A sepal-expressed ADP-glucose pyrophosphorylase gene (NtAGP) is required for petal expansion growth in 'Xanthi' tobacco.
In this study, a tobacco (Nicotiana tabacum 'Xanthi') ADP-glucose pyrophosphorylase cDNA (NtAGP) was isolated from a flower bud cDNA library and the role of NtAGP in the growth of the floral organ was characterized. The expression of NtAGP was high in the sepal, moderate in the carpel and stamen, and low in the petal tissues. NtAGP-antisense plants produced flowers with abnormal petal limbs due to the early termination of the expansion growth of the petal limbs between the corolla lobes. Microscopic observation of the limb region revealed that cell expansion was limited in NtAGP-antisense plants but that cell numbers remained unchanged. mRNA levels of NtAGP, ADP-glucose pyrophosphorylase activity, and starch content in the sepal tissues of NtAGP-antisense plants were reduced, resulting in significantly lower levels of sugars (sucrose, glucose, and fructose) in the petal limbs. The feeding of these sugars to flower buds of the NtAGP-antisense plants restored the expansion growth in the limb area between the corolla lobes. Expansion growth of the petal limb between the corolla lobes was severely arrested in 'Xanthi' flowers from which sepals were removed, indicating that sepal carbohydrates are essential for petal limb expansion growth. These results demonstrate that NtAGP plays a crucial role in the morphogenesis of petal limbs in 'Xanthi' through the synthesis of starch, which is the main carbohydrate source for expansion growth of petal limbs, in sepal tissues.
Kwak
Man Sup
MS
School of Life Sciences and Biotechnology, Korea University, Seoul 136-701, Korea.
Min
Sung Ran
SR
Lee
Si-Myung
SM
Kim
Kyung-Nam
KN
Liu
Jang Ryol
JR
Paek
Kyung-Hee
KH
Shin
Jeong Sheop
JS
Bae
Jung Myung
JM
D015139:Blotting, Southern; D050260:Carbohydrate Metabolism / Q000502:physiology; D049108:Cell Enlargement; D003001:Cloning, Molecular; D016373:DNA, Antisense; D018076:DNA, Complementary; D015536:Down-Regulation; D035264:Flowers / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D015870:Gene Expression; D018745:Genome, Plant; D051599:Glucose-1-Phosphate Adenylyltransferase / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D019441:Plant Epidermis / Q000254:growth & development; D011401:Promoter Regions, Genetic; D014026:Nicotiana / Q000166:cytology / Q000254:growth & development* / Q000502:physiology
D016373:DNA, Antisense; D018076:DNA, Complementary; D051599:Glucose-1-Phosphate Adenylyltransferase