| Sorbitol is the major and specific product of photosynthesis and transport, as well as the storage carbohydrate for woody Rosaceae plants. Studying the structure and function of sorbitol transporter, which is a key enzyme in sorbitol transport, has an important role in clarifying the mechanism of sorbitol metabolism and its transport in plant. However, relating to sucrose transporter, the research of sorbitol transporter protein is quite limited. In this study, we cloned the complete cDNA sequences of three genes (ST2, ST3, ST4) and the segments of two genes (ST1, ST5) from the leaves of "Gala" using RT-PCR, and we also analysed the various expression pattern of different members of the sorbitol transporter family in different tissues and development stages, which layed a solid foundation for future research on sorbitol mechanism.The results are as followed:1 STs were cloned from fresh leaves of Royal Gala apple(Malus pumila Mill cv. Royal Gala). We were analyzed and found that the ST2 cDNA, which the full length is 1767bp, contains a complete open reading frame (ORF) 1617bp, and encodes a protein of 538 amino acid which is 81% homologous to MdSOT5; the full length of ST3 cDNA is 1841bp and contains a complete ORF 1578bp, encodes a protein of 526 amino acid which is 99% homologous to MdSOT3; the full length of ST4 cDNA is 1868bp and contains a complete ORF 1473bp, encodes a protein of 491amino acid which is also 99% homologous to MdSOT4; ST1 and ST5 are 79% and 96% homologous to Sorbitol transporter genes SOT2 and SOT6, respectively.2 By taking the advantage of Real-Time fluorescence quantitative PCR, we analysed the expression pattern of STs (ST1-ST7) in different tissues and development stages and found that STI,ST2,ST3,ST6,ST7 in the phloem had high relative expression, and hence, they might be responsible for long-distance transport; ST4 might serve as a signal molecule; ST5 was only responsible for phloem loading, and functioned as the short-distance transport protein.
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