Updated project metadata. Lateral roots are essential components of the plant edaphic interface; contributing to water and nutrient uptake, biotic and abiotic interactions, stress survival, and plant anchorage. We have identified the TETRATRICOPEPTIDE-REPEAT THIOREDOXIN-LIKE 3 (TTL3) gene as being related to lateral root emergence and later development. Loss of function of TTL3 leads to a reduced number of emerged lateral roots due to delayed development of lateral root primordia. This trait is further enhanced in the triple mutant ttl1ttl3ttl4. TTL3 interacts with microtubules and endomembranes and is known to participate in the brassinosteroid signaling pathway. Both ttl3 and ttl1ttl3ttl4 mutants are less sensitive to brassinosteroid treatment in terms of lateral root formation and primary root growth. The ability of TTL3 to modulate biophysical properties of the cell wall was established under restrictive conditions of hyperosmotic stress and loss of root growth recovery, which was enhanced in ttl1ttl3ttl4. Timing and spatial distribution of TTL3 expression is consistent with its role in development of lateral root primordia before their emergence and subsequent growth of lateral roots. TTL3 emerged as a novel component of the root system morphogenesis regulatory network.