Rice endosperm accumulates both major types of storage proteins, prolamins and glutelins. Prolamins synthesized in the endoplasmic reticulum (ER) retained within the ER lumen and accumulated in the protein body I (PB I) (Tanaka et al. 1980). However, it remains to be seen what kind of genes regulate the synthesis and accumulation process of rice prolamin polypeptides. Rice prolamins consist of more than 20 polypeptides. These prolamin polypeptides are divided into two classes: cystein-poor (CysP) and cystein-rich (CysR) prolamins. Probably, there are at least two regulation mechanisms for the synthesis and accumulation process of rice prolamins (Matsusaka et al. 2000). Prolamin mutants esp1, esp3 and Esp4, were reported previously by Kumamaru et al. (1987). esp1 mutant decreased several CysP prolamin polypeptides simultaneously, though it did not decrease the remaining CysP and CysR prolamin polypeptides. This suggests that esp1 mutation is not involved in a structural gene encoding prolamin polypeptide, but a gene for the synthesis and accumulation process of some CysP prolamin polypeptides. The isolation and characterization of Esp1 gene may lead to an understanding of the genetic regulation mechanism of synthesis and accumulation of prolamin polypeptides. In this study, as a first step for the isolation of Esp1 gene, we determined the position of Esp1 gene on chromosome 7.

To isolate Esp1 gene, esp1 mutant induced from a japonica rice cv. Kinmaze was crossed with an indica rice cv. Kasalath. F₁ plants were grown and self-pollinated to obtain F₂ seeds. F₂ seeds were cut into half and then the half with embryos were sown. The plants were cultivated to isolate the genomic DNAs from leaves. The remaining half without embryos were used for selecting the homozygous genotype for esp1, based on the storage protein profile by SDSPAGE analysis. Result of linkage analysis using 109 esp1 homozygous F₂ plants showed that the Esp1 locus was mapped within 1.4 cM region, between a PCR marker e81.9-8.2 and an RFLP marker R2677 on chromosome 7 (Fig. 1). To decide the more precise position of Esp1 gene, 910 esp1 homozygous plants selected from other F₂ population, by SDS-PAGE, were used for linkage analysis with two PCR markers, e81.9-8.2 and e83.3-13. Thirty five and twenty seven recombinant plants were observed for e81.9-8.2 and e83.3-13, respectively (Fig. 1). We produced several PCR markers within 1.4 cM region, between 81.9 cM and 83.3 cM from the short arm terminal of chromosome 7. The recombinant plants will be useful for the

construction of high-resolution linkage map, to isolate of Esp1 gene.

References

Kumamaru, T., H. Satoh, N. Iwata, T. Omura and M. Ogawa, 1987. Mutants for rice storage proteins III. Genetic analysis of mutants for storage proteins of protein bodies in the starchy endosperm. Jpn. J. Genet. 62: 333-339.

Matsusaka, H., T. Kumamaru, M. Ogawa and H. Satoh, 2000. Biosynthesis of rice S-poor and S-rich prolamins are regulated by independent genetic system. In Abstract, 4th Inter. Rice Genet. Sym., IRRI. p. 128.

Tanaka, K., T. Sugimoto, M. Ogawa and Z. Kasai, 1980. Isolation and characterization of two types of protein bodies in the rice endosperm. Agric. Biol. Chem. 44: 1633-1639.