Transcriptomic and metabolomic effects of exogenous ABA application on tobacco seedling growth

Abscisic acid (ABA) research has focused on improving plant resistance under stress; however, the effects of exogenous ABA application in plants under non-stress conditions have not been thoroughly analyzed. Here, we explored the regulatory effects of exogenous ABA application on the growth of a model plant, tobacco, in an environment with no stressors by spraying leaves at the seedling stage. At the same time, as an important cash crop in the world, ABA can improve the growth ability of tobacco seedling stage and have a positive impact on the later growth.We found a significant increase in tobacco biomass under a 0.5 mg/L ABA treatment. Chlorophyll fluorescence parameters, including PIabs, Fm, Phi (Eo), Phi (Po), Sm, and N in the ABA group increased in different degrees compared with the control (CK group). Ultrastructure observation of tobacco leaves showed that chloroplast, plasmid, and mitochondria ultrastructure were significantly different from those in the CK group. qRT-PCR confirmed the reliability of the transcriptome results. ABA may increase the biomass of tobacco by affecting the expression of receptor genes of plant hormones such as auxin and gibberellin, as well as the synthesis of alkaloids and metabolism of amino acids such as phenylalanine. We found that genes expressed in related resistance pathways, such as CNGCs and CDPK, were down-regulated, suggesting that they may affect the tobacco plants’ ability to defend itself against pathogens. These preliminary findings provide a reference for further revealing the mechanism of exogenous ABA in regulating plant growth under non-stress environments.