formation of the lignin-based Casparian strip in the root

“…Fluorol yellow staining was performed as described (28). For assay of the apoplastic barrier, seedlings were incubated in the dark for 10 min in a fresh solution of 15 μM (10 μg/mL) PI and rinsed twice in water (29). For quantification, "onset of elongation" was defined as the point where an endodermal cell in a median optical section was more than twice its width.…”

Polarization of IRON-REGULATED TRANSPORTER 1 (IRT1) to the plant-soil interface plays crucial role in metal homeostasis

“…Lateral polarity in plant roots was described first in rice for the As/Si transporters Lsi1, Lsi2 (22), and in Arabidopsis for the boron transporter BOR4 (23). Then an increasing number of transporters were demonstrated to be laterally polarized in Arabidopsis roots such PDR8/PEN3, BOR1, NIP5;1, PIS1/PDR9/ABCG37, and NRT2.4 (24)(25)(26)(27)(28). However, the molecular mechanisms controlling lateral polarity are still unclear.…”

MYB36 regulates the transition from proliferation to differentiation in the Arabidopsis root

“…Barrier assays assessing Casparian strip function were performed as previously described (14). Briefly, seedlings were incubated in the dark for 10 min in fresh 10 μg/mL propidium iodide (Invitrogen) and rinsed two times in water.…”