COSUPPRESSION, FLOWER COLOR PATTERNS, AND METASTABLE GENE-EXPRESSION STATES

In plants, transgenes often induce rapid turnover of homologous endogenous transcripts. This ''cosuppression'' of homologous genes is an extremely nonlinear response to small increases in gene expression or dosage, inversely amplifying them into dramatic phenotypic alterations. Pigment transgenes elicit metastable cosuppression patterns organized by flower morphology. Pattern organization and metastability reflect regulatory states (probably transgene transcription states) that respond to morphological features and are labile to physiology and development. Shifts between regulatory states can be highly ordered; for example, a shift may be imposed on a population of cells defining a meristem, which then stably maintains and transmits the new state throughout growth.