Acyl-CoA-binding protein (ACBP) genes involvement in response to abiotic stress and exogenous hormone application in barley (Hordeum vulgare L.)

Abstract

Background: Acyl-CoA-Binding proteins (ACBPs) function as coenzyme A transporters and play important roles in regulating plant growth and development in response to abiotic stress and phytohormones, as well as in membrane repair. To date, the ACBP family has not been a comprehensively characterized in barley (Hordeum vulgare L.).

Results: Eight ACBP genes were identified in the barley genome and named as HvACBP1-8. The analysis of the proteins structure and promoter elements of HvACBP suggested its potential functions in plant growth, development, and stress response. These HvACBPs are expressed in specific tissues and organs following induction by abiotic stressors such as drought, salinity, UV-B exposure, temperature extremes, and exposure to exogenous phytohormones. The HvACBP7 and HvACBP8 amino acid sequences were conserved during the domestication of Tibetan Qingke barley.

Conclusions: Acyl-CoA-binding proteins may play important roles in barley growth and environmental adaptation. This study provides foundation for further analyses of the biological functions of HvACBPs in the barley stress response.

Keywords: Acyl-CoA-binding protein (ACBP); Barley stress response; Gene expression pattern.

Fig. 1

Phylogenetic analysis and collinearity analyses of ACBP in Arabidopsis thaliana, Glycine max, Oryza sativa, Triticum aestivum, Zea mays, Sorghum bicolor, and Hordeum vulgare (a) Phylogenetic tree of ACBP genes. The full-length sequence of the ACBP proteins was used for sequence alignment and phylogenetic analysis. Blocks of different colors indicate distinct subgroups, whereas in same color are indicated within a subgroup. (b) Collinear ACBP blocks in barley and related species. Gray lines in the background indicate collinear blocks within Hordeum vulgare and other plant genomes; collinear ACBP gene pairs are colored in red

Fig. 2

Maximum likelihood phylogenetic structure and motifs of acyl-CoA-binding protein (ACBP) genes in Hordeum vulgare L. (a) Phylogenetic tree and HvACBP subfamilies, further divided into four groups. (b) HvACBP exon–intron organization. (c) ACBP motifs. (d) Ankyrin domains are conserved in the ANK-ACBP subfamily and the Kelch domain is conserved in the Kelch-ACBP subfamily

Fig. 3

Predicted secondary and tertiary structure of acyl-CoA-binding proteins (ACBPs) in Hordeum vulgare L. (a) HvACBP secondary structure. Orange block: α-helical conformation. Blue: random- coil structure. (b) HvACBP tertiary structure. Blue block: α-helical conformation. Green: β-fold conformation. White line: random-coil structure

Fig. 4

Maximum likelihood phylogenetic trees and prediction of cis-acting elements in the acyl-CoA-binding protein gene (ACBP) promoters of Hordeum vulgare L. Two-kilobase pair promoter sequences were used to analyze hormone-related cis-elements, plant growth and development-related cis-elements, and stress-related elements. Different types of cis-elements are indicated by different colored symbols adjacent to their respective promoter

Fig. 5

Relative expression of acyl-CoA-binding protein genes (ACBPs) in different tissues of Hordeum vulgare L. Heat maps reflect the fragments per kilobase of transcript per million mapped fragments (FPKM) of HvACBPs. The color gradient from red to blue indicates high to low expression. ETI: seedlings were grown to 10 days after planting (dap) in the dark to isolate etiolated leaves. LEA: leaf tissue, 17 dap. ROO1: root tissue, 17 dap. ROO2: root tissue, 28 dap. EPI: epidermal strips were obtained from plant leaf tissue at 28 dap. NOD: third stem internode, 42 dap. SEN: senescing leaf, 56 dap. INF1: whole developing inflorescence tissue was sampled at 30 dap. INF2: whole developing inflorescence tissue, 50 dap. RAC: rachis, 35 dap. LOD: lodicule, 42 dap. LEM: lemma. PAL: palea. CAR5: development grain, 5 days post-anthesis(dpa). CAR15: development grain, 15 dpa. EMB: embryonic tissue, 4 d after germination of mature grain in Petri plates in the dark in the laboratory

Fig. 6

Acyl-CoA-binding protein gene (ACBP) expression in Hordeum vulgare L. under hormone treatment and abiotic stress.Stress was induced by hormone treatment with indoel-3-acetic acid (IAA) at 0.15 µmol/L or abscisic acid (ABA) at 100 µmol/L or methyl jasmonate (MeJA) at 100 µmol/L, and ACBP expression was measured after 1, 3, 6, 12, and 24 h. Responses to abiotic stressors were measured 1, 3, 6, 12, and 24 h after treatment with 200 mM NaCl, 20% polyethylene glycol (PEG6000), or 30 µW/cm² UV radiation (growth lamp was turned off after 12 h of UV treatment, and no UV treatment was provided after 12 h). Cold and heat stress were applied via treatment at 4 °C and 42 °C, respectively. The expression levels of genes in the control were defined as “1”. The values are presented as the means of three replicates. “*” as significant at P ≤ 0.05, “**” as significant at P ≤ 0.01, “***” as significant at P ≤ 0.001

Fig. 7

HvACBP7 haplotype analysis. (a) Single-nucleotide polymorphisms (SNPs) were identified for haplotype analysis. Light-green rectangles: exons; straight lines: introns; SNPs in the promoter and coding sequence are shown in the upper table. Indels are represented by i1–7. (b) Proportions of each barley resource having each haplotype, with haplotype network analysis