A cluster of Arabidopsis genes with a coordinate response to an environmental stimulus.

Vernalization, the promotion of flowering after prolonged exposure to low temperatures, is an adaptive response of plants ensuring that flowering occurs at a propitious time in the annual seasonal cycle. In Arabidopsis, FLOWERING LOCUS C (FLC), which encodes a repressor of flowering, is a key gene in the vernalization response; plants with high-FLC expression respond to vernalization by downregulating FLC and thereby flowering at an earlier time. Vernalization has the hallmarks of an epigenetically regulated process. The downregulation of FLC by low temperatures is maintained throughout vegetative development but is reset at each generation. During our study of vernalization, we have found that a small gene cluster, including FLC and its two flanking genes, is coordinately regulated in response to genetic modifiers, to the environmental stimulus of vernalization, and in plants with low levels of DNA methylation. Genes encoded on foreign DNA inserted into the cluster also acquire the low-temperature response. At other chromosomal locations, FLC maintains its response to vernalization and imposes a parallel response on a flanking gene. This suggests that FLC contains sequences that confer changes in gene expression extending beyond FLC itself, perhaps through chromatin modification.