Reduced RG-II pectin dimerization disrupts differential growth by attenuating hormonal regulation.

Abstract

Defects in cell wall integrity (CWI) profoundly affect plant growth, although, underlying mechanisms are not well understood. We show that in <i>Arabidopsis mur1</i> mutant, CWI defects from compromising dimerization of RG-II pectin, a key component of cell wall, attenuate the expression of auxin response factors <i>ARF7-ARF19</i>. As a result, polar auxin transport components are misexpressed, disrupting auxin response asymmetry, leading to defective apical hook development. Accordingly, <i>mur1</i> hook defects are suppressed by enhancing <i>ARF7</i> expression. In addition, expression of brassinosteroid biosynthesis genes is down-regulated in <i>mur1</i> mutant, and supplementing brassinosteroid or enhancing brassinosteroid signaling suppresses <i>mur1</i> hook defects. Intriguingly, brassinosteroid enhances RG-II dimerization, showing hormonal feedback to the cell wall. Our results thus reveal a previously unrecognized link between cell wall defects from reduced RG-II dimerization and growth regulation mediated via modulation of auxin-brassinosteroid pathways in early seedling development.