Magnesium Deficiency Induced Global Transcriptome Change in Citrus sinensis Leaves Revealed by RNA-Seq

Abstract

Magnesium (Mg) deficiency is one of the major constraining factors that limit the yield and quality of agricultural products. Uniform seedlings of the Citrus sinensis were irrigated with Mg deficient (0 mM MgSO₄) and Mg sufficient (1 mM MgSO₄) nutrient solutions for 16 weeks. CO₂ assimilation, starch, soluble carbohydrates, TBARS content and H₂O₂ production were measured. Transcriptomic analysis of C. sinensis leaves was performed by Illumina sequencing. Our results showed that Mg deficiency decreased CO₂ assimilation, but increased starch, sucrose, TBARS content and H₂O₂ production in C. sinensis leaves. A total of 4864 genes showed differential expression in response to Mg deficiency revealed by RNA-Seq and the transcriptomic data were further validated by real-time quantitative PCR (RT-qPCR). Gene ontology (GO) enrichment analysis indicated that the mechanisms underlying Mg deficiency tolerance in C. sinensis may be attributed to the following aspects: a) enhanced microtubule-based movement and cell cycle regulation; b) elevated signal transduction in response to biotic and abiotic stimuli; c) alteration of biological processes by tightly controlling phosphorylation especially protein phosphorylation; d) down-regulation of light harvesting and photosynthesis due to the accumulation of carbohydrates; e) up-regulation of cell wall remodeling and antioxidant system. Our results provide a comprehensive insight into the transcriptomic profile of key components involved in the Mg deficiency tolerance in C. sinensis and enrich our understanding of the molecular mechanisms by which plants adapted to a Mg deficient condition.

Keywords: Citrus sinensis; Mg deficiency; cellular transport; signal transduction; transcriptome.

Figure 1

Symptom of Mg deficiency in C. sinensis leaf.

Figure 2

Effects of Mg deficiency on plant dry weight (DW; root, (A); stem, (B); shoot, (C)) and Mg content (root, (D); stem, (E); leaf, (F)) in C. sinensis seedlings. Bars represent means ±SD (n = 5 for Mg content or 10 for plant DW). Difference among the treatments was analyzed by student’s t-test. Different letters indicate a significant difference at p < 0.05.

Figure 3

Effects of Mg deficiency on CO₂ assimilation (A), intercellular CO₂ (B), maximum quantum yield of primary photochemistry (Fv/Fm) (C), electron transport flux per reaction center at t = 0 (ET_o/RC) (D), minimum fluorescence (F_o) (E), leaf starch (F), sucrose (G), H₂O₂ production (H), TBARS (I) and lignin (J) content in C. sinensis. Bars represent means ±SD (n = 4). Difference among the treatments was analyzed by student’s t-test. Different letters indicate a significant difference at p < 0.05.

Figure 4

Gene ontology (GO) term enrichment analysis of differentially expressed genes (DEGs) in C. sinensis leaves. * Asterisk means DEGs were significantly enriched in this GO term.

Figure 5

Relative expression levels of ten DEGs under Mg deficiency in C. sinensis leaves. Cs5g07230: cytochrome P450; Cs5g31590: tRNA delta (2)-isopentenyl pyrophosphate transferase; Cs6g15360: dehydration-responsive element-binding protein 1B; Cs5g29830: MYB4; Cs5g29870: ethylene-responsive transcription factor 1B; Cs3g02300: helicase SEN1; Cs2g26250: calcium-transporting ATPase 2; Cs4g05760: WRKY50; Cs3g08290: isoflavone reductase; Cs8g04290: transposon protein. Bars represent means ±SD (n = 3). Difference among the treatments was analyzed by student’s t-test. Different letters indicate a significant difference at p < 0.05.