Few atypical aspartic proteases (APs) present in plants have been functionally studied to date despite having been implicated in developmental processes and stress responses， and diverse biochemical properties were reported for these enzymes. Here we characterize a novel atypical AP that we name ATYPICAL ASPARTIC PROTEASE IN ROOTS 1 (ASPR1)， denoting its expression in Arabidopsis roots. Recombinant ASPR1 produced by transient expression in N. benthamiana was active and displayed atypical properties， combining optimum acidic pH， partial sensitivity to pepstatin and pronounced sensitivity to redox agents， and unique specificity preferences resembling those of fungal APs. ASPR1 overexpression suppressed primary root growth and lateral root development， implicating a previously unknown biological role for an AP. Quantitative comparison of WT and aspr1 root proteomes revealed deregulation of proteins associated with both ROS and auxin homeostasis in the mutant. Together， our findings on ASPR1 reinforce the varied pattern of enzymatic properties and biological roles of atypical APs and raise exciting questions on how these distinctive features impact functional specialization among these proteases.