1. Gene symbols for endosperm traits

Hikaru Satoh1 and Etsuo Amano2

1) Faculty of Agriculture, Kyushu University, Higashi-ku, Fukuoka, 812 Japan

2) Institute of Radiation Breeding, MAFF, P. 0. Box 3, Ohmiya-machi, lbaraki-ken, 319-22 Japan

A number of genic mutations for morphological and biochemical properties of rice endosperm have been obtained recently. With the increase in the number of such mutants, some confusion may occur in the names and symbols of these mutant genes, which describe the kernel phenotypes. Some endosperm genes are described by such characters as particular protein fractions or carbohydrate fractions produced by them. The genes so far reported for endosperm traits in rice are listed in Table 1.

The endosperm mutant genes which alter carbohydrate fraction of starch are:

Table 1.  List of genes for endosperm traits
______________________________________________________________
Gene   Name            Phenotype          Chromo-        Remark
symbol                                    some
______________________________________________________________
ae     amylose     floury to translucent  unknown
       extender    endosperm,high amylose 
                   content
alk    alkali      endosperm starch less-    6
       digestion   resistant to alkali 
                   digestion
du-1   dull endo-  glassy and tarnished      7
       sperm-1     endosperm,low amylose 
                   content
du-2   dull endo-  like du-I but the amylose 1(?)
       sperm-2     content slightly higher
du-3   dull endo-  like   du-1            unknown
       sperm-3
du-4   dull endo-  like   du-1               4(?)
       sperm-4
du-5   dull endo-  like   du-1            unknown
       sperm-5
flo-1  floury end- opaque and soft           5(?)
       osperm-1    endosperm
flo-2  floury end- like  flo-1               2
       osperm-2
flo-3  floury end- like  flo-1              11
       osperm-3
ge     giant       larger size of embryo    10
       embryo
esp-1  endosperm   decreased 13kD-b         10
       storage     polypeptide
       protein-1
esp-2  endosperm   increased 57kD            9
       storage     polypeptide               
       protein-2 
shr-1  shrunken    shrunken and opaque to    3    shr-1s shr-
       endosperm   translucent endosperm,         1a(multiple   
        -1         sugars rich                      alleles)
shr-2  shrunken    like shr-1               12
       endosperm
        -2
sug    sugary      endosperm wrinkled and   12
       endosperm   glassy when dry. high 
                   WSP content
wx     glutinous   opaque and hard endo      6    Wxa, Wxb  
       endosperm   sperm, low or no               wxa  
                   amylose content
______________________________________________________________
amylose extender (ae), dull endosperm (du-1, du-2, du-3, du-4, and du-5), shrunken endosperm (shr-1 and shr-2), sugary endosperm (sug), and glutinous endosperm (wx). The kernels of ae mutant are opaque to translucent. The endosperm starch is characterized by an increased amount of amylose, the B type of X-ray diffractgram, a high gelatinization temperature, and the production of longer unit chains of amylopectin (Yano et al. 1985). As these characteristics are similar to those of the amylose extender mutant (ae) of maize, symbol ae is assigned to the gene for this mutant trait. The location of ae still remains unknown.

Some mutants with lowered amylose content in endosperm starch have been obtained through induced mutations (Toda 1979; Okuno et al. 1983; Omura and Satoh 1984) or from spontaneous origins (IRRI 1975; Nakagahra et al. 1986). The endosperms of these mutants become dull after drying, showing an inter- mediate appearance between glutinous rice and non-glutinous rice. Therefore, these mutants are designated as "dull" and a series of genes controlling this trait are symbolized du. Yano (1985) reported that there were at least five different gene loci for this trait based on the allelism tests among various dull mutants. One of them, du-1, was located on chromosome 7. The recessive gene for the glutinous endosperm is customarily symbolized wx (waxy, although there is no wax); other symbols like m (mochi), am (amyloseless), gl or g (glutinous endosperm) for this locus were used in the past (Kihara 1964). Alleles identified at the Wx locus include Wxa for low amylose content (Yano 1985) and a number of recombinationally distinct alleles (Sakai et al. 1987). In addition, Sano et al. (1986) reported that the difference in amylose content of non-glutinous rices of Indica and Japonica types was controlled by co-dominant alleles at this locus, Wxa and Wxb.

Two types of mutants for wrinkled grain shape exhibiting similar phenotypes and chemical properties as of sugary 1 and shrunken-2 of maize, respectively, were found in rice (Satoh and Omura 1981). The two mutants were then named "sugary" and "shrunken" and the genes were symbolized sug,and shr, respectively. The endosperm of the shrunken type is collapsed and opaque. Two loci, shr-1 and shr-2, were identified for this trait. The shr-1 locus had two alleles, shr-1s and shr-1a, the former being dominant over the latter (Yano et al. 1984). Gene shr-1 is linked with marker genes, rl-2, A, lax and d-10, located on chromosome 3 (Yano et al. 1984; Matsuo et al. 1986). Matsuo et al. (1986) reported that shr-2 was located on chromosome 12.

The endosperm of sugary type mutants is wrinkled and glassy with light brown or amber color, and is characterized by an increased amount of water soluble polysaccharides and a decreased amount of starch (Omura and Satoh 1984). Gene symbol sug is assigned to this mutant instead of su, since Su was already adopted for the suppressor for long sterile lemmas (Nagao et al. 1960). Gene sug is located on chromosome 12 (Iwata et al. 1984).

