Casparian strip diffusion barrier in Arabidopsis is made of a lignin polymer without suberin

Abstract

Casparian strips are ring-like cell-wall modifications in the root endodermis of vascular plants. Their presence generates a paracellular barrier, analogous to animal tight junctions, that is thought to be crucial for selective nutrient uptake, exclusion of pathogens, and many other processes. Despite their importance, the chemical nature of Casparian strips has remained a matter of debate, confounding further molecular analysis. Suberin, lignin, lignin-like polymers, or both, have been claimed to make up Casparian strips. Here we show that, in Arabidopsis, suberin is produced much too late to take part in Casparian strip formation. In addition, we have generated plants devoid of any detectable suberin, which still establish functional Casparian strips. In contrast, manipulating lignin biosynthesis abrogates Casparian strip formation. Finally, monolignol feeding and lignin-specific chemical analysis indicates the presence of archetypal lignin in Casparian strips. Our findings establish the chemical nature of the primary root-diffusion barrier in Arabidopsis and enable a mechanistic dissection of the formation of Casparian strips, which are an independent way of generating tight junctions in eukaryotes.root development | plant nutrition | polarized epithelium

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

“…S2A and S3A). Propidium iodide (PI) is a fluorescent dye used as an apoplastic tracer whose movement into the inner cell layer of the stele is blocked by Casparian strips (2). Staining with PI revealed that esb1-1 shows delayed barrier development ( absence of ESB1, it is possible that polymerization of monolignols, usually directed by localized NADPH oxidases and peroxidases (6), does not proceed normally, as indicated by the islands of lignin observed in esb1-1.…”

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

“…The endodermis protects the root vasculature from the entry of harmful toxins and pathogens by means of a cell-wall modification called the Casparian strip (1). This lignin-composed extracellular barrier prevents the passive flow of water and solutes into and out of the vasculature (2). To enter the vasculature, ions must pass through the endodermis, which selectively filters nutrients.…”

PDH45overexpressing transgenic tobacco and rice plants provide salinity stress tolerance via less sodium accumulation

“…18,19 Although exposing the rice under salinity stress leads to the deposition of suberin that further provides strength to the apoplastic barriers and such barriers block Na C transport to shoots. 16 The salinity tolerant variety (Pokkali) revealed more extensive hydrophobic barriers in its roots as compared to the salinity susceptible variety (IR20). 17,20 The PDH45 overexpression enhances salinity tolerance without compromising yield as compared to WT (IR64).…”

“…16 Further, bypass flow closely paralleled the extent of suberin deposition over the course of exposure to salinity stress and is negatively correlated with suberin deposits. 17 CoroNa Green AM binds with sodium (Na C ) and is specific Na C indicator that shows increase in fluorescence intensity indicates increasing Na C accumulation.…”