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. 2017 Jun 26:8:1104.
doi: 10.3389/fpls.2017.01104. eCollection 2017.

Physiological and Transcriptional Changes of Three Citrus Rootstock Seedlings under Iron Deficiency

Lina Fu  1   2 , Qingqing Zhu  1   2 , Yinya Sun  1   2 , Wei Du  1   2 , Zhiyong Pan  1   2 , Shu'ang Peng  1   2
Affiliations

Physiological and Transcriptional Changes of Three Citrus Rootstock Seedlings under Iron Deficiency

Lina Fu et al. Front Plant Sci. .

Abstract

Iron is an essential micronutrient for plants, and plants have evolved adaptive mechanisms to improve iron acquisition from soils. Grafting on iron deficiency-tolerant rootstock is an effective strategy to prevent iron deficiency-chlorosis in fruit-tree crops. To determine the mechanisms underlying iron uptake in iron deficiency, two iron deficiency-tolerant citrus rootstocks, Zhique (ZQ) and Xiangcheng (XC), as well as iron deficiency-sensitive rootstock trifoliate orange (TO) seedlings were studied. Plants were grown in hydroponics system for 100 days, having 50 μM iron (control) and 0 μM iron (iron deficiency) nutrient solution. Under iron deficiency, more obvious visual symptoms of iron chlorosis were observed in the leaves of TO, whereas slight symptoms were observed in ZQ and XC. This was further supported by the lower chlorophyll concentration in the leaves of TO than in leaves of ZQ and XC. Ferrous iron showed no differences among the three citrus rootstock roots, whereas ferrous iron was significantly higher in leaves of ZQ and XC than TO. The specific iron absorption rate and leaf iron proportion were significantly higher in ZQ and XC than in TO, suggesting the iron deficiency tolerance can be explained by increased iron uptake in roots of ZQ and XC, allowed by subsequent translocation to shoots. In transcriptome analysis, 29, 298, and 500 differentially expressed genes (DEGs) in response to iron deficiency were identified in ZQ, XC, and TO, respectively (Fold change ≥ 2 and Probability ≥ 0.8 were used as thresholds to identify DEGs). A Gene Ontology analysis suggested that several genotype-specific biological processes are involved in response to iron deficiency. Genes associated with cell wall biosynthesis, ethylene and abscisic acid signal transduction pathways were involved in iron deficiency responses in citrus rootstocks. The results of this study provide a basis for future analyses of the physiological and molecular mechanisms of the tolerance of different citrus rootstocks to iron deficiency.

Keywords: citrus rootstocks; gene expression regulation; iron concentration; iron deficiency; transcriptome analysis.

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Figures

FIGURE 1
FIGURE 1
Difference in leaf growth parameters of Zhique (ZQ), Xiangcheng (XC), and trifoliate orange (TO) grown in control and iron deficiency nutrient solution for 100 days. (A) Leaf morphology in ZQ, XC, and TO. (B,C) Chlorophyll concentration of leaves in ZQ, XC, and TO. (D,E) Leaf dry weight and leaf area of leaves in ZQ, XC, and TO. Letters (a, b, and c) indicate significant differences within samples via Duncan’s multiple range test P < 0.05 (Means ± SEM, n = 3).
FIGURE 2
FIGURE 2
Root growth parameters of ZQ, XC, and TO grown in control and iron deficiency nutrient solution for 100 days. (A) Root morphology in ZQ, XC, and TO. (B–E) Root growth parameters in ZQ, XC and TO. Letters (a, b, and c) indicate significant differences within samples via Duncan’s multiple range test P < 0.05 (Means ± SEM, n = 3).
FIGURE 3
FIGURE 3
Total Fe and ferrous Fe concentrations in ZQ, XC, and TO grown in control and iron deficiency nutrient solution for 100 days. (A–C) Total iron concentrations in ZQ, XC, and TO. (D–F) Ferrous iron concentrations in ZQ, XC, and TO. Data are shown as means ± SEM (n = 3). Letters (a, b, and c) indicate significant differences within samples via Duncan’s multiple range test P < 0.05 (Means ± SEM, n = 3).
FIGURE 4
FIGURE 4
Fe content per plant and specific Fe absorption rate in ZQ, XC, and TO grown in control and iron deficiency nutrient solution for 100 days. (A) Fe content per plant in ZQ, XC, and TO. (B) Specific Fe absorption rate in ZQ, XC, and TO. Letters (a, b, and c) indicate significant differences within samples via Duncan’s multiple range test P < 0.05 (Means ± SEM, n = 3).
FIGURE 5
FIGURE 5
Fe distribution in roots, stems and leaves of ZQ, XC, and TO grown in control and iron deficiency nutrient solution for 100 days. (A) Fe distribution in roots, stems, and leaves of ZQ, XC, and TO under control. (B) Fe distribution in roots, stems and leaves of ZQ, XC, and TO under iron deficiency. Letters (a, b, and c) indicate significant differences within samples via Duncan’s multiple range test P < 0.05 (Means ± SEM, n = 3).
FIGURE 6
FIGURE 6
Differentially Expressed Genes in roots of citrus rootstocks in 24 h of control and iron deficiency conditions. (A) Numbers of differentially expressed genes. (B) Venn diagram showing the number of genes that are differentially expressed in ZQ, XC, and TO, including shared and independent genes.
FIGURE 7
FIGURE 7
Main functional categories for differentially expressed genes according to MapMan functional plant categories.
FIGURE 8
FIGURE 8
Gene expression of FRO and IRT in ZQ, XC and TO under iron deficiency for 0, 24, 48, 72, and 96 h. (A,D) The expression of FRO and IRT genes in ZQ. (B,E) The expression of FRO and IRT genes in XC. (C,F) The expression of FRO and IRT genes in TO.
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