Down‐regulation of GIGANTEA ‐ like genes increases plant growth and salt stress tolerance in poplar

Summary The flowering time regulator GIGANTEA ( GI ) connects networks involved in developmental stage transitions and environmental stress responses in Arabidopsis . However, little is known about the role of GI in growth, development and responses to environmental challenges in the perennial plant poplar. Here, we identified and functionally characterized three GI ‐like genes ( Pag GI a , Pag GI b and Pag GI c) from poplar ( Populus alba × Populus glandulosa ). Pag GI s are predominantly nuclear localized and their transcripts are rhythmically expressed, with a peak around zeitgeber time 12 under long‐day conditions. Overexpressing Pag GI s in wild‐type (WT) Arabidopsis induced early flowering and salt sensitivity, while overexpressing Pag GI s in the gi‐2 mutant completely or partially rescued its delayed flowering and enhanced salt tolerance phenotypes. Furthermore, the Pag GI s‐Pag SOS 2 complexes inhibited Pag SOS 2‐regulated phosphorylation of Pag SOS 1 in the absence of stress, whereas these inhibitions were eliminated due to the degradation of Pag GI s under salt stress. Down‐regulation of Pag GI s by RNA interference led to vigorous growth, higher biomass and enhanced salt stress tolerance in transgenic poplar plants. Taken together, these results indicate that several functions of Arabidopsis GI are conserved in its poplar orthologues, and they lay the foundation for developing new approaches to producing salt‐tolerant trees for sustainable development on marginal lands worldwide.