Rice SPK, a calmodulin-like domain protein kinase, is required for storage product accumulation during seed development: phosphorylation of sucrose synthase is a possible factor.
Suc, an end product of photosynthesis, is metabolized by Suc synthase in sink organs as an initial step in the biosynthesis of storage products. Suc synthase activity is known to be regulated by reversible phosphorylation, but the details of this process are unclear at present. Rice SPK, a calcium-dependent protein kinase, is expressed uniquely in the endosperm of immature seed, and its involvement in the biosynthetic pathways of storage products was suggested. Antisense SPK transformants lacked the ability to accumulate storage products such as starch, but produced watery seed with a large amount of Suc instead, as the result of an inhibition of Suc degradation. Analysis of in vitro phosphorylation indicated that SPK phosphorylated specifically a Ser residue in Suc synthase that has been shown to be important for its activity in the degradation of Suc. This finding suggests that SPK is involved in the activation of Suc synthase. It appears that SPK is a Suc synthase kinase that may be important for supplying substrates for the biosynthesis of storage products.
Asano
Takayuki
T
Department of Biological Science and Technology, Science University of Tokyo, 2641 Yamazaki, Noda 278-8510, Japan.
Kunieda
Noriko
N
Omura
Yuhi
Y
Ibe
Hirokazu
H
Kawasaki
Tsutomu
T
Takano
Makoto
M
Sato
Miho
M
Furuhashi
Hideyuki
H
Mujin
Toshiyuki
T
Takaiwa
Fumio
F
Wu Cy
Chuan-yin
CY
Tada
Yuichi
Y
Satozawa
Tomomi
T
Sakamoto
Masahiro
M
Shimada
Hiroaki
H
D000595:Amino Acid Sequence; D005632:Fructose / Q000096:biosynthesis; D015971:Gene Expression Regulation, Enzymologic; D005947:Glucose / Q000096:biosynthesis; D007527:Isoenzymes / Q000378:metabolism; D008969:Molecular Sequence Data; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D010766:Phosphorylation; D010788:Photosynthesis; D010940:Plant Proteins; D030821:Plants, Genetically Modified; D011494:Protein Kinases / Q000235:genetics* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012639:Seeds / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism; D013213:Starch / Q000096:biosynthesis; D013395:Sucrose / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases
D005632:Fructose; D005947:Glucose; D007527:Isoenzymes; D010940:Plant Proteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D012694:Serine; D013213:Starch; D013395:Sucrose; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C102599:sucrose synthase kinase