Chapter 20: Control of Flowering and Floral Development

The content explores how photoperiodism and vernalization pathways converge through key regulatory genes like FLOWERING LOCUS T and CONSTANS to control the transition from