Cloning And Expression Analysis Of Sucrose Transporters In Cassava(Manihot Esculenta Crantz)

Cassava, Euphorbiaceae plant, is the sixth largest food crops in the world. It originated in the American tropical area with typical features, such as high photosynthetic efficiency, powerful starch accumulation in tuber root, weathering an extremely adaptation to drought and barren soil conditions. In China, cassava is an important industrial raw material for starch and biofuel industries. The starch yielding in tuber root involve in the coordination of "Source-Flow-Sink "relationship of cassava plant of which sucrose is the main transport form of the photosynthetic product. It is essential to understand how the sucrose loading in leave and un-loading in the tuber roots for increasing starch productivity, however, it is not clear in cassava up to now. Although sucrose transporter (SUT) is the carrier for active transport of sucrose, the biological function of them has not yet reported in cassava. The study completed cloning of several kinds of SUTs of cassava and classified them by bioinformatics analysis, and investigated their expression pattern in different developmental stages. The general results show as the following:There were four different fragments of SUTs amplified and cloned by RT-PCR with designed a pair of degenerate primers referenced to the conserved region of sucrose transporter genes in Genbank. They were ascribed into three types of SUT and named as MeSUT1x, MeSUTly, MeSUT2å’ŒMeSUT4according to evolutional tree analysis.The full-length cDNA sequence of MeSUT4cloned through RACE has1491bp nucleotide acids which encoding496amino acids with trans-membrane protein characteristics owed y secondary structure twelve domains.Quit different expression pattern of three SUTs in organs and developing stages of cassava have been revealed by Real-time quantitative PCR (qPCR). The expression of all three MeSUTs in leave of Arg7and SC124is much higher than in their tuber roots. Among the different developmental stages, the leave expression of MeSUTs is higher in former and mid stages than in the late stage but in tuber roots the expression is relatively higher in early stage than back stages. For day and night vary, the expression of all three MeSUTs is the highest in12:00noon, but is lower in the6:00early morning and0:00midnight, whatever in leaf or tuber roots. It means that expression of the MeSUTs is regulated by sugar concentration and light cycle with diurnal rhythm. Comparison of MeSUTs expression levels between cultivar and wild species, the expression level in cultivar with high starch productivity is significantly higher than in the wild species whatever in leave or tuber rootsThere were differential expressions among the three MeSUTs. MeSUTl has shown the highest activity in all time of leaf and the early developing stage of tuber roots. The MeSUT2 rank the second. And MeSUT4owned comparatively higher activity in the late development stage of tuber roots It is indicated that MeSUTl will play an important role in phloem loading process in leave, and perhaps being the symplastic transportation in sucrose unloading in tuber roots but MeSUTl, MeSUT4still may play a role. In the article, we discussed how to resolve the cassava sucrose transport mechanisms and their contribution to starch accumulated.