ROLES FOR SUCROSE TRANSPORTERS DURING TUBEROUS ROOT DEVELOPMENT IN SWEET POTATO

为了研究蔗糖转运蛋白在甘薯中的作用，我克隆了三个与植物蔗糖转运蛋白同源的cdna （IbSUT1， IbSUT2和IbSUT3）。与马铃薯、拟南芥和蚕豆的蔗糖转运蛋白在核苷酸水平上的同源性为60 ~ 72%，在氨基酸水平上的同源性为58 ~ 77%。基因组Southern blot分析结果表明，蔗糖转运蛋白基因在甘薯中构成一个小基因家族。IbSUT1、IbSUT2和IbSUT3转录本的大小分别约为3.1kb、2.4kb和1.6kb。IbSUT1、IbSUT2和IbSUT3的表达模式有明显差异。IbSUT1在所有器官中的表达量大致相等。叶柄和幼根中IbSUT2的RNA水平比叶片、匍匐茎和块根中IbSUT2的RNA水平高出至少2倍。IbSUT3在叶柄中转录水平最高，在其他器官中转录水平低约30%。在块根发育过程中，在根中发现IbSUT1的mRNA水平大致相等，而IbSUT2和IbSUT3的mRNA水平持续下降。这些结果表明，甘薯至少有三种蔗糖转运体，而IbSUT1是块根发育所必需的。

To study roles of sucrose transporters in sweet potato, I cloned three cDNAs (IbSUT1, IbSUT2 and IbSUT3) for proteins with homologies to plant sucrose transporters. The cDNAs showed 60 to 72% identity at the nucleotide level and 58 to 77% identity at the amino acid level to sucrose transporters from potato, Arabidopsis and fava bean. Based on the result of genomic Southern blot analysis, the sucrose transporter gene appears to constitute a small gene family in sweet potato. The size of transcripts of IbSUT1, IbSUT2 and IbSUT3 was about 3.1kb, 2.4kb and 1.6kb, respectively. IbSUT1, IbSUT2 and IbSUT3 had markedly different expression patterns. IbSUT1 was expressed in approximately equal amounts in all organs. RNA levels of IbSUT2 in petioles and young roots were at least two times higher than those in leaf blades, stolons and tuberous roots. The highest transcript level for IbSUT3 was found in petioles, and about 30% lower levels at the other organs. Approximately equal levels of mRNA for IbSUT1 were found in roots during tuberous root development, whereas mRNA levels of IbSUT2 and IbSUT3 continued to decrease. These results indicate sweet potato has at least three kinds of sucrose transporters and IbSUT1 is required for tuberous root development.