Metal tolerance proteins (MTPs) are plant divalent cation transporters that play important roles in plant metal tolerance and homeostasis. Poplar is an ideal candidate for the phytoremediation of heavy metals because of its numerous beneficial attributes. However, the definitive phylogeny and heavy metal transport mechanisms of the MTP family in poplar remain unknown. Here, 22 MTP genes in P. trichocarpa were identified and classified into three major clusters and seven groups according to phylogenetic relationships. An evolutionary analysis suggested that PtrMTP genes had undergone gene expansion through tandem or segmental duplication events. Moreover, all PtrMTPs were predicted to localize in the vacuole and/or cell membrane, and contained typical structural features of the MTP family, cation efflux domain. The temporal and spatial expression pattern analysis results indicated the involvement of PtrMTP genes in poplar developmental control. Under heavy metal stress, most of PtrMTP genes were induced by at least two metal ions in roots, stems or leaves. In addition, PtrMTP8.1, PtrMTP9 and PtrMTP10.4 displayed the ability of Mn transport in yeast cells, and PtrMTP6 could transport Co, Fe and Mn. These findings will provide an important foundation to elucidate the biological functions of PtrMTP genes, and especially their role in regulating heavy metal tolerance in poplar.

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Finding the adequate balance between wood formation and abiotic stress resistance is still an important challenge for industrial woody crops. In this study, PeNAC122, a member of the NAC transcription factor (TF) family highly expressed in xylem, was cloned from Populus euphratica. Tissue expression and β‐glucuronidase (GUS) staining showed that PeNAC122 was exclusively expressed in phloem fiber and secondary xylem of stems. Subcellular and yeast transactivation assays confirmed that PeNAC122 protein existed in the nucleus and did not have transcriptional activation and inhibitory activity. Overexpression of PeNAC122 poplar lines exhibited reduced plant height, thickened xylem, and accumulated lignin content in stems, and also upregulates the expression of secondary cell wall biosynthetic genes. Moreover, overexpression of PeNAC122 lines displayed more tolerance to PEG6000‐induced osmotic stress, with stronger photosynthetic performance, higher antioxidant enzyme activity, and less accumulation of reactive oxygen species in leaves, and higher expression levels of stress response genes DREB2A, RD29, and NCED3. These results indicate that PeNAC122 plays a crucial role in wood formation and abiotic stress tolerance, which, in addition to potential use in improving wood quality, provides further insight into the role of NAC family TFs in balancing wood development and abiotic stress resistance.