Transcriptional Profiles of Drought-Related Genes in Modulating Metabolic Processes and Antioxidant Defenses in Lolium multiflorum

Abstract

Drought is a major environmental stress that limits growth and development of cool-season annual grasses. Drought transcriptional profiles of resistant and susceptible lines were studied to understand the molecular mechanisms of drought tolerance in annual ryegrass (Lolium multiflorum L.). A total of 4718 genes exhibited significantly differential expression in two L. multiflorum lines. Additionally, up-regulated genes associated with drought response in the resistant lines were compared with susceptible lines. Gene ontology enrichment and pathway analyses revealed that genes partially encoding drought-responsive proteins as key regulators were significantly involved in carbon metabolism, lipid metabolism, and signal transduction. Comparable gene expression was used to identify the genes that contribute to the high drought tolerance in resistant lines of annual ryegrass. Moreover, we proposed the hypothesis that short-term drought have a beneficial effect on oxidation stress, which may be ascribed to a direct effect on the drought tolerance of annual ryegrass. Evidence suggests that some of the genes encoding antioxidants (HPTs, GGT, AP, 6-PGD, and G6PDH) function as antioxidant in lipid metabolism and signal transduction pathways, which have indispensable and promoting roles in drought resistance. This study provides the first transcriptome data on the induction of drought-related gene expression in annual ryegrass, especially via modulation of metabolic homeostasis, signal transduction, and antioxidant defenses to improve drought tolerance response to short-term drought stress.

Keywords: Lolium multiflorum L; antioxidant defense; differentially expressed genes; drought tolerance; metabolic processes.

Figure 1

The physiological indexes of L. multiflorum were measured after drought treatments. Leaf transpiration rate (A) and leaf water potential (B) in drought-resistant and drought-susceptible plants after 0, 1, and 2 h of treatment (A,B). Malondialdehvde content (C) and H₂O₂ concentration (D) of 20-day-old annual ryegrass lines with drought stress for 0, 1, and 2 h (C,D). The enzymatic activities of catalases (E), superoxide dismutase (F), dehydroascorbate reductase (G), and monodehydroasorbate reductase (H) of two L. multiflorum lines after different drought treatments (E–G). Bars with different letters above the columns of figures indicate significant differences (P < 0.05) between different time points.

Figure 2

Statistics of up- and down-regulated genes between the two L. multiflorum lines (A); The expression level of DEGs in resistant and susceptible lines exposed to drought (B–C). The upper with red regions reveal those genes with significantly up-regulated expression. Similarly, the lower with green dots shows the down-regulated genes and the blue dots represent the region with no DGEs.

Figure 3

Comparison of differentially expressed genes of the Gene Ontology (GO) analysis including biological process (A) and molecular functions (B) in two annual ryegrass lines subjected to drought stress for 1 and 2 h. And the percent of DEGs involved in metabolic processes in resistant and susceptible lines is shown in (C,D).

Figure 4

Scatter diagrams of different changing trends of DEGs in two L. multiflorum lines by GO enrichment analysis after drought treatment for 1 and 2 h. The GO terms included response to osmotic stress and response to a water stimulus (A), response to an organic substance and response to an oxygen-containing compound (B), and response to lipid and nucleobase-containing compound biosynthetic process (C).

Figure 5

Comparison of the different expression trends among 15 genes using both qRT-PCR results and RNA-Seq data in the resistant lines (A) and susceptible lines (B) of L. multiflorum.

Figure 6

Effects of drought stress on the expression of genes associated with glycolysis and gluconeogenesis (A), starch and sucrose metabolism (B), glycerophospholipid metabolism (C), and signal transduction (D) in resistant lines. The red arrow indicates significantly up-regulated expression.