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

In plants, transgenes often induce rapid turnover of homologous endoge nous transcripts. This ''cosuppression'' of homologous genes is an ext remely nonlinear response to small increases in gene expression or dos age, inversely amplifying them into dramatic phenotypic alterations. P igment transgenes elicit metastable cosuppression patterns organized b y flower morphology. Pattern organization and metastability reflect re gulatory states (probably transgene transcription states) that respond to morphological features and are labile to physiology and developmen t. 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 gr owth.