EMBRYONIC FLOWER2, a novel polycomb group protein homolog, mediates shoot development and flowering in Arabidopsis

In higher plants, developmental phase changes are regulated by a complex ge ne network. Loss-of-function mutations in the EMBRYONIC FLOWER genes (EMF1 and EMF2) cause Arabidopsis to flower directly, bypassing vegetative shoot growth. This phenotype suggests that the EMF genes play a major role in rep ression of the reproductive program. Positional cloning of EMF2 revealed th at it encodes a zinc finger protein similar to FERTILIZATION-INDEPENDENT SE ED2 and VERNALIZATION2 of Arabidopsis. These genes are characterized as str uctural homologs of Suppressor of zeste 12 [Su(z)12], a novel Polycomb grou p gene currently identified in Drosophila. In situ hybridization studies ha ve demonstrated that EMF2 RNA is found in developing embryos, in both the v egetative and the reproductive shoot meristems, and in lateral organ primor dia. Transgenic suppression of EMF2 produced a spectrum of early-flowering phenotypes, including emf2 mutant-like phenotype. This result confirms the role of EMF2 in phase transitions by repressing reproductive development.