Integrating transcriptome and metabolome to explore the growth-promoting mechanisms of GABA in blueberry plantlets

Abstract

Tissue culture technology is the main method for the commercial propagation of blueberry plants, but blueberry plantlets grow slowly and have long growth cycles under in vitro propagation, resulting in low propagation efficiency. In addition, the long culturing time can also result in reduced nutrient content in the culture medium, and the accumulation of toxic and harmful substances that can lead to weak growth for the plantlets or browning and vitrification, which ultimately can seriously reduce the quality of the plantlets. Gamma-aminobutyric acid (GABA) is a four-carbon non-protein amino acid that can improve plant resistance to various stresses and promote plant growth, but the effects of its application and mechanism in tissue culture are still unclear. In this study, the effects of GABA on the growth of in vitro blueberry plantlets were analyzed following the treatment of the plantlets with GABA. In addition, the GABA-treated plantlets were also subjected to a comparative transcriptomic and metabolomic analysis. The exogenous application of GABA significantly promoted growth and improved the quality of the blueberry plantlets. In total, 2,626 differentially expressed genes (DEGs) and 377 differentially accumulated metabolites (DAMs) were detected by comparison of the control and GABA-treated plantlets. Most of the DEGs and DAMs were involved in carbohydrate metabolism and biosynthesis of secondary metabolites. The comprehensive analysis results indicated that GABA may promote the growth of blueberry plantlets by promoting carbon metabolism and nitrogen assimilation, as well as increasing the accumulation of secondary metabolites such as flavonoids, steroids and terpenes.

Keywords: blueberry plantlets; gamma-aminobutyric acid; metabolome; tissue culture; transcriptome.

Figure 1

Effects of GABA on the morphology and growth in Vaccinium plantlets in vitro. (A) Morphology characteristics; (B) plant height; (C) fresh weight; (D) multiplication ratio. CK, control; GB, 0.5 g·L^-1 GABA. Data are shown as the mean ± SEM. Significance of control vs 0.5 g·L^-1 GABA is indicated by one (P < 0.05) or two (P < 0.01) asterisks.

Figure 2

PCA (A) and OPLS-DA (B) analysis diagram of metabolites in Vaccinium plantlets in vitro samples.

Figure 3

Bubble diagram of differential metabolic pathway.

Figure 4

Differential expressed genes histogram.

Figure 5

KEGG pathway categories of differentially expressed genes.

Figure 6

Carbon and nitrogen metabolism map. The histogram in the diagram indicates the change of metabolite content, and the heat map indicates the change of gene expression. NRT, Nitrate Transporter; NPF, NRT/PTR; AMT, Aminomethyl Transferase; GOGAT, Glutamate Synthase; GS, Glutamine Synthetase; FBPase, Fructose 1, 6-bisphosptase; ADPGase, ADP-glucose Pyrophosphorylase; SSS, Soluble Starch Synthase; GBE, 1,4-alpha-glucan-branching Enzyme; Glu, Glutamate; Gln, Glutamine; Arg, Arginine; GSH, Glutathion; CA, Citric Acid; I-CIT, Isocitric acid; KGA, α-Ketoglutaric acid; SUC, Succinic acid; OAA, Oxalacetic acid; Asp, Aspartic acid; Lys, Lysine; FDP, Fructose1,6-diphosphate; F6P, Fructose 6 phosphate; G1P, Glucose 1-phosphate.

Figure 7

Effects of GABA on the contents of flavonoids (A), steroids and steroid derivatives (B) and prenol lipids (C) in Vaccinium plantlets in vitro.

Figure 8

The model of exogenous GABA improving the adaptability of plantlets in vitro to the adverse environment. SSS, Soluble Starch Synthase; GBE, 1,4-alpha-glucan-branching Enzyme; FBPase, Fructose 1, 6-bisphosptase; ADPGase, ADP-glucose Pyrophosphorylase; CesA, cellulose synthase; GS, Glutamine Synthetase; AMT, Aminomethyl Transferase; GOGAT, Glutamate Synthase; CA, Citric Acid; I-CIT, Isocitric acid; Arg, Arginine; Lys, Lysine; GSH, Glutathion; FUC, Fucose; CQA, Caffeoylquinic acid; AR, Arbutin.