Abstract
Production of reactive oxygen species (ROS) by NADPH oxidases (NOXs) impacts many processes in animals and plants, and many plant receptor pathways involve rapid, NOX‐dependent increases of ROS. Yet, their general reactivity has made it challenging to pinpoint the precise role and immediate molecular action of ROS. A well‐understood ROS action in plants is to provide the co‐substrate for lignin peroxidases in the cell wall. Lignin can be deposited with exquisite spatial control, but the underlying mechanisms have remained elusive. Here, we establish a kinase signaling relay that exerts direct, spatial control over ROS production and lignification within the cell wall. We show that polar localization of a single kinase component is crucial for pathway function. Our data indicate that an intersection of more broadly localized components allows for micrometer‐scale precision of lignification and that this system is triggered through initiation of ROS production as a critical peroxidase co‐substrate.
Highlights
Present address: Umeå Plant Science Centre (UPSC), Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences (SLU), 90183, Umeå, Sweden
This myrpalm SGN1-mCitrinerine (Citrine) variant was expressed under the control of the endodermis-specific CASP1 promoter, which is strongly active during Casparian strip formation and complemented the sgn1 barrier phenotype (Fig. EV 1A)
Both variants were excluded from the central position where the Casparian strip domain is formed (Fig. EV 1B) and the localization patterns of the two variants did not change when introgressed into sgn1, sgn3 or cif1 cif2 mutants (Fig. 1C, 1D)
Summary
Named Casparian strips (CS), these ring-like lignin structures fuse into a supracellular network, establishing a tissue-wide, extracellular diffusion barrier (Fig. 1A), analogous to epithelial tight junctions in animals (Geldner, 2013; Barberon & Geldner, 2014). Functionality of this barrier can be visualized by a block of penetration of a fluorescent cell wall dye, propidium iodide, into the vasculature (Alassimone et al, 2010; Naseer et al, 2012). CIF1 and 2 peptides do not express in the endodermis, where the CS is formed, but in the stele Both SGN1 and SGN3 present specific localization on the endodermal plasma membrane; SGN3 receptor-like kinase resides along both sides of the CS, while palmitoylated SGN1 polarly localizes on cortex facing (outer) plasma membranes (Doblas et al, 2017)
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