Root cell walls constrain the development of lateral root primordia into lateral roots

Plants adapt to their unique soil environments by altering the number of lateral roots postembryonically. Arabidopsis seedlings grown on media respond to changes in osmotic potential and sucrose availability by simultaneously altering lateral root formation and shoot size. However, lateral root formation is repressed independently of shoot size with increased environmental nitrate concentration. Novel mutants have previously been identified that exhibit increased lateral root formation on screening conditions containing high amounts of nitrate salts. Eight mutants have been characterized in detail and were found to have increased lateral root formation due to at least three distinct mechanisms. The causal mutation in one of these mutants was found to alter a gene recently characterized to be involved in cell-wall biosynthesis. Mutations in this gene result in a reduction in the frequency in which lateral root primordia emerge to form lateral roots. However, the number of initiated primordia in this mutant is unaltered. Screening of other previously characterized cell wall mutants revealed that many also exhibit altered lateral root formation. This work suggests that proper cell wall biosynthesis is required for the normal process of lateral root emergence in Arabidopsis grown on media.