Identification of manganese-toxicity-responsive genes in roots of two citrus species differing in manganese tolerance using cDNA-AFLP

Abstract

We identified more Mn-toxicity-responsive genes from Mn-intolerant Citrus grandis than from Mn-tolerant Citrus sinensis roots. These findings increased our understanding of the molecular mechanisms on plant Mn toxicity and Mn tolerance. Manganese (Mn) toxicity is the most important factor limiting crop production after aluminum toxicity in acidic soils. However, little is known about Mn-toxicity-induced alterations of gene expression profiles in woody plants. Using cDNA-AFLP, we identified 87 and 63 Mn-toxicity-responsive genes from Mn-intolerant ‘Sour pummelo’ (Citrus grandis) and Mn-tolerant ‘Xuegan’ (Citrus sinensis) roots. Among these genes, only 22 genes with the same accession number were shared by both. Protein phosphorylation/dephosphorylation-related genes were upregulated in C. sinensis roots, and downregulated in C. grandis roots except for one differentially expressed gene. Sulfur metabolism-related genes were repressed only in Mn-toxic C. grandis roots. Obviously, great differences existed in Mn-toxicity-induced alterations of gene expression profiles between C. sinensis and C. grandis roots. Genes related to protein phosphorylation/dephosphorylation (i.e., cyclin-dependent kinase-activating kinase assembly factor-related protein and PP2A regulatory subunit TAP46), cellular transport (i.e., Ca-transporting ATPase 1), and nucleic acid (i.e., ethylene-responsive transcription factor ERF109-like, structural maintenance of chromosomes protein 4-like, RNA-binding protein and DEAD-box ATP-dependent RNA helicase 21), cell wall (i.e., pectin methylesterase 1 and invertase/pectin methylesterase inhibitor family protein) and fatty acid (i.e., carboxylesterase 20) metabolisms might play a role in C. sinensis Mn tolerance. In addition, cell wall materials were increased in Mn-toxic C. sinensis and C. grandis roots, especially in the former. Interestingly, lignin content was increased in Mn-toxic C. sinensis roots, while a reverse trend was displayed in Mn-toxic C. grandis roots. In conclusion, our results provided novel clues to the molecular mechanisms on Mn toxicity and Mn tolerance in higher plants.