The OST subunit STT3A is required for root architecture and stress sensitivity by ensuring auxin transporter homeostasis

• STT3A loss-of-function disrupts root architecture and increases salt sensitivity. • N-glycosylation is required for the stability and membrane localization of ABCB transporters. • ABCB1, ABCB14, and ABCB19 are destabilized in stt3a-2 , impairing auxin transport. • PIN2 polarity is altered in stt3a-2 , likely reflecting secondary effects of disrupted transporter. • STT3A maintains auxin homeostasis to support root development and stress tolerance. N-glycosylation is an essential protein modification catalyzed by oligosaccharyltransferase (OST), with STT3A serving as its key catalytic subunit in Arabidopsis. While STT3A has been implicated in abiotic stress responses, its mechanistic role remains unclear. Here, we show that stt3a-2 mutant exhibits defective root development, including shortened lateral roots and root hairs, along with increased salt sensitivity. These phenotypes are linked to disrupted auxin distribution and are associated with impaired polar auxin transport. We demonstrate that STT3A-dependent N-glycosylation contributes to the stability and membrane localization of ABCB auxin transporters—ABCB1, ABCB14, and ABCB19—which are destabilized in stt3a-2 . Altered PIN2 localization is also observed, likely reflecting secondary effects of disrupted transporter homeostasis rather than direct N-glycosylation of PIN2 itself. Together, our findings support that STT3A-dependent N-glycosylation contributes to root development and influences salt stress sensitivity by ensuring proper auxin transporter function, thereby regulating auxin homeostasis and root architecture.