MtCIR2 negatively regulates seed germination to salt stress by disrupting metabolisms and signaling of abscisic acid and gibberellins

Emerging evidence indicates that long non-coding RNAs (lncRNAs) play a regulatory role in plant response to environmental stresses. Seed germination is a complex physiological process modulated by many environmental and phytohormonal cues. However, how lncRNAs and phytohormones interactively regulate the response of seed germination to salt stress remain largely unknown. Here, we functionally characterized a salt-responsive lncRNA from legume species Medicago truncatula, referred to as MtCIR2, in response to salt stress during seed germination by heterologously expressing MtCIR2 in Arabidopsis in which none such homologous sequence was detected. Expressing MtCIR2 in Arabidopsis rendered the seed germination more sensitive to salt stress. We further evaluated whether and how abscisic acid (ABA) and gibberellin (GA) were involved in the MtCIR2-mediated seed germination in response to salt stress. We found that expression of MtCIR2 led to an increase in endogenous ABA concentration and a decrease in overall GA concentration due to enhanced expression of ABA catabolic gene CYP707A2 and suppressed expression of the genes of GA20ox1, GA20ox2, and GA20ox5 involved in GA synthesis under salt stress, respectively. The MtCIR2-dependent enhanced endogenous ABA and reduced endogenous GA concentrations in seeds resulted in greater suppression of seed germination in transgenic seeds than in wild-type seeds when exposed to salt stress. These findings highlight a regulatory role of lncRNAs in response to salt stress during seed germination.