The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) regulates various processes in plant growth and development independent of its conversion to ethylene, including cell wall expansion, stomatal guard mother cell division, pollen tube attraction etc. We are exploring the mechanism by which ACC acts to modulate plant development, focusing on the Arabidopsis root. In order to determine the kinetics of ethylene action in roots, we performed a time lapse study of root elongation in ein2,5 seedlings in response to exogenous ACC. We find that the inhibition of root elongation does not occur until after 30 hours of ACC treatment. Consistent with this, we see no changes in gene expression after 2 hours of ACC treatment. Transcriptome analysis of longer treatment (40 hours) revealed a set of ~200 differentially expressed genes. GO terms enriched among the up-regulated included hypoxia, abiotic stress, and ROS signaling while the down-regulated genes were enriched for genes involved in cell wall biogenesis. Among the down-regulated genes were a set of CLV3/ESR-RELATED (CLE) genes from the same clade. Previously, a multiple mutant line disrupted for the genes comprising this clade (cle1—cle7) were shown to promote lateral root growth in Arabidopsis (Nakagami et al., 2023). We confirmed that these cle1-7septuple mutant seedlings have more lateral roots and found that an acsoctuple mutant had fewer lateral roots compared to WT in presence of MCP. Further, treatment of wild-type seedlings with ACC promoted lateral root formation, and treatment of the acs octuple with exogenous ACC restores WT levels of lateral roots. These data suggest a model in which ACC transcriptionally down-regulates this clade of CLEs, which in turn increases lateral roots formation.