Two sweetpotato ADP-glucose pyrophosphorylase isoforms are regulated antagonistically in response to sucrose content in storage roots.
The transcriptional regulation of ADP-glucose pyrophosphorylase (AGPase) genes in detached leaves in response to exogenous sucrose has been investigated earlier; however the effects of endogenous sucrose on AGPase gene transcription in leaves or starch-accumulating tissues have not yet been determined. We therefore have investigated the relationship between endogenous sucrose content in the storage tissues of sweetpotato (Ipomoea batatas cv. Yulmi) and the rate of transcription of the two sweetpotato AGPase isoforms, ibAGP1 and ibAGP2, by means of transient expression analysis of their promoters. Sequence analysis of the two promoters identified putative sucrose-responsive elements on the ibAGP1 promoter and, conversely, putative sucrose-starvation elements on the ibAGP2 promoter. Transient expression analyses on transverse storage root sections revealed that the ibAGP1 and ibAGP2 promoters directed strong expression in the sweetpotato storage roots (diameter: 1.5 cm). Sucrose contents of the sweetpotato storage roots were positively correlated with growth of the storage root. In the storage roots, ibAGP1 promoter activity became stronger with increasing endogenous sucrose levels, while ibAGP2 promoter activity became markedly weaker. Consequently, ibAGP2 was expressed primarily during the early stages of storage root development, whereas ibAGP1 was abundantly expressed in the later stages, during which a profound level of starch accumulation occurs. The antagonistic regulation of the two promoters in response to endogenous sucrose levels was also confirmed in carrot (Daucus carota L. cv. Hapa-ochon) taproots.
Kwak
Man Sup
MS
School of Life Sciences and Biotechnology, Korea University, Seoul, 136-701, South Korea.
Noh
Seol Ah
SA
Oh
Mi-Joung
MJ
Huh
Gyung Hye
GH
Kim
Kyung-Nam
KN
Lee
Shin Woo
SW
Shin
Jeong Sheop
JS
Bae
Jung Myung
JM
D001483:Base Sequence; D018552:Daucus carota / Q000235:genetics / Q000254:growth & development; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D051599:Glucose-1-Phosphate Adenylyltransferase / Q000096:biosynthesis* / Q000235:genetics; D027723:Ipomoea batatas / Q000235:genetics / Q000254:growth & development*; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000096:biosynthesis* / Q000235:genetics; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development*; D011401:Promoter Regions, Genetic / Q000502:physiology; D013213:Starch / Q000096:biosynthesis; D013395:Sucrose / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology
D007527:Isoenzymes; D010940:Plant Proteins; D013395:Sucrose; D013213:Starch; D051599:Glucose-1-Phosphate Adenylyltransferase