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New rice cultivars with low levels of easy-to-digest protein

Minoru Nishimura,1 Makoto Kusaba,1 Kenzo Miyahara,1 Takeshi Nishio,2 Shuich Iida,3 Tokio Imbe,4 Hiroyuki Sato4

1 National Institute of Agrobiological Sciences Regional Institute, Omiya-machi, Naka-gun, Ibaraki 319-2293, Japan, Email:
Graduate School of Agricultural Science, Faculty of Agriculture, Tohoku University, Sendai 981-8555, Japan
National Agricultural Research Center for Western Region, Fukuyama, Hiroshima 721-8514, Japan
National Institute of Crop Science, Tukuba, Ibaraki 305-8518, Japan


Rice seed contains 2 major proteins: glutelin and prolamine. Glutelin accumulates in protein body type II (PB-II), and prolamine in PB-I. PB-II is easily digested by humans, but PB-I is indigestible. We previously developed a new rice cultivar, LGC1, from ‘Nihonmasari’ by means of ethyleneimine treatment. LGC1 seed contains low levels of glutelin and high levels of prolamine. This makes LGC1 suitable for use by patients with chronic renal failure, even though the total protein content is nearly the same as in the original cultivar. In the present study, we bred 2 new cultivars from a cross between LGC1 and a mutant line of ‘Koshihikari’ that is deficient in 26-kDa globulin. Their glutelin content is about 1/3 of that of regular cultivars, and they completely lack 26-kDa globulin. Overall, these cultivars have about half the easy-to-digest protein content of regular cultivars. They are thus even more suitable for use in a low-protein diet than LGC1.

Media summary

New rice cultivars with a low content of easy-to-digest protein were developed. They are suitable for patients with kidney disease.

Key words

diet therapy, dietary food, endosperm, mutation breeding, Oryza sativa


In Japan, the steep rise of medical expenses has become an object of public concern, particularly because the population is aging. In particular, the cost of blood dialysis is a very important issue for patients with kidney disease. About 15,000 new patients a year are enrolled for blood dialysis therapy, and the total patient population is about 200,000. About 500,000 people manage chronic renal failure without blood dialysis through therapy based on a low-protein diet. They require specially processed low-protein foods. The use of hyper-polished rice or starch rice is the main method of restricting their intake of protein, but these products are very expensive compared with ordinary rice. Rice cultivars with low protein content would offer a cheaper diet.

Usually, rice seed contains about 7% protein, and rice supplies about 15% of the average dietary intake of protein in Japan. Rice seed contains 2 major proteins: glutelin and prolamine. Glutelin accumulates in protein body type II (PB-II), and prolamine in PB-I (Tanaka et al., 1980). PB-II is easily digested, but PB-I is indigestible (Ogawa et al., 1987). Through the use of mutation breeding, we developed a new cultivar, LGC1, from ‘Nihonmasari’, with a low glutelin and high prolamine content (Iida et al., 1993). Glutelin is synthesized as a 57-kDa precursor and then cleaved into a 37- to 39-kDa acidic subunit and a 22- to 23-kDa basic subunit. The glutelin content of LGC1 is reduced and the contents of other storage proteins, including prolamine, are increased compared with more common rice cultivars (Iida et al., 1993). Because of the indigestibility of prolamine, LGC1 can be used as a low-protein rice. It is thus useful for people who must restrict their protein intake, such as patients with kidney disease (Mochizuki and Hara, 2000).

The molecular characterization of Low glutelin content 1 (Lgc1) has been recently reported. Lgc1 is a dominant mutation that suppresses expression of the glutelin multigene family. It causes a 3.5-kb deletion between 2 GluB genes that form a tail-to-tail inverted molecule, which is thought to be a trigger for post-transcriptional gene scilencing (PTGS) (Kusaba et al., 2003). It is very rare for a single study to simultaneously reveal both the molecular characterization of a gene and its use.

The content of easy-to-digest protein in LGC1 is about 2/3 that of ordinary cultivars. But there is room to further decrease the content, because levels of the 26-kDa globulin in LGC1 are slightly increased compared with ordinary cultivars. Fortunately, a mutant that is deficient in 26-kDa globulin is available (Iida et al., 1998). In the present study, we aimed to combine the traits of LGC1 and the mutant.


We developed 2 new rice cultivars from a cross between LGC1 and a mutant line of Koshihikari (89WPKG30-433) that is deficient in 26-kDa globulin. Both have a low content of easy-to-digest protein and are nonglutinous: LGC-Katsu is early-maturing and LGC-Jun is intermediate-maturing. (Katsu means vigorous and Jun means warm-hearted in Japanese.) After testing for local adaptability, specific characters, yield, and dietary performance, they were registered with the Japanese Ministry of Agriculture, Forestry and Fisheries.

Results and discussion

The glutelin content of these 2 new cultivars is reduced to about 1/3 that of regular cultivars, and 26-kDa globulin is completely absent. Consequently, the total amount of easy-to-digest protein in the new cultivars is about half that of regular cultivars, and about 15% less than in LGC1. They should thus greatly help in the dietary management of patients with chronic renal failure.

LGC-Katsu matures early, so it can be cultivated in northern Japan, from the Kanto region to the the south of the Tohoku region. However, it is not cool-tolerant at the booting stage, so cultivation should be limited to regions with low risk of cool-weather damage. Because LGC-Jun has a much better eating quality than LGC1, patients should find it easier to eat this cultivar every day. Judging from its maturation date, LGC-Jun can be grown in the plains of southwestern Japan, in the Chugoku, Kinki, Tokai, and Kanto regions. LGC-Jun is intermediate in culm length and a partial panicle number type, has high yield, and is moderately resistant to lodging. Accordingly, the use of nitrogen fertilizer must be restricted in the growing of low-protein rice.

Fig. 1 Genealogy of the new cultivars

Fig. 2 Plant type. (A) From left, Koshihikari, LGC-Katsu, and Shunyo (a new rice cultivar with LGC1-type protein). (B) From left, Koshihikari, LGC-Jun, and LGC1.

Fig. 3 SDS-PAGE analysis of total proteins in brown rice

Table 1. Agronomic characteristics of LGC1, LGC-Katsu, LGC-Jun, and Koshihikari

Cultivar name

Heading date

Culm length

Panicle length

Yield of brown rice (kg/a)

Lodging degree (0 = standing, 5 = lodged)


7 Aug.






30 July






7 Aug.






5 Aug.





Table 2. Nutritional quality of LGC1, LGC-Katsu, LGC-Jun, and Koshihikari

Cultivar name

(% of total protein)

26-kDa globulin (% of total protein)

(% of total protein)

Protein content (% of dry matter)

Easy-to-digest proteina (% of total protein)

Eating quality





























a: Excluding the 13- and 16-kDa proteins.


In the near future, Japan will be home to a huge number of elderly people, many in poor health. The LGC1, LGC-Katsu, and LGC-Jun cultivars have been developed as part of a movement to breed new crop cultivars with functional ingredients that improve human health. In the future, such cultivars will also become useful in other countries.


Iida S, Amano E and Nishio T (1993). A rice (Oryza sativa L.) mutant having a low content of glutelin and a high content of prolamine. Theor. Appl. Genet. 87, 374–378.

Iida S, Miyahara K and Nishio T (1998). Rice mutant lines lacking alpha-globulin. Breed. Sci. 48, 45–49.

Kusaba M, Miyahara K, Iida S, Fukuoka H, Takano T, Sassa H, Nishimura M and Nishio T (2003). Low glutelin content 1: a dominant mutation that suppresses the glutelin multigene family via RNA silencing in rice. The Plant Cell 15, 1455–1467.

Mochizuki T and Hara S (2000). Usefulness of low protein rice in diet therapy in patients with chronic renal failure. Jpn. J. Nephrol. 42, 24–29. (in Japanese with English summary)

Ogawa M, Kumamaru T, Satoh H, Iwata N, Omura T, Kasai Z and Tanaka K (1987). Purification of protein body-I of rice seed and its polypeptide composition. Plant Cell Physiol. 28, 1517–1528.

Tanaka K, Sugimoto T, Ogawa M and Kasa Z (1980). Isolation and characterization of protein bodies in the rice endosperm. Agric. Biol. Chem. 44, 1633–1639.

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