Functional characterization of AoPLL16 in salt tolerance regulated by AobHLH31 in Aquilegia oxysepala

Salt stress severely restricts plant growth and impairs ornamental quality. The plant cell wall acts as the primary physical barrier to salt stress, and its structural integrity is critical for plant salt‑tolerance capacity. As key regulators of cell wall dynamics, pectate lyase‑like (PLL) proteins mediate cell wall remodeling via homogalacturonan depolymerization. Nevertheless, their specific functions and underlying regulatory mechanisms in salt‑stress adaptation of ornamental plants remain largely uncharacterized. In this study, we used Aquilegia oxysepala-a characteristic perennial ornamental herb native to Northeast China-to characterize the salt‑tolerance function and molecular regulatory mechanism of the salt‑inducible gene AoPLL16. AoPLL16 overexpression aggravated tobacco salt sensitivity, as evidenced by declined photosynthetic efficiency, inhibited antioxidant enzyme activities, attenuated cell wall thickness, and decreased pectin accumulation. Further functional validation verified that the upstream bHLH transcription factor AobHLH31 mediates tobacco salt tolerance by directly binding to the AoPLL16 promoter to repress its transcription. This study preliminarily identifies an AobHLH31‑AoPLL16 regulatory cascade: upon salt stress, AobHLH31 represses AoPLL16 transcription to remodel cell wall composition and structure, conferring salt tolerance to A. oxysepala.