Mutants are one of the useful tools elucidating the genetic mechanism involving in above events. 57H mutants are characterized by the increased amount of proglutelin with an apparent molecular size of 57 kD while amount of mature glutelin subunits decrease (Kumamaru et al. 1988). Biochemical and histochemical analysis of these 57H mutants indicated that 57H mutations are caused by the lesion of genes encoding respective factors involving in the events from the translation of glutelin mRNA to the deposition in protein storage vacuole (Takemoto et al. 2002). So far 110 independent 57H mutants were isolated by MNU treatment and seven independent gene loci, that is, esp2, Glup1 to glup6 involving in 57H mutation have been identified (Tian et al. 2001). In this report, we describe a novel gene glup7 for 57H mutation.

A kind of 57H mutant, CM935 was derived from the MNU treatment of a rice cultivar Kinmaze (Kumamaru et al., 1988). The seed storage protein of this mutant was characterized by the abnormal accumulation of 57kD proglutelin with less amount of both of acidic and basic mature glutelin in addition to decreased amount of 26kD salt soluble protein (Fig. 1). The prolamin seed storage proteins were less affected by this mutation. The grain did not exhibit any aberration in appearance. F₁ seeds derived from crosses between Kinmaze and CM 935 showed the normal phenotype in the SDS-PAGE profiles of seed storage protein. The ratio of normal to 57H mutant in the F₂ seeds was 3:1 that fitted well to the expected ratio of single recessive inheritance, indicating that the 57H mutation in CM935 is controlled by a single recessive gene (Table 1).

Recombinants exhibiting the normal phenotype segregated in all of F2s derived from crosses between CM935 and each of marker lines for 7 kinds of 57H mutant genes (Table 1), indicating that the 57H mutant gene of CM935 is independent from other seven 57H mutant genes. glup7 was named to the gene of 57H mutation in CM935 from these results. F₂ seeds from the cross of glup7with esp2 segregated into a ratio of 9 (normal): 3 (glup7): 4 (esp2) without double mutant type, suggesting that esp2 gene is epistatic to glup7 gene. Similar segregation modes were observed in F₂s from cross combinations between glup7and glup4 and between glup7and glup6, suggesting that glup4 and glup6 are epistatic to glup7. Glup5 is an incomplete dominant gene and shows the dosage effect in the proglutelin accumulation. In F₂s derived from a cross combination of glup7 with Glup5, the segregation of both mutant types fitted the expected ratio of 3 (normal): 4 (Glup5): 1 (glup7), suggesting that Glup5 is also epistatic to glup7. Although double mutant types being higher in proglutelin content than both of paren-

tal lines were not found in crosses between glup7 and glup3, novel types being intermediate in the proglutelin content between glup7 and glup3 were detected. The segregation mode fitted well the expected ratio of 9 (normal): 3 (glup7): 1 (Int): 3 (glup3), suggesting that glup7 affects to be epstatic to glup3 and suppresses the proglutelin accumulation in glup3 mutation. In the cross combinations of glup7 with Glup1 and glup2, double mutant types were detected, indicating that they have the additive effect on proglutelin accumulation each other.

Trisomic segregation for glup7 was found in F₂ seeds from the self-pollinated trisomic F₁ plant of a cross between Triplo4 having extra chromosome 4 and CM935, while disomic segregation was observed in F₂s from crosses combination of CM935 with other eight trisomic lines (Table 3). These results suggest that a gene Glup7 locates on chromosome 4.

Acknowledgement

This work was supported by the Ministry of Education, Science and Culture of Japan (Grant no. 12138506) and BRAIN.

Reference

Kumamaru, T., H. Satoh, N. Iwata, T. Omura, M. Ogawa and K. Tanaka, 1988. Mutants for rice storage proteins 1. Screening of mutants for rice storage proteins of protein bodies in the starchy endosperm. Theor. Appl. Genet. 76, 11-16.

Takemoto, Y., S.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 isomers. Plant Physiol. 128, 1212-1222.

Tian, H.D., T. Kumamaru, Y. Takemoto, M. Ogawa and H. Satoh, 2001. Gene analysis of a new 57H mutant gene, glup6, in rice. RGN 18: 48-49.