Biochemical and Transcriptional Regulation of Membrane Lipid Metabolism in Maize Leaves under Low Temperature

Abstract

Membrane lipid modulation is one of the major strategies plants have developed for cold acclimation. In this study, a combined lipidomic and transcriptomic analysis was conducted, and the changes in glycerolipids contents and species, and transcriptional regulation of lipid metabolism in maize leaves under low temperature treatment (5°C) were investigated. The lipidomic analysis showed an increase in the phospholipid phosphatidic acid (PA) and a decrease in phosphatidylcholine (PC). And an increase in digalactosyldiacylglycerol and a decrease in monogalactosyldiacylglycerol of the galactolipid class. The results implied an enhanced turnover of PC to PA to serve as precursors for galactolipid synthesis under following low temperature treatment. The analysis of changes in abundance of various lipid molecular species suggested major alterations of different pathways of plastidic lipids synthesis in maize under cold treatment. The synchronous transcriptomic analysis revealed that genes involved in phospholipid and galactolipid synthesis pathways were significantly up-regulated, and a comprehensive gene-metabolite network was generated illustrating activated membrane lipids adjustment in maize leaves following cold treatment. This study will help to understand the regulation of glycerolipids metabolism at both biochemical and molecular biological levels in 18:3 plants and to decipher the roles played by lipid remodeling in cold response in major field crop maize.

Keywords: RNA-Seq; lipid metabolism; lipidome profiling; low temperature; maize.

FIGURE 1

Changes of glycerolipids species in maize leaves under low temperature (5°C) in comparison to room temperature (22°C). Values (mol %) are means 5 ± standard deviation (SD) (n = 5). MGDG, monogalactosyldiacylglycerol; DGDG, digalactosyldiacylglycerol; SQDG, sulfoquinovosyldiacylglycerol; PG, phosphatidylglycerol; PC, phosphatidylcholine; PE, phosphatidylethanolamine; LPG, Lyso-PC; LPC, Lyso-PC; LPA, Lyso-PC. “^∗” indicated that the value was significantly different from the control (P < 0.05).

FIGURE 2

Changes in diacyl lipid molecular species of major phospholipids and plastidic glycerolipids in maize leaves under low temperature (5°C) in comparison to room temperature (22°C). (A) Major phospholipids, PI, phosphatidylinositol; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PA, phosphatidic acid. (B) Major plastidic glycerolipids, PG, phosphatidylglycerol; MGDG, monogalactosyldiacylglycerol; DGDG, digalactosyldiacylglycerol; SQDG, sulfoquinovosyldiacylglycerol. Values (mol %) are means 5 ± standard deviation (SD) (n = 5). “^∗” indicated that the value was significantly different from the control (P < 0.05). More detailed MGDG and DGDG molecular species as shown in Supplementary Figure S3.

FIGURE 3

Functional categorization of lipid-related genes from transcriptome of maize leaves (5°C vs. 22°C). Genes involved in lipid metabolism were compiled from the Arabidopsis lipid gene database (Beisson et al., 2003) and categorized based on different pathways. Pink columns represent down-regulated genes, and blue columns represent up-regulated genes. In each category, the light colored column represents the total differentially expressed genes (DEG), and the dark colored column represents the significantly differentially expressed genes (DEG, Log2FC ≥1.5 or ≤–1.5). The number of the genes in each category were displayed in the x-axis (the ones on the upper x-axis indicate the DEG, Log2FC ≥1.5 or ≤–1.5).

FIGURE 4

A schematic diagram of gene-metabolite network demonstrates lipid metabolism in maize under low temperature stress. The glycerolipids synthesis pathways were depicted and the involving genes and lipid melatolites were symbolized. The relative change of lipid molecular species [(5°C mol % –22°C mol %)/22°C mol %] and the relative expression levels of selected genes [Log2FC ≥1.5 or ≤–1.5, (5°C vs. 22°C)] were marked as heat-map icons. The red arrows represents activated steps by cold. ER, endoplasmic reticulum; OE, outer envelope; IE, inner envelope; Chl, chloroplast. The map is based on (Ohlrogge and Browse, 1995; Benning, 2009; DeBolt et al., 2009; Shen et al., 2010; Narayanan et al., 2016a).

FIGURE 5

The proposed interaction and intermediates exchange between phospholipids pathway and galactolipids pathway in maize under low temperature stress. The de novo assembly of PA and DAG in endoplasmic reticulum and plastid produced different PA and DAG pools (the ER localized were marked as bbb172, and plastid localized were marked as bbb174) and PA and DAG generated from PC hydrolysis by phospholipases form a separated PA and DAG pool (marked as bbb173). A, B, C represents the proposed routes for the lipids trafficking between ER and chloroplast. ER, endoplasmic reticulum; OE, outer envelope; IE, inner envelope.