Rehydration Compensation of Winter Wheat Is Mediated by Hormone Metabolism and De-Peroxidative Activities Under Field Conditions

Abstract

Water deficit and rehydration frequently occur during wheat cultivation. Previous investigations focused on the water deficit and many drought-responsive genes have been identified in winter wheat. However, the hormone-related metabolic responses and de-peroxidative activities associated with rehydration are largely unknown. In this study, leaves of two winter wheat cultivars, "Hengguan35" (HG, drought-tolerant cultivar) and "Shinong086" (SN, drought-sensitive cultivar), were used to investigate water deficit and the post-rehydration process. Rehydration significantly promoted wheat growth and postponed spike development. Quantifications of antioxidant enzymes, osmotic stress-related substances, and phytohormones revealed that rehydration alleviated the peroxidation and osmotic stress caused by water deficit in both cultivars. The wheat cultivar HG showed a better rehydration-compensation phenotype than SN. Phytohormones, including abscisic acid, gibberellin (GA), jasmonic acid (JA), and salicylic acid (SA), were detected using high-performance liquid chromatography and shown to be responsible for the rehydration process. A transcriptome analysis showed that differentially expressed genes related to rehydration were enriched in hormone metabolism- and de-peroxidative stress-related pathways. Suppression of genes associated with abscisic acid signaling transduction were much stronger in HG than in SN upon rehydration treatment. HG also kept a more balanced expression of genes involved in reactive oxygen species pathway than SN. In conclusion, we clarified the hormonal changes and transcriptional profiles of drought-resistant and -sensitive winter wheat cultivars in response to drought and rehydration, and we provided insights into the molecular processes involved in rehydration compensation.

Keywords: de-peroxidative stress; drought stress; hormone metabolism; rehydration compensation; transcriptomic; wheat.

FIGURE 1

Schematic representation of rehydration experimental design. (A) Rain shelter for field experiments. (B) Timeline for rehydration treatment and sample collection. (C) Profile of the relative soil-water content (RSWC) during different rehydration stages. Scale bar represents soil moisture content in percentage. R, rehydrated plants; D, plants under continuous drought stress.

FIGURE 2

The drought-tolerant wheat variety “Hengguan35” (HG) showed better rehydration-compensation phenotypes than the drought-sensitive wheat variety “Shinong086” (SN). (A) Plant morphology of HG and SN at 15 dpr. “*, **” indicate significant difference at 0.05 level. **P < 0.01; *P < 0.05. (B) Plant height was measured at 15 dpr. (C) Spikes were isolated and observed using a microscope at 1, 8, and 15 dpr. R, rehydrated plants; D, plants under continuous drought stress.

FIGURE 3

Physiological activities in HG and SN upon rehydration and continuous drought stress. The activity levels of SOD, POD, CAT, and APX in both HG and SN at 0, 1, 8, and 15 dpr were measured. The dynamic changes in contents of MDA, Pro, soluble protein, and soluble sugars in these samples were also monitored.

FIGURE 4

The contents of phytohormones in HG and SN upon rehydration and continuous drought stress were evaluated using HPLC. The concentrations of ABA, IAA, GA, JA, and SA in both HG and SN leaves at 0, 1, 8, and 15 dpr were quantified.

FIGURE 5

Transcriptome responses of winter wheat upon rehydration and continuous drought stress. (A) A principal component analysis for the overall gene expression levels in all the sequenced RNA libraries was conducted to evaluate the correlations among different samples. (B) Upset diagrams showing the DEGs at 1, 8, and 15 dpr. The lines between the two points represent the specific expressed genes between the samples, and the length of the columns represent the number of genes. (C) Venn diagram showing numbers of rehydration-drought shared, rehydration-specific, and drought-specific DEGs.

FIGURE 6

GO and KEGG annotations of the rehydration-drought shared, rehydration-specific, and drought-specific DEGs. Enrichment of GO annotations (A) and KEGG pathways (B) in rehydration-drought shared, rehydration-specific, and drought-specific DEGs were summarized.

FIGURE 7

Expression profiles of DEGs involved in plant hormone pathways. The expression profiles of transcripts (A) involved in hormone signal transduction pathways (B) were generated using their FPKM values.

FIGURE 8

Expression profiles of DEGs involved in ROS-related pathways. The expression levels of transcripts (A) in antioxidative and biosynthetic pathways (B) were generated using their FPKM values.

FIGURE 9

The expression profiles of six randomly selected DEGs were validated by qRT-PCR assay. (A) The expression patterns of six randomly selected DEGs were generated using both qRT-PCR data and FPKM values. The relative transcript abundances were expressed relative to that of the internal reference TaActin following the 2^–ΔΔCt method. FPKM values of these DEGs were collected from the transcriptome database. (B) Correlation analysis on the overall expression levels of six selected DEGs between RNA-seq and qRT-PCR. Log2FC values of RNA-seq data (x-axis) were plotted against log2FC values of qRT-PCR data (y-axis). R, rehydrated plants; D, plants under continuous drought stress.