The two genes, C (chromogen for anthocyanin) and A (anthocyanin
activator) are known to be basic genes for forming anthocyanin pigment
in different organs of rice, and P (colored apiculus) is also essential
for the pigmentation in the apiculus (Takahashi 1957, 1982). Series of
multiple alleles at these loci, especially at the C locus, contribute
varying degrees of apiculus coloration and some alleles at the C
locus are responsible for so called tawny color without the A (Takahashi
1982). In addition, the genetic diversity for anthocyanin pigmentation
seems to be higher in cultivated rice than the wild progenitors (Oka 1989).
We intend to investigate the allelic differentiation at the C locus
in order to understand the genetic diversity preserved in cultivated rice.
The C locus is located on the short arm of chromosome 6 and is
linked to the wx which also shows allelic differentiation among
rice cultivars. Based on synteny of maps between rice and maize, the region
including these genes is present on chromosome 9 of maize and the maize
C1 anthocyanin regulatory gene is located in the region. The C1
encodes a MYB like protein factor which activates the transcription of
a number of structural genes involved in anthocyanin pigment biosynthetic
pathway (Paz-Ares et al. 1987). The rice homologue (Os-C1)
of the maize C1 was cloned from cDNA library of Purpleputtu seedlings
(Reddy et al. 1998). The present study was carried out to compare
the genomic sequences of the Os-C1 of tawny-colored (T65wx,
Japonica type) and colorless (IR36 and Patpaku, Indica type) lines. DNA
fragments were amplified with PCR and were sequenced, showing the presence
of three exons as expected. The results revealed that the two colorless
lines had a 10-bp deletion and T65wx had a non-synonymous substitution
in the 3rd exon, when compared with the OsC1 from Purpleputtu.
This suggested that the deletion might be responsible for colorless apiculus
since the two colorless lines had the same deletion. Regarding the location
of the Os-C1, 5 NILs which carried different segments of chromosome
6 from Patpaku were examined. Comparisons by sequencing revealed that
2 colorless NILs (A and D) had a 10-bp deletion and 3 colored
G and I) had the same sequence as that of T65wx (Fig. 1). This
indicates that the difference in the Os-C1 is related to the phenotype
for apiculus coloration and the Os-C1 is located on chromosome
To locate the Os-C1 precisely, 67 F2 plants of T65wx
x IR36 were analyzed using RFLP markers on the short arm of chromosome
6. The 10-bp deletion in the 3rd exon was analyzed with PCR products using
primers of #3 and #4 (Fig. 1) which were separated on 5% acrylamide gel.
The difference in fragment size was easily detected and the heterozygotes
showed two-bands. The Os-C1 was linked to RZ588 marker with map
distance of 6.2 cM and was located between RZ588 and G200. It was also
linked to the wx with 27.1 cM which was consistent with the recombination
value reported in Indica-Japonica crosses (Oka 1989), suggesting that
the Os-C1 is a candidate for the C although further studies are
needed. Comparisons of the Os-C1 among lines with different alleles
at the C locus are now in progress.
Oka, H.I., 1989. Distribution of gene diversity in Indica and Japonica
rice varieties and their wild progenitors. RGN 6: 70-71.
Paz-Aryes, J., D. Ghosal, U. Wienand, P.A. Peterson and H. Saedler, 1987.
The regulatory c1 locus of Zea mays encodes a protein with
homology to myb proto-oncogene products and with structural similarities
to transcriptional activators. EMBO J. 6: 3553-3558.
Reddy, V.S., B.E. Scheffler, U. Wienand, S.R. Wessler and A.R. Reddy,
1998. Cloning and characterization of the rice homologue of the maize
C1 anthocyanin regulatory gene. Plant Mol. Biol. 36: 497-498.
Takahashi, M.-E., 1957. Analysis on apiculus color genes essential to
anthocyanin coloration in rice. J. Fac. Agr. Hokkaido Univ., 50:
Takahashi, M.-E., 1982. Gene analysis and its related problems. J. Fac.
Agr. Hokkaido Univ., 61: 91-142.