Conserved RY-repeats mediate transactivation of seed-specific promoters by the developmental regulator PvALF

Transcription of genes DLEC2 and PHSbeta is specifically and coordinately regulated during maturation of Phaseolus embryos. Over-expression of the seed- specific factor PvALF in cotyledon cells results in transactivation of either promoter. PvALF is related to the VP1 protein of maize, which transactivates gene expression via G-boxes, Sph elements and AT-rich sequences. We used deletions and base substitutions in the DLEC2 and PHSbeta promoters to demonstrate that several conserved RY-repeats were necessary for PvALF induction of both genes. A comprehensive mutational and transactivation analysis was used to define functionally the sequence of the DLEC2 repeat RY3 asG/CCATGCxxG/C. We also found that an interaction between RY3 and the 3'-flanking tetranucleotide CCAC increased PvALF transactivation. A preferred spacing and phasing requirement for the RY3 and CCAC motifs suggested the possibility of interactions between cellular factors that recognize either element. The high conservation of Sph-RY motifs in seed-specific promoters from monocots and dicots indicates that organ and temporal specification by factors similar to VP1 and PvALF is common among seed plants.