Two chemically distinct root lignin barriers control solute and water balance

Abstract

Lignin is a complex polymer deposited in the cell wall of specialised plant cells, where it provides essential cellular functions. Plants coordinate timing, location, abundance and composition of lignin deposition in response to endogenous and exogenous cues. In roots, a fine band of lignin, the Casparian strip encircles endodermal cells. This forms an extracellular barrier to solutes and water and plays a critical role in maintaining nutrient homeostasis. A signalling pathway senses the integrity of this diffusion barrier and can induce over-lignification to compensate for barrier defects. Here, we report that activation of this endodermal sensing mechanism triggers a transcriptional reprogramming strongly inducing the phenylpropanoid pathway and immune signaling. This leads to deposition of compensatory lignin that is chemically distinct from Casparian strip lignin. We also report that a complete loss of endodermal lignification drastically impacts mineral nutrients homeostasis and plant growth.

Directed growth and fusion of membrane-wall microdomains requires CASP-mediated inhibition and displacement of secretory foci

“…In addition to the cell wall modification itself, the CS is characterized by the formation of a membrane domain, the CSD, that excludes most plasma membrane proteins and is tightly attached to the adjacent cell wall (Alassimone et al, 2010; Reyt et al, 2021; Roppolo et al, 2011). While CASP microdomain formation perfectly co-incides with the appearance of protein exclusion and membrane attachment, it could not be established whether CASPs are indeed required for these features.…”

Non-invasive hydrodynamic imaging in plant roots at cellular resolution

“…RMS imaging was used to investigate alterations of D 2 O dynamics and xylem water velocity in A. thaliana genotypes impaired in the integrity of their endodermal diffusion barriers. Measurements were performed on roots of wild-type plants (WT, Col-0); a WT line expressing the pCASP1::CDEF construct which degrades endodermal suberin (termed CDEF ) 15 ; and the sgn3-3 myb36-2 mutant, which displays no CS but normal suberization 16 . RMS imaging of “D 2 O wash-out” from individual protoxylem vessels revealed contrasting hydrodynamic behaviors.…”

“…This barrier is absent up to 3 mm from the protoxylem maturation point in the mutant esb1.1 (and by extension esb1.1 CDEF , whose hydraulic data is used to constrain the model parameters) before an ectopic CS is formed 19 . The CS is completely absent in sgn3-3 myb36-2 , even after the formation of the suberin lamellae, so that apoplastic flow in radial walls of endodermal cells may continue at all stages of maturation 16 . Second, the suberin lamellae, made of a waxy substance called suberin, is located between plasma membranes and primary walls on all sides of endodermal cells.…”

Cell-type specific transcriptomics reveals roles for root hairs and endodermal barriers in interaction with beneficial rhizobacterium

“…Col-0 seeds and mutants in Col-0 background: myb36-2/sgn3-3 (Reyt et al, 2021), cpc-1 and ttg1 (Wada et al, 1997; Walker et al, 1999) were surface sterilized and sown on agar-solidified Hoagland plates (as before). When 7-d-old, seedlings were transferred to agar-solidified Hoagland plates with 0% sucrose where WCS417 was mixed in the medium (as before).…”