Roles of γ-aminobutyric acid on salinity-responsive genes at transcriptomic level in poplar: involving in abscisic acid and ethylene-signalling pathways.

Abstract

γ-Aminobutyric acid (GABA) affected ABA and ethylene metabolic genes and signal components in salt-treated poplar, indicating its potential role in signal pathways of ABA and ethylene during salt stress. GABA is a small signalling molecule that accumulates rapidly in plants exposed to various stresses. However, the relationship between GABA and other signalling molecules, such as hormones, remains unclear. Here, in the poplar woody plant under 200-mM NaCl conditions, the application of low (0.25mM) and high (10mM) exogenous GABA, compared to 0mM, affected the accumulation of hydrogen peroxide and hormones, including ABA and ethylene, in different manners. Transcriptomic analysis demonstrated that 1025 differentially expressed genes (DEGs; |log2Ratio| ≥ 1.5) were widely affected by exogenous GABA under salt stress. A clustering analysis revealed that GABA could rescue or promote the effects of salt stress on gene expression. Among them, 146 genes involved in six hormone-signalling pathways were enriched, including 22 ABA- and 50 ethylene-related genes. Quantitative expression of selected genes involved in hormone-related pathways showed that ABA metabolic genes (ABAG, ABAH2, and ABAH4), ethylene biosynthetic genes (ACO1, ACO2, ACO5, ACOH1, ACS1, and ACS7) and receptor genes (PYL1, PYL2, PYL4, and PYL6) were regulated by exogenous GABA, even at a 0.1mM level. The production of ABA was negatively correlated with ABAH expression levels at different GABA concentrations. The increase of endogenous GABA, resulting from inhibitor (succinyl phosphonate) of α-ketoglutarate dehydrogenase, affected the PYLs levels. Thus, GABA may be involved in ABA- and ethylene-signalling pathways. Our data provide a better understanding of GABA's roles in the plant responses to environmental stresses.