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The maize low‐phytic acid 3 encodes a myo ‐inositol kinase that plays a role in phytic acid biosynthesis in developing seeds
Author(s) -
Shi Jinrui,
Wang Hongyu,
Hazebroek Jan,
Ertl David S.,
Harp Teresa
Publication year - 2005
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2005.02412.x
Subject(s) - phytic acid , inositol , mutant , biochemistry , phosphorylation , biosynthesis , inositol phosphate , kinase , biology , inositol trisphosphate , chemistry , gene , receptor
Summary Phytic acid, myo ‐inositol‐1,2,3,4,5,6‐hexa kis phosphate or Ins P 6 , is the most abundant myo ‐inositol phosphate in plant cells, but its biosynthesis is poorly understood. Also uncertain is the role of myo ‐inositol as a precursor of phytic acid biosynthesis. We identified a low‐phytic acid mutant, lpa3 , in maize. The Mu‐insertion mutant has a phenotype of reduced phytic acid, increased myo ‐inositol and lacks significant amounts of myo ‐inositol phosphate intermediates in seeds. The gene responsible for the mutation encodes a myo ‐inositol kinase (MIK). Maize MIK protein contains conserved amino acid residues found in pfkB carbohydrate kinases. The maize lpa3 gene is expressed in developing embryos, where phytic acid is actively synthesized and accumulates to a large amount. Characterization of the lpa3 mutant provides direct evidence for the role of myo ‐inositol and MIK in phytic acid biosynthesis in developing seeds. Recombinant maize MIK phosphorylates myo ‐inositol to produce multiple myo ‐inositol monophosphates, Ins(1/3)P, Ins(4/6)P and possibly Ins(5)P. The characteristics of the lpa3 mutant and MIK suggest that MIK is not a salvage enzyme for myo ‐inositol recycling and that there are multiple phosphorylation routes to phytic acid in developing seeds. Analysis of the lpa2 / lpa3 double mutant implies interactions between the phosphorylation routes.