[Screening and genetic analysis of rice glutelin mutant]

The contribution of rice as a protein source is important. Rice seed protein can be divided into four forms, glutelin (57 kDa, 37-39 kDa, 22-23 kDa), prolamine (13 kDa), albumin (16 kDa) and globulin (10 kDa, 26 kDa) on its solubility. Glutelin is the major storage protein of rice and accounted for 80% of total protein found in the rice grain, the mature glutelin comprises an acidic (37-39 kDa) and an basic subunit (22-23 kDa) coming from a common precursor (57 kDa) by post-transcriptional hydrolytic cleavage. Prolamine is the second important. Rice seed proteins localize in two types of protein bodies, PB-I, PB-II. PB-I containing prolamine is indigestible, whereas PB-II being rich in glutelin is digestible. The nutritional value of rice could thus be raised by improving its digestible protein glutelin content. On the other hand, the character of low digestible protein is also an important target of rice breeding. Low protein rice is required for the diet of patients with kidney disease. Three glutelin mutants, W3660, W204, W379, were found by screening 168 rice varieties through SDS-PAGE analysis of the seeds total proteins. The amounts of 37-39 kDa and 22-23 kDa glutelin subunits were much lower and that of 13 kDa prolamine polypeptide was higher in W3660 seeds than in ordinary rice; The amounts of 37-39 kDa and 22-23 kDa glutelin subunits in W204 or W379 seeds were between those in W3660 and ordinary rice. Especially, in W379 seed, there was a large quantity of 57 kDa polypeptide. For characterizing the genetics of the glutelin mutant, the cross population between W3660 and Otorokimochi was constructed. SDS-PAGE analysis of the progeny seed total proteins showed, low glutelin content was always accompanied by high prolamine content; all F1 seeds had low glutelin and high prolamine content; the segregation of low glutelin and normal type in F2 seeds was 3:1; the genotypes of F2 plants were deduced by the analysis of F3 seeds, and among F2 plants the ratio of homozygotes of low glutelin, heterozygotes of low glutelin and homozygotes of normal type was about 1:2:1. These results proved that the trait of low glutelin and high prolamine was controlled by a single dominant gene and could be inherited by its progeny.