LAUSR

BACKGROUND AND AIMS In our previous study, interspecific grafting of Populus cathayana (C) onto Populus deltoides (D) significantly improved the drought tolerance in grafted plants. However, whether this advantage could be maintained under salt stress condition and the relative underlying mechanism are unclear. METHODS Physiological, lncRNA-seq and metabolic analyses were performed to illuminate the mechanism governing the different responses to salt stress between C/D (C grafted onto D) and D/C (D grafted onto C) plants. KEY RESULTS Salt stress reduced the growth and biomass of all the grafted plants, with C/D plants showed stronger salt tolerance than did D/C plants, as evidenced by its greater biomass production and sugar content, less leaf cell damage, and better ion homeostasis. More lncRNAs, mRNAs and metabolites related to carbohydrate metabolism were detected in D/C than in C/D plants. Genes related to structural and non-structural carbohydrates metabolism were respectively up- and down-regulated in C/D and D/C plants, and the changes of citramalic acid, sorbitol and pyruvic acid contents were strongly supported by their different carbohydrate metabolisms. In addition, lncRNAs MSTRG.102 and MSTRG.4684, as well as their target genes involved in carbohydrate metabolism, were less significantly down-regulated in C/D than in D/C plants. Furthermore, correlation analysis revealed that MSTRG.7877 and MSTRG.20540 might be the key lncRNAs in the grafted plants in response to salt stress. CONCLUSIONS Our study demonstrates that through affecting the accumulation and metabolism of carbohydrates, different expression and content of multiple lncRNAs, mRNAs and metabolites, associated with structural and non-structural carbohydrates, led to different growth and salt tolerance between C/D and D/C plants. The improved growth and salt tolerance in C/D plants was closely associated with the altered structural and non-structural carbohydrate accumulation and metabolism.