Abstract：Sucrose which involved in the plant growth and development processes, the signal transduction pathway and other physiological activities is an important carbon source in plants. Sucrose transporter genes (SUT) play a key role in the long distance transport activities of sucrose in plants. In order to understand the transport mechanism of the SUT in Paeonia suffruticosa, P. suffruticosa 'Luoyanghong' was used as experimental materials in this study. The sucrose transporter gene named PsSUT2 was separated and cloned from the leaf by reverse transcription-PCR (RT-PCR) and rapid-amplification of cDNA ends (RACE). The full length cDNA of PsSUT2 is 2 347 bp, and the ORF encoding a protein of 601 amino acids, was 1 803 bp. The accession number is KC542396 in GenBank. Its molecular mass was 64.6 kD and pI was 6.14, The homologous amino acid sequence of PsSUT2 compared with that of SUT gene from Vitis vinifera was 75.27%. PsSUT2 protein contained 12 transmembrane helical structures, which belongs to the major facilitator superfamily (MFS). The relative expression of PsSUT2 gene and the soluble content in different organs were determined with qRT-PCR and chromatography technology at the different developmental stage of tree peony. The main results showed that the PsSUT2 gene expressed abundantly in the petals at the flowering stage, and the relative expression was 11.18, which was significantly different from other organs of the same stage even every organ of other stages. Meanwhile, the PsSUT2 gene expressed in every organ such as the root, the perennial stem, the leaf, the bulbil, the petal at different developmental stage, but the relative expression were low, for example, the relative expression of petals in the flowering stage was 4.26 times as much as that of roots in the same stage, and 4.40 times as much as that of roots in the little bell stage, and 10.48 times as much as that of petals in the peach stage, and 30.55 times as much as that of bulbil in the bulbil differentiation stage. So, it indicated that the PsSUT2 gene took part in the sucrose unloading activities in the sink organs probably. The contents of sucrose, glucose and fructose of every organ were significantly different at different developmental stage of tree peony, and there was no sucrose almost but much more glucose and fructose in the bulbil or petal before the arrival of flowering. So, the petal of P. suffruticosa 'Luoyanghong' accumulated hexose (glucose and fructose) mainly and the accumulation of hexose was benifit to the flower opening. However, the differences were significantly negative between the sucrose content of leaf, the glucose content of root and the relative expression level of PsSUT2 by the correlative analysis method. Therefore, The expression of the PsSUT2 gene may be inhibited by the sucrose in the leaves and the glucose accumulation in the roots. The results provide a theoretical basis for further understanding of the function of the PsSUT2 gene, and the next step, the gene can be used to carry out molecular breeding and genetic improvement work on the tree peony.
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