Identification of New Components Involved in Cell Wall Deposition in Arabidopsis Lateral Root Elongation

The plasticity of root development represents a key trait enabling plants to adapt to every-changing abiotic stress conditions. Lateral roots are formed repetitively from the primary-embryonic root determining root system architecture. Both primary and lateral root growth extent and direction are largely determined by the pattern of plant cell wall deposition. Nonetheless, primary and lateral roots have been shown to display differential growth dynamics in responses to different environmental cues. We therefore hypothesized that specialized mechanisms are employed in the regulation of lateral vs. primary root elongation under abiotic stress conditions, partly through the regulation of cell wall deposition. Bioinformatics and next-generation genetic screen named PHANTOM were used in order to identify new components employed in this mechanism. Tissue-specific coexpression analysis led to the identification of a new role for the arabinogalactan extra-cellular protein FASCICLIN-LIKE 18 (FLA18) in the preferential regulation of lateral root elongation under stress conditions. Interestingly, double mutant with salt overly-sensitive 5/fla4 display an additive effect suggesting a role for FLA18 in both primary and lateral root elongation. As a complementary approach, we utilized the PHANTOM library, comprising artificial microRNAs (amiRNAs) designed to silence multiple family-members by single amiRNA construct, thereby eliminating functional redundancy between different family members. Preliminary results led to the identification of numerous lines with preferential-perturbation of lateral root elongation. In-depth study of FLA18 and the PHANTOM-lines identified is anticipated to shed new light on the mechanism involved in the regulation of primary vs. lateral root elongation determining root system architecture in changing environment.