Abstract text: In plants, environmental exploration relies on the directional elongation of specialized organs, which emerges from directional cellular growth. This process is driven by cell wall loosening, which leads to irreversible yielding of the wall under turgor pressure. On the other hand, directionality of growth is primarily imposed by patterned deposition of stiff cellulose microfibrils which elastically constrain growth parallel to their net orientation of deposition.

However, it has been shown that plant cells can also grow directionally in the absence of cellulose anisotropy. For instance, in Arabidopsis thaliana lateral roots, a secretory trafficking pathway targeted to cell edges can control cell directional growth independently of cellulose patterning. While its cargo is still unknown, our data indicate that the wall at cell edges in lateral roots possesses specific biochemical and mechanical signatures, lost when the edge growth pathway is impaired. We hypothesize that these edge-based cell wall modifications allow polarized cell wall loosening, which constitutes an additional mode of directional growth control complementary to cellulose patterning. I will present the result of enzymatic wall modifications, micromechanical tests, and polysaccharide immunolocalization experiments, functionally testing this new hypothesis for plant directional growth control.