FASCICLIN-LIKE 18 Is a New Player Regulating Root Elongation in .

The plasticity of root development represents a key trait that enables plants to adapt to diverse environmental cues. The pattern of cell wall deposition, alongside other parameters, affects the extent, and direction of root growth. In this study, we report that FASCICLIN-LIKE ARABINOGALACTAN PROTEIN 18 (FLA18) plays a role during root elongation in . Using root-specific co-expression analysis, we identified to be co-expressed with a sub-set of genes required for root elongation. encodes for a putative extra-cellular arabinogalactan protein from the -gene family. Two independent T-DNA insertion lines, named and , display short and swollen lateral roots (LRs) when grown on sensitizing condition of high-sucrose containing medium. Unlike (), previously shown to display short and swollen primary root (PR) and LRs under these conditions, the PR of the mutants is slightly longer compared to the wild-type. Overexpression of the CDS complemented the root phenotype. Genetic interaction between either of the alleles and reveals a more severe perturbation of anisotropic growth in both PR and LRs, as compared to the single mutants and the wild-type under restrictive conditions of high sucrose or high-salt containing medium. Additionally, under salt-stress conditions, had a small, chlorotic shoot phenotype, that was not observed in any of the single mutants or the wild type. As previously shown for , the and root-elongation phenotype is suppressed by abscisic acid (ABA) and display hypersensitivity to the ABA synthesis inhibitor, Fluridon. Last, similar to other cell wall mutants, root elongation is hypersensitive to the cellulose synthase inhibitor, Isoxaben. Altogether, the presented data assign a new role for FLA18 in the regulation of root elongation. Future studies of the unique vs. redundant roles of FLA proteins during root elongation is anticipated to shed a new light on the regulation of root architecture during plant adaptation to different growth conditions.