Glutelin is the major storage protein in the rice endosperm. In SDS-PAGE analysis, glutelin acidic and basic subunits are separated into respective three major bands. They are named as Alpha-1, Alpha-2 and Alpha-3 for acidic subunit and Beta-1, Beta-2 and Beta-3 for basic subunit. On the other hand in IEF analysis, the acidic and basic subunits are further separated into ten and nine bands, respectively electrophoresis (Uemura et al., 1996). It was made it clear that each of the IEF bands consists of a discrete polypeptide by 2-dementional. The nucleotide sequences for glutelin polypeptides showed that there are at least ten genes encoding glutelin polypeptides in rice genome, which are grouped into two subfamilies named as GluA and GluB (Takaiwa et al. 1987). We have identified 5 glutelin genes on the basis of discrete glutelin polypeptide band pattern by IEF such as Glu1, Glu2, Glu3, Glu4 and Glu5 which locate on chromosome 1 or 2 (Uemura et al. 1996). Iida et al. (1997) also found the glutelin gene which was located on the chromosome 10 and was designated as glu2. In this study, we report here a novel glutelin gene located on chromosome 3.

We found a wide variation of glutelin subunit polypeptides by 2D among varieties preserved in Kyushu University (Uemura et al. 1996). In comparison of IEF band pattern of glutelin, Nipponbare (a japonica cv.) had pI 6.55 band without pI 6.52 band, whereas Kasalath (an indica cv.) possessed pI 6.52 band but lack in pI 6.55 band in IEF analysis (Fig. 1). These IEF bands correspond to Alpha-2 band (38kD) of acidic subunit in SDS-PAGE (data not shown).

To investigate the genetic behavior of pI 6.55 and pI 6.52 bands, F₃ seeds from the cross between Nipponbare and Kasalath were analyzed. Segregation mode in F₃ population showed that these two bands were controlled by respective incomplete single dominant genes. No recombinants which had both pI 6.55 and pI 6.52 bands or lost both of them were observed,

suggesting that the genes controlling these bands are allelic. The gene controlling pI 6.55 or pI 6.52 band was independent from genes reported previously that control the other glutelin polypeptides located on chromosome 1 and 2. The linkage analysis by RFLP showed that the gene controlling pI 6.55 or pI 6.52 band mapped between C1677 and L708 on chromosome 3 (Fig. 2). The locus controlling pI 6.55 and pI 6.52 glutelin band was designated Glu6.

This study was partly supported by Bio-oriented Technology Research Advancement Institution (BRAIN), Japan.

References

Iida S., M. Kusaba and T. Nishio 1997. Mutants lacking glutelin subunits in rice: mapping and combination of mutated glutelin genes. Theor. Appl. Genet. 94: 177-183.

Takaiwa F, Kikuchi S, Oono K. 1987. A rice glutelin gene family-A major type of glutelin mRNAs can be divided into two classes. Mol. Gen. Genet. 205: 15-22.

Uemura Y., H. Satoh, M. Ogawa, H. Suehisa, T.C. Katayama and A. Yoshimura, 1996. In Rice Genetics III. pp.471- 476. IRRI, Manila, Philippines.

Yamagata H, Tanaka K, Kasai Z. 1982. Evidence for a precursor form of rice glutelin subunits. Agric. Biol. Chem. 46(1): 321-322.