Overexpression of PtrPIP2:4 Accelerates Adventitious Root Emergence, Promotes Adventitious Root Elongation, and...

Plasma membrane intrinsic proteins (PIPs), a subfamily of aquaporins (AQPs), play critical roles in various physiological processes in plants, including the transport of water and CO₂, regulation of stomatal movement, absorption of neutral molecules and nutrients, and H₂O₂ signaling. Nevertheless, the functions of PIP aquaporins in adventitious root formation in trees are still poorly understood. PtrPIP2:4 is specifically expressed in roots, and PtrPIP2:4 fused with GFP localizes to the plasma membrane. Overexpression of PtrPIP2:4 significantly accelerated adventitious root induction in poplar. Stem cuttings from overexpression lines exhibited more rapid rooting compared to wild-type (WT) plants, although the total number of adventitious roots did not differ significantly. Additionally, the number of lateral roots was markedly increased in PtrPIP2:4 overexpression lines. Comparative transcriptome analysis identified 4204 differentially expressed genes (DEGs) between WT and PtrPIP2:4 overexpression plants. Transcriptomic analysis revealed that genes associated with auxin-related and flavonoid biosynthesis were significantly enriched. RT-qPCR results showed that the transcription levels of nine auxin-related genes (i.e., PtrARF, PtrIAA, PtrGH3 and PtrPIN) were significantly upregulated, while the transcription levels of five flavonoid synthesis genes (i.e., PtrDFR, PtrANS, PtrANR and PtrLAR) were also significantly upregulated. Previous studies have implicated these genes in adventitious root formation. Collectively, these findings reveal that PtrPIP2:4 accelerates adventitious root emergence, promotes adventitious root elongation, and increases lateral root number while the total number of adventitious roots exhibited no significant difference in poplar, suggesting its potential utility in improving tree propagation and breeding strategies.