The glutelin precursor (glup) mutant genes have been genetically characterized and found that there are 9 different loci, esp2 and Glup1 to glup8 (Kumamaru et al. 1988, Satoh et al. 1994, 1999, Tian et al. 2001). Recently genetic analysis indicated that glup6 independent of other glup genes and glup6 was epistatic to genes for Glup1, glup2, glup3 and Glup5 , hypostatic to esp2 gene (Tian et al. 2001) and additive by glup4 gene.

The SDS-PAGE profile of total seed storage proteins in endosperm of glup6 mutant, EM939, was similar to that of esp2 mutants, the co-reduction of mature glutelins and cystein-poor 13kD b prolamins and 26kD globulin with the accumulation of high amount of 57kD polypeptides (Tian et al. 2001). Since esp2 mutation was caused by the lesion of gene encoding the endosperm specific protein disulfide isomerase (PDI) which is a key enzyme in the sorting out of proglutelin and prolamin polypeptides within endoplasmic reticulumn (ER) lumen (Takemoto et al. 2002). glup6 mutation might lose the function on the sorting pathway of both proteins within ER lumen at the downstream of esp2.

Prolamins are accumulated in the protein body (PB) I derived from ER, while glutelins are accumulated in the PBII derived from vacuole.

The immunocytochemical analysis of developing endosperm cell in glup6 mutant demonstrated that there were mutant type PB derived from ER exhibiting irregular surface with peripheral region which were labeled by not only the antibodies against prolamin but also that against Alpha glutelin (Fig 1.B).

These observation suggest that the product of glup6 gene involves in segregation of proglutelins and prolamins within ER lumen. However, the chromosome location of glup6 was not known. In this study linkage analysis by using PCR marker was carried out and it revealed that glup6 was located on chromosome 3. Further, to identify and isolate the key gene involved in glup6 mutation, we constructed the linkage map of Glup6 gene on chromosome 3. A glup6 mutant line, EM939, induced from a japonica rice variety Taichung65 by MNU treatment, was crossed with an indica rice variety Kasalath. Method of screening glup6 homozygous was refered to Sato et al. (2003). F₂ analysis using 41 glup6 homozygous F₂ plants showed that the glup6 gene was mapped within 10.4 cM region between PCR markers, R10784 and R216 on Chromosome 3 (Fig. 2).

This study was partly supported by Bio-oriented Technology Research Advancement

Institution (BRAIN), Japan.

References

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Satoh, H., W.X. Li, Y. Takemoto, T. Ito, T. Kumamaru, L. Q. Qu and M. Ogawa, 1999. glup 4 gene controlling a 57H character was located on chromosome 12 in rice. RGN 16: 98-100.

Satoh, H., T. Kumamaru, S.Yoshimura, M. Ogawa, 1994. New 57 kDa glutelin genes on chromosome 9 in rice. RGN 11: 158-161.

Sato, M., Y. Takemoto, T. KUMAMARU, and H. SATOH, 2003. Mapping of Glup4 gene for glutelin precursor increased mutant in rice. RGN 20 (submitted).

Takemoto, Y., Sean J. Coughlan, T. W. Okita, H. Satoh, M. Ogawa, and T Kumamaru, 2002. The rice mutant esp2 greatly accumulates the glutelin precursor and deletes the protein disulfide isomerase. Plant Cell Physiol. 128: 1212-1222.

Tian H.D., T. Kumamaru, Y. Takemoto, M. Ogawa and H. Satoh, 2001. Gene analysis of new 57H mutant gene, glup6, in rice. RGN 18: 48-50.