Abstract
BackgroundLimited information is available on aluminum (Al)-toxicity-responsive proteins in woody plant roots. Seedlings of ‘Xuegan’ (Citrus sinensis) and ‘Sour pummelo’ (Citrus grandis) were treated for 18 weeks with nutrient solution containing 0 (control) or 1.2 mM AlCl3 · 6H2O (+Al). Thereafter, we investigated Citrus root protein profiles using isobaric tags for relative and absolute quantification (iTRAQ). The aims of this work were to determine the molecular mechanisms of plants to deal with Al-toxicity and to identify differentially expressed proteins involved in Al-tolerance.ResultsC. sinensis was more tolerant to Al-toxicity than C. grandis. We isolated 347 differentially expressed proteins from + Al Citrus roots. Among these proteins, 202 (96) proteins only presented in C. sinensis (C. grandis), and 49 proteins were shared by the two species. Of the 49 overlapping proteins, 45 proteins were regulated in the same direction upon Al exposure in the both species. These proteins were classified into following categories: sulfur metabolism, stress and defense response, carbohydrate and energy metabolism, nucleic acid metabolism, protein metabolism, cell transport, biological regulation and signal transduction, cell wall and cytoskeleton metabolism, and jasmonic acid (JA) biosynthesis. The higher Al-tolerance of C. sinensis may be related to several factors, including: (a) activation of sulfur metabolism; (b) greatly improving the total ability of antioxidation and detoxification; (c) up-regulation of carbohydrate and energy metabolism; (d) enhancing cell transport; (e) decreased (increased) abundances of proteins involved in protein synthesis (proteiolysis); (f) keeping a better balance between protein phosphorylation and dephosphorylation; and (g) increasing JA biosynthesis.ConclusionsOur results demonstrated that metabolic flexibility was more remarkable in C. sinenis than in C. grandis roots, thus improving the Al-tolerance of C. sinensis. This provided the most integrated view of the adaptive responses occurring in Al-toxicity roots.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2133-9) contains supplementary material, which is available to authorized users.
Highlights
Limited information is available on aluminum (Al)-toxicity-responsive proteins in woody plant roots
It is worth mentioning that 1.2 mM Al treatment decreased C. grandis root Dry weight (DW), but had no influence on C. sinensis root DW and that Al-toxicity-induced decreases in whole plant and shoot DWs were more severe in C. grandis than in C. sinensis seedlings, when 20 μM H3BO3 in nutrient solution was replaced by 2.5 μM H3BO3
Al-induced inhibition of nucleic acid biosynthesis We found that all these differentially expressed proteins related to nucleic acid metabolism in C. sinensis and C. grandis roots except for protein RAD-like 3 involved in regulation of transcription in the two species and ribonuclease, which catalyzes the degradation of RNA into smaller components in C. grandis, were down-regulated in response to Al-toxicity (Additional file 2), demonstrating that Al-toxicity might impair nucleic acid biosynthesis in C. sinensis and C. grandis roots and increased RNA degradation in C. grandis roots
Summary
Limited information is available on aluminum (Al)-toxicity-responsive proteins in woody plant roots. The aims of this work were to determine the molecular mechanisms of plants to deal with Al-toxicity and to identify differentially expressed proteins involved in Al-tolerance. In many acidic soils through the tropics and subtropics, aluminum (Al)-toxicity is a major factor limiting crop productivity. A more efficient strategy is to breed Al-tolerant crop cultivars. The success of breeding programs relies on an understanding of the physiological, biochemical and molecular mechanisms that plants tolerate Al-toxicity. Since biological processes are controlled by proteins, identification and characterization of Al-tolerant proteins will increase our understanding of the molecular mechanisms on plant Al-tolerance, and will provide new information that researchers will use to screen and breed crop cultivars suited for acidic soils with higher active Al
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