It is generally accepted that anthocyanin coloration plays an important role not only for the elucidation of gene regulation and character expression in plant metabolism but also provides side effects for the tolerance to biotic and abiotic stresses. The regulatory genes for maize anthcyanin were found to encode the transcriptional factors and are divided into myb(Cl/Pl) and myc(B/R) families. The molecular basis for tissue-specificity (Radicella el al. 1992), paramutation (Patterson et al. 1995) and evolutionary aspects (Hanson et al. 1996) have been investigated thoroughly in anthocyanin pigmentation in maize. Furthermore, based on synteny map between maize and rice (Ahn and Tanksley 1993), evolutionary pathways of regulatory genes for anthocyanin pigmentation are discussed in Poaceae including rice (Purugganan and Wessler 1994; Hu et al. 1996). Therefore, it is important to investigate the regulatory network for anthocyanin pigmentation.

In rice, chromosome 4 has many regulatory genes for anthocyanin pigmentation, such as Pi, pl-2, Prp, P, Pr, Ps-I, Ps-2 and Pin-1 (Kinoshita 1995). Sanchez and Khush (1994) found a recessive gene for purple leaf and named it pl-2. It is already known that several inhibitors exist for the coloration of leaf blade and l-pl-6 has a strong effect in inhibiting the whole coloration due to Pl' showing the coloration as a recessive charactor. As pl-2 is located on chromosome 4, it is necessary to investigate the allelic relation between pl-2 and Pi' under the existence of l-Pl-6. Further, Xie et al. (1995) indicated unstable purple-red hull trait (PRH) which was induced by somaclonal mutation. PRH controlled by a single dominant gene is closely linked with the purple apiculus character which was also induced in the original somaclone. On chromosome 4, purple hull gene, Pr and colored apiculus gene, P are linked with 13cM (Kinoshita 1995). So, there is a possibility that somaclonal mutaions occurred simultaneously at Pr and P loci. Reddy et al. (1995) pointed out the presence of the dominant inhibitor (Ilb) for leaf coloration due to Pl ^w. Reddy et al. (1994) identified cyanidin and peonidin as a major and minor pigments of anthocyanin, respectively, and suggested that UV-B irradiation activates Pl^w, resulting in anthocyanin induction. They also demonstrated that UV-B-triggered anthocyanin induction is reduced by a terminal far-red light pulse and is recovered by a red light pulse. On the other hand, brown pericarp controlled by Rc and Rd contains proanthocyanidins which are produced by a blockage in the anthocyanin biosynthetic pathway at the anthocyanidin synthase-mediated conversion of leucoanthocyanidin to anthocyanidin (Reddy et al. 1995). Hu et al. (1996) isolated Ra and Rb genes which are located on Chromosome 4 and I, respectively from Purple 522

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strain. Transient assay of Ra using imbibed maize kernels demonstrated that Ra activate the anthocyanin pathway of maize, suggesting that Ra is the candidate of Pl allele. It is inferred that the reddish brown rice is expressed by a pleiotropic effect of leaf color gene Pl^w when it co-exists with C (Chromogen) in the absence of A (Anthocyanin activator) and Rc and Rd constitute another pathway (Kinoshita 1984). (Gene symbol: Old system)

References 

Ahn, S. and S.D. Tanksley, 1993. Comparative linkage maps of the rice and maize genomes. Proc. Natl.

Acad. Sci. 90:7980-7984.

Chandler, V.L., J.P. Radicella, T.P. Robbins, J. Chen and D. Turks, 1989. Two regulatory genes of the maize anthocyanin pathway are homologous: isolation of B utilizing R genomic sequences. Plant Cell 1: 1175-1183.

Dellaporta, S.L., 1. Greenblatt, J. Kermicle, J.B. Hicks and S.R. Wessler, 1988. Molecular cloning of the maize R-nj allele by transpozon tagging with Ac. In Chromosome Structure and Function: Impact of New Concepts, 18th Stadler Genetics Symposium, eds. Gustafson, J.P. and R. Appels (Plenum, New York), pp. 263-282.

Hanson, M.A., B.S. Gaut, A.O. Stec, S.I. Fuerstenberg, M.J. Goodman, E.H. Coe and J.F. Doebly, 1996. Evolution of anthocyanin biosynthesis in maize kernels: the role of regulatory and enzymatic loci. Genet. 143:1395-1407.

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9-153.

Ludwig, S.R., L.F. Habera, S.L. Dellaporta and S.R. Wessler, 1989. Lc, a member of the maize R gene family responsible for tissue specific anthocyanin production, encodes a protein similar to transcriptional activators and contains the myc-homology region. Proc. Natl. Acad. Sci. 86: 7092-7096.

Patterson, G.I., K.M. Kubo, T. Shroyer and V.L. Chandler, 1995. Sequences required for paramutation of the maize b gene map to a region containing the promoter and upstream sequences. Genet. 140: 1389-1406.

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Radicella, J.P., D. Brown, L.A. Tolar and V.L. Chandler, 1992. Allelic diversity of the maize B regulatory gene: different leader and promoter sequences of two B alleles determine distinct tissue specificities of anthocyanin production. Genes & Dev. 6: 2152-2164.

Reddy, V.S., K.V. Goud, R. Sharma and A.R. Reddy, 1994. Ultraviolet-B-responsive anthocyanin production in a rice cultivar is associated with a specific phase of phenylalanine ammonia lyase biosynthesis. Plant Physiol. 105:1059-1066.

Reddy, V.S., S. Dash and A.R. Reddy, 1995. Anthocyanin pathway in rice (Oryza sativa L.): identification of a mutant showing dominant inhibition of anthocyanins in leaf and accumulation of proanthocyanidins in pericarp. Theor Appl Genet 91: 301-312.

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