Complex organization of the rice Purple leaf locus involved in tissue-specific accumulation of anthocyanin

摘要

The Purple leaf (PI) locus of rice affects the regulation of anthocyanin biosynthesis in various tissues. Tissue-specific patterns of anthocyanin pigmentation, together with the syntenic relationship, suggest that rice PI may be orthologous to maize B. We isolated two cDNAs, OSB1 and OS82, by screening a library prepared from PF plants using maize 8 as a probe. The two cDNAs showed the significant identity of the basic helix-loop-helix (bHLH) myc-type proteins found in the maize R/B gene family. Several lines of evidence suggest that OS61 and OS82 compose the Pl~w alleie. First, both genes were expressed in a near-isogenic line, T65-Plw, but not in parental line T65, Second, all the PI alleles examined accumulated either one or both of the OS81 andOS82 transcripts. Third, both OS81 and OS82 genetically cosegregated with each other and the PP genotype. Finally, anthocyanin synthesis was activated by the ectopic expression of these two cDNAs, showing that proteins encoded in OS8I and OSB2 likely actas a transcriptionai activator in vivo. Possible allelic diversity among the PI alleles was comparable to some alleles of the R gene in maize, suggesting that tissue-specific anthocyanin accumulation is controlled by a similar mechanism in rice and maize, but the organization of the responsible genes appears to be diverse between the two species.