Kudo (1968) described gene alk which controlled the alkali digestion of endosperm starch and was linked with wx in lankage group I.

Gene symbol esp (endosperm storage protein) may be assigned to mutant traits for storage protein in the endosperm. Kumamaru et al. (1986) found four types of mutants for storage protein and located them on different chromosomes. Gene esp-1 which accounts for the 13 kD-b polypeptide accumulation was located on chromosome 1O, and esp-2 which effects the 57 kD polypeptide accumulation, was located on chromosome 9 (Kumamaru et al. 1987).

Satoh and Omura (1981) described some gene mutations which brought about an opaque appearance of the endosperm. They were classified according to kernel morphology into "floury", "white core", "opaque kernel", etc., although the classification was somewhat arbitrary. Most of them were controlled by a single recessive gene with the exception of the floury mutant which was controlled by duplicate recessive genes. Gene symbol flo is used for the gene governing the floury mutants whose endosperm is soft and chalky. There are at least three different gene loci for this trait (Maekawa 1986; Satoh 1985).

Mutations for the size and morphology of embryo were found by Satoh and Omura (1981) and Yoon (1985). Yano et al. (1980) reported that a recessive gene, ge, expressing larger embryo size named "giant embryo" was located on chromosome 10.

References

IRRI, 1975. Annual Report, p. 85-86.

Iwata, N., H. Satoh and T. Omura, 1984. Relationship between the twelve chromosomes and linkage groups (Studies on the trisomics in rice plants (Oryza sativa L.)) Jpn. J. Breed. 34:314-321.

Kudo, K., 1968. Genetical and breeding studies on physiological and ecological characters in hybrids between ecological groups of rice. Bull. Nat. Inst. Agr., Sci. Ser. D19: 1-84.

Kumamaru, T., H. Satoh, N. Iwata, T. Omura and M. Ogawa, 1986. Mutants affecting storage protein in rice seed. RGN 3: 101-103.

Kumamaru, K., M. Yamamoto, H. Satoh, N. lwata, T. Omura, M. Ogawa and K. Tanaka, 1987. Genetic analysis of mutants for storage protein in rice endosperm. Jpn. J. Breed. 37 (Suppl. 1): 336-337.

Maekawa, M., 1985. Location of a floury endosperm gene in the second linkage group. RGN 2:57-58.

Matsuo, T., M. Yano, H. Satoh and T. Omura, 1986. Location of gene shr-1 on chromosome 3. RGN 3: 60-61.

Matsuo, T., M. Yano, H. Satoh, N. Iwata and T. Omura, 1986. Gene shr-2 located on chromosome 12. RGN 3: 61-62.

Matsuo, T., H. Satoh and T. Omura, 1987. Newly obtained mutants of shrunken and sugary in rice. Jpn. J. Breed. 37 (Suppl. 1): 204-205.

Nagao, S., M. Takahashi and T. Kinoshita, 1960. Genetic studies on rice plant XXV. Inheritance of three morphological characters, pubescence of leaves and floral glumes, and deformation of empty glumes. J. Fac. Agr., Hokkaido Univ. 51: 299-314.

Nakagahara, M., T. Nagamine and K. Okuno, 1986. Spontaneous occurence of low amylose genes and geographycal distribution of amylose content in Asian rice, RGN 3: 46-48.

Okuno, K., H. Fuwa and M. Yano, 1983. A new mutant gene lowering amylose content in endosperm starch of rice, Oryza sativa L. Jpn. J. Breed. 33: 387-394.

Omura, T. and H. Satoh, 1984. Mutation of grain properties in rice. In S. Tsunoda and N. Takahashi (eds.), "Biology of Rice", pp. 293-303. Japan Sci. Press, Tokyo/Elsevier, Amsterdam.

Sakai, A., M. Yano, H. Satoh, N. lwata and T. Omura, 1987. Intragenic analysis of waxy mutants in rice. Jpn. J. Breed. 37 (Suppl. 1): 162-163.

Sano, Y., M. Katsumata and K. Okuno, 1986. Genetic studies of speciation in cultivated rice. 5. Inter- and intraspecific differentiation in the waxy gene expression of rice. Euphytica 35:1-9.

Satoh, H., 1985. Genic mutations affecting endosperm properties in rice. Gamma Field Symp.24: 17-37.

Satoh, H. and T. Omura, 1981. New endosperm mutations induced by chemical mutagens in rice,Oryza sativa L. Jpn. J. Breed. 31: 316-326.

Toda, M., 1979.Breeding of new varieties by gamma-rays. Gamma Field Symp. 18: 73-82.

Yano, M., 1985. Genetical and plant breeding studies on the mutant of amylose content in endosperm starch of rice. Ph. D. Thesis Kyushu University.

Yano, M., H. Satoh and T. Omura, 1980. Gene analysis on the endosperm mutants induced by MNU treatment in rice. Jpn. J. Breed. 30 (Suppl. I): 260-261.

Yano, M., Y. Isono, H. Satoh and T. Omura, 1984. Gene analysis of sugary and shrunken mutants of rice, Oryza sativa L. Jpn. J. Breed. 34: 43-49.

Yano,M., K. Okuno, J. Kawakami, H. Satoh and T. Omura, 1985. High amylose mutants of rice, Oryza sativa L. Theor. Appl. Genet. 69: 253-257.