Abstract The BTB/TAZ (BT) scaffold protein family has been recognized as a key regulator of nutrient signaling and developmental control in plants; however, its functions in woody species remain insufficiently understood. In this study, ten BT family members (PtoBTs) were identified in Populus tomentosa, and their roles in nitrate-regulated root development were investigated. High transcript abundance of PtoBT1 and PtoBT2 was detected in roots, and dynamic responses to nitrate availability were observed. Overexpression of PtoBT1B, PtoBT2A, or PtoBT2B was found to significantly inhibit root elongation and biomass accumulation, whereas RNA interference (RNAi)–mediated suppression of these genes was shown to promote root growth. Physiological and metabolomic analyses indicated that suppression of PtoBTs expression was associated with enhanced nitrate influx, upregulated activities of nitrogen-assimilation enzymes (GS and GOGAT), elevated free amino acid levels, and increased contents of indole-3-acetic acid (IAA), jasmonic acid (JA), and gibberellic acid (GA₃). By contrast, PtoBTs overexpression were associated with reduced activities of selected nitrate-assimilation–related enzymes and decreased levels of IAA, JA, and GA₃, whereas nitrate uptake was not significantly decreased. Collectively, these findings suggest that PtoBT1 and PtoBT2 act as negative regulators of root development and participate in integrating nitrate signaling with hormone homeostasis in a nitrate concentration–dependent manner. This study provides new insights into the molecular basis of root plasticity in trees and suggests potential genetic targets for improving nutrient-use efficiency in forest species.
Zi et al. (2026) studied this question.