LIGHT INDUCIBILITY AND TISSUE-SPECIFICITY OF THE R-GENE FAMILY IN MAIZE

The red and purple anthocyanin pigments of plants are visible genetic markers and their spatial and temporal accumulation is strictly regulated. Anthocyanin biosynthesis is also modulated by environmental factors such as light and temperature. Thus this process represents an appealing model system for the study of gene regulation, as well as for studying developmental biology. In maize, the pattern of pigmentation of the plant is controlled by the R, Sn and B genes, a small family of HLH transcription factors. Here we report the pattern of light induction and tissue specific expression of the regulatory and structural genes involved in this biosynthesis. Two Sn alleles differing in their light response have been considered and analyzed by Northern and in situ hybridization experiments. An unusual phenomenon of interaction between the homologous R and Sn genes leading to a partial gene silencing is reported. We hypothesize a model in which silencing is achieved through methylation of specific sites.