title: Leaf cDNA-AFLP analysis of two citrus species differing in manganese tolerance in response to long-term manganese-toxicity.
abstract: BACKGROUND
  Very little is known about manganese (Mn)-toxicity-responsive genes in citrus plants. Seedlings of 'Xuegan' (Citrus sinensis) and 'Sour pummelo' (Citrus grandis) were irrigated for 17 weeks with nutrient solution containing 2 μM (control) or 600 μM (Mn-toxicity) MnSO₄. The objectives of this study were to understand the mechanisms of citrus Mn-tolerance and to identify differentially expressed genes, which might be involved in Mn-tolerance.
  
  
  RESULTS
  Under Mn-toxicity, the majority of Mn in seedlings was retained in the roots; C. sinensis seedlings accumulated more Mn in roots and less Mn in shoots (leaves) than C. grandis ones and Mn concentration was lower in Mn-toxicity C. sinensis leaves compared to Mn-toxicity C. grandis ones. Mn-toxicity affected C. grandis seedling growth, leaf CO₂ assimilation, total soluble concentration, phosphorus (P) and magenisum (Mg) more than C. sinensis. Using cDNA-AFLP, we isolated 42 up-regulated and 80 down-regulated genes in Mn-toxicity C. grandis leaves. They were grouped into the following functional categories: biological regulation and signal transduction, carbohydrate and energy metabolism, nucleic acid metabolism, protein metabolism, lipid metabolism, cell wall metabolism, stress responses and cell transport. However, only 7 up-regulated and 8 down-regulated genes were identified in Mn-toxicity C. sinensis ones. The responses of C. grandis leaves to Mn-toxicity might include following several aspects: (1) accelerating leaf senescence; (2) activating the metabolic pathway related to ATPase synthesis and reducing power production; (3) decreasing cell transport; (4) inhibiting protein and nucleic acid metabolisms; (5) impairing the formation of cell wall; and (6) triggering multiple signal transduction pathways. We also identified many new Mn-toxicity-responsive genes involved in biological and signal transduction, carbohydrate and protein metabolisms, stress responses and cell transport.
  
  
  CONCLUSIONS
  Our results demonstrated that C. sinensis was more tolerant to Mn-toxicity than C. grandis, and that Mn-toxicity affected gene expression far less in C. sinensis leaves. This might be associated with more Mn accumulation in roots and less Mn accumulation in leaves of Mn-toxicity C. sinensis seedlings than those of C. grandis seedlings. Our findings increase our understanding of the molecular mechanisms involved in the responses of plants to Mn-toxicity.
authors.affiliation: Institute of Horticultural Plant Physiology, Biochemistry and Molecular Biology, Fujian Agriculture and Forestry University, 350002 Fuzhou, China. lisongchen2002@hotmail.com.
authors.forename: Chen-Ping
authors.initials: CP
authors.lastname: Zhou
authors.forename: Yi-Ping
authors.initials: YP
authors.lastname: Qi
authors.forename: Xiang
authors.initials: X
authors.lastname: You
authors.forename: Lin-Tong
authors.initials: LT
authors.lastname: Yang
authors.forename: Peng
authors.initials: P
authors.lastname: Guo
authors.forename: Xin
authors.initials: X
authors.lastname: Ye
authors.forename: Xin-Xing
authors.initials: XX
authors.lastname: Zhou
authors.forename: Feng-Jiao
authors.initials: FJ
authors.lastname: Ke
authors.forename: Li-Song
authors.initials: LS
authors.lastname: Chen
mesh_terms: D054458:Amplified Fragment Length Polymorphism Analysis; D002957:Citrus / Q000235:genetics* / Q000502:physiology; D018076:DNA, Complementary / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008345:Manganese / Q000633:toxicity*; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology*; D018517:Plant Roots / Q000502:physiology; D036226:Seedlings / Q000502:physiology
chemical_list: D018076:DNA, Complementary; D008345:Manganese
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