Leaf adaptive responses to aluminum-toxicity revealed by RNA-Seq in two citrus species with contrasting aluminum tolerance

Background: Limited data are available on aluminum (Al)-toxicity-induced alterations of gene profiles in woody plants. Seedlings of Al-tolerant Citrus sinensis and Al-intolerant Citrus grandis were fertigated with nutrient solution containing 0 and 1.0 mM AlCl3•6H2O. Thereafter, we investigated the Al-toxicity-induced alterations of transcriptomics in leaves by RNA-Seq. Results: Using RNA-seq, we isolated 1162 (181) up- and 496 (234) downregulated genes from Al-treated C. grandis (C. sinensis) leaves. Clearly, gene expression was less affected by Al-toxicity in C. sinensis leaves than in C. grandis ones. Several Al-toxicity-responsive genes homologous to known Al-tolerance genes: ALUMINUM SENSITIVE 3 (ALS3), multidrug and toxic compound extrusion (MATE), glutathione S-transferase (GST), L-galactose dehydrogenase(L-GalDH) and lipoxygenase (LOX) were identified in citrus leaves. Genes related to signal transduction, and sulfur transport and metabolism might also play a role in the higher Al-tolerance of C. sinensis. Conclusions: This is the first comparative investigation of transcriptomic responses in Al-treated citrus leaves. There were common and unique mechanisms for citrus Al-tolerance. These results provide a platform for further investigating the roles of genes possibly responsible for citrus Al-tolerance. Overall design: Examination of mRNA levels in control and Al-treatment leave of C. grandis and C. sinensis with two biological replicates were generated by deep sequencing, using Illumina HiSeq 2000 device.