|Budget Amount *help
¥14,400,000 (Direct Cost : ¥14,400,000)
Fiscal Year 1999 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1998 : ¥1,200,000 (Direct Cost : ¥1,200,000)
Fiscal Year 1997 : ¥12,400,000 (Direct Cost : ¥12,400,000)
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.