Poster: Seed biology

Abs # 728: The pyruvate orthophosphate dikinase gene (OSPPDKB) affects starch biosynthesis during grain filling and developing in rice

Presenter:	Kang, Hong-Gyu , honggyu@postech.ac.kr
Authors	Kang, Hong-Gyu  (A)   Park, Sunhee  (A)   Matsuoka, Makoto  (B)   An, Gynheung  (A)
Affiliations:	(A): Pohang University of Science and Technology (B): Nagoya University

Offspring from a transgenic rice plant generated by the Agrobacterium-dependent T-DNA tagging procedure were found to segregate for an opaque white endosperm phenotype. The opaque phenotype of the transgenic plant was inherited as a recessive mutation that co-segregated with the T-DNA insert. The DNA sequence flanking the T-DNA indicated that T-DNA is inserted into the 5th intron of the OsPPDKB gene encoding pyruvate orthophosphate dikinase (PPDK). RNA and Western gel blot analyses showed that the homozygous mutant line (osppdkb-1/osppdkb-1) did not produce the OSPPDKB transcript and the OSPPDKB protein, respectively. To confirm that the opaque phenotype was generated by disruption of the OsPPDKB gene, we have isolated additional two alleles, osppdkb-2 and osppdkb-3 by reverse genetic screening. One was mutated by the T-DNA insertion into the 5th intron of the gene like osppdkb-1 and the other by the Tos17 insertion into the 10th exon of the gene. Both of alleles also showed exactly the same opaque white endosperm phenotype as osppdkb-1. The 1000-kernel weight of the mutant seeds was reduced by about 6% compared to that of the normal seeds. Under SEM, the opaque grain had round and loosely packed compound starch granules like that of milky-white rice kernel. Starch content of the mutant grains was similar to that of the normal grains. Crude protein content was slightly higher in the opaque grains than the normal grains. The fact indicated that the weight reduction in the opaque grains was probably due to the unfavorable accumulation of starch in the stage of ripening. PPDK is known for its role in C4 photosynthesis but has no firmly established function in the developing seeds of C3 and C4 plants. We are elucidating its role during grain filling or seed development.