Loss of cytosolic fructose-1,6-bisphosphatase limits photosynthetic sucrose synthesis and causes severe growth retardations in rice (Oryza sativa).
During photosynthesis, triose-phosphates (trioseP) exported from the chloroplast to the cytosol are converted to sucrose via cytosolic fructose-1,6-bisphosphatase (cFBPase). Expression analysis in rice suggests that OscFBP1 plays a major role in the cytosolic conversion of trioseP to sucrose in leaves during the day. The isolated OscFBP1 mutants exhibited markedly decreased photosynthetic rates and severe growth retardation with reduced chlorophyll content, which results in plant death. Analysis of primary carbon metabolites revealed both significantly reduced levels of sucrose, glucose, fructose and starch in leaves of these mutants, and a high accumulation of sucrose to starch in leaves of rice plants. In the oscfbp1 mutants, products of glycolysis and the TCA cycle were significantly increased. A partitioning experiment of (14)C-labelled photoassimilates revealed altered carbon distributions including a slight increase in the insoluble fraction representing transitory starch, a significant decrease in the neutral fraction corresponding to soluble sugars and a high accumulation of phosphorylated intermediates and carboxylic acid fractions in the oscfbp1 mutants. These results indicate that the impaired synthesis of sucrose in rice cannot be sufficiently compensated for by the transitory starch-mediated pathways that have been found to facilitate plant growth in the equivalent Arabidopsis mutants.
Lee
Sang-Kyu
SK
Plant Metabolism Research Center & Graduate School of Biotechnology, Kyung Hee University, Yongin 446-701, Korea.
Jeon
Jong-Seong
JS
Börnke
Frederik
F
Voll
Lars
L
Cho
Jung-Il
JI
Goh
Chang-Hyo
CH
Jeong
Suk-Won
SW
Park
Youn-Il
YI
Kim
Sung Jin
SJ
Choi
Sang-Bong
SB
Miyao
Akio
A
Hirochika
Hirohiko
H
An
Gynheung
G
Cho
Man-Ho
MH
Bhoo
Seong Hee
SH
Sonnewald
Uwe
U
Hahn
Tae-Ryong
TR
D002250:Carbon Radioisotopes / Q000378:metabolism; D002734:Chlorophyll / Q000032:analysis; D003600:Cytosol / Q000378:metabolism; D006597:Fructose-Bisphosphatase / Q000235:genetics / Q000378:metabolism*; D017343:Genes, Plant; D016254:Mutagenesis, Insertional; D009154:Mutation; D012275:Oryza / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D010710:Phosphates / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D018749:RNA, Plant / Q000235:genetics; D013213:Starch / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism*
D002250:Carbon Radioisotopes; D010710:Phosphates; D010940:Plant Proteins; D018749:RNA, Plant; D002734:Chlorophyll; D013395:Sucrose; D013213:Starch; D006597:Fructose-Bisphosphatase