Abstract
The major translocating sugar of Rosaceae is sorbitol, a kind of polyol. Polyol transporters of plants are classified into two groups; Group I transporters have been well studied and shown to localize in plasma membrane. Although little information about Group II has been reported, myo-inositol transporters of Mesembryanthemum crystallinum (McITR) was firstly identified as a vacuolar membrane polyol transporter in plants. Thus this homolog of Rosaceae may involve in sugar accumulation of fruit vacuole. We isolated two cDNAs, PcITR1 and PcITR2 from pear belonging to Group II. PcITR1 transcripts are high in all organs except in leaves, whereas PcITR2 transcripts are high in leaves. Sugar transport activities of PcITR1 could not be detected in heterologous expression system of yeast. The GFP-PcITR1 fusion protein localized to the plasma membrane in Arabidopsis cell meaning Group II includes not only plasma membrane polyol transporters but also vacuolar ones.
