Poster: Seed Biology

Abs # 540: An inositol phosphate kinase gene involved in phytic acid biosynthesis in developing maize seeds.

Presenter:	Shi, Jinrui , jinrui.shi@pioneer.com
Authors	Shi, Jinrui  (A)   Wang, Hongyu  (A)   Wu, Yunsheng  (A)   Hazebroek, Jan  (A)   Meeley, Robert B. (A)   Ertl, David S. (A)
Affiliations:	(A): Pioneer Hi-Bred International

It has been proposed that phytic acid in plant seeds is synthesized from Ins(3)P through a series of phosphorylations catalyzed by inositol phosphate kinase(s). A few inositol phosphate kinases have been purified from plants, but their role in phytic acid biosynthesis is unknown. We identified a maize inositol phosphate kinase (ZmIpk) gene through sequence comparison with human and Arabidopsis Ins(1,3,4)P3 5/6-kinase genes. The recombinant maize ZmIpk protein, expressed and purified from E. coli, has kinase activity on several inositol polyphosphates, including Ins(1,3,4)P3, Ins(3,5,6)P3, Ins(3,4,5,6)P4 and Ins(1,2,5,6)P4. The maize ZmIpk mRNA is expressed in the embryo, the organ where phytic acid accumulates in maize seeds. The ZmIpk Mutator-insertion mutants were identified from a Mutator F2 family. In the ZmIpk Mu-insertion mutants, seed phytic acid content is reduced approximately 30% and inorganic phosphate is increased about three-fold. The mutants also accumulate myo-inositol and inositol phosphates as in the low-phytic acid mutant lpa2. Allelic tests showed that the ZmIpk Mu-insertion mutants are allelic to the lpa2. Southern blotting analysis, cloning and sequencing of the ZmIpk gene from lpa2 revealed that the lpa2-1 allele is caused by the genomic sequence rearrangement in the ZmIpk locus and the lpa2-2 allele has a nucleotide mutation that generated a stop codon in the N-terminal region of the ZmIpk open reading frame. These results provide evidence that ZmIpk is one of the kinases responsible for phytic acid biosynthesis in developing maize seeds.