PtmiR169o plays a positive role in regulating drought tolerance and growth by targeting the PtNF-YA6 gene in poplar

miR169 and its target NF-YAs are involved in developmental and environmental stress responses in plants. However, their functions in woody plants have rarely been reported. Here, a miR169 family member, PtmiR169o, and its target PtNF-YA6 gene from Populus trichocarpa were characterized. The expression of PtmiR169o was up-regulated under drought, NaCl and ABA treatments. The overexpression of PtmiR169o in poplar significantly improved the photosynthetic rate and reduced the water loss rate of leaves under drought stress, resulting in enhanced drought resistance. PtmiR169o transgenic lines also exhibited both shoot and root growth under normal growth conditions. PtNF-YA2 and PtNF-YA6, as the target genes of PtmiR169o, were confirmed by psRNATarget prediction, real-time PCR, tobacco co-injection, and 5ʹ RACE analysis. Moreover, the overexpression of PtNF-YA6 poplar resulted in growth reduction and increased sensitivity to drought stress, which is consistent with the functional characteristics of miRNAs and their target genes. In conclusion, the results of this study indicate that PtmiR169o regulates plant growth and drought resistance by targeting the PtNF-YA6 gene. Thus, our findings lay the foundation for developing new approaches to producing drought-tolerant trees for sustainable development on marginal land worldwide.