Root transcriptome analysis on the grape genotypes with contrast translocation pattern of excess manganese from root to shoot

The root-to-shoot transport of manganese (Mn) exhibited intra-specific characters in different grape genotypes. The majority of Mn was stored in the roots of the grape cultivar Jinshou, while it was mainly transferred to the shoots in the cultivar Combier. The aims of the present study was to reveal the complex interplay of gene expression endowing grape a high tolerance to excess Mn and to explore the relation of the expression of Mn transporters with the contrast root-to-shoot translocation pattern of excess Mn in different grape cultivars. The root transcriptome changes in both cultivars were analyzed by high-throughput sequencing and validated by quantitative RT-PCR. Compared to Jinshou, Combier exhibited a markedly high transcripts level in the Mn transporter unigenes in the roots independent of the Mn treatment, accompanied by a higher expression level of genes encoding nicotianamine synthase, heavy metal-transporting ATPase, ZIP family member and IRT1-like proteins, which could facilitate Mn transport from the roots to the shoots in Combier. However, the expression level of genes involved in the subcellular vesicular transport pathway was much higher in Jinshou than in Combier, with a higher transcripts level of V-ATPase, vacuolar protein and the proteins for the synthesis of organic acid, such as the citrate cycle and glycolysis pathway. All of these changes allowed Mn to be easily chelated and compartmented to root cortical and epidermic cell vacuoles in Jinshou, accompanied with higher transcription and activity levels of stress-related enzymes, endowing Jinshou a high degree of tolerance to excess Mn. The grape transcriptome responses to Mn stress were also discussed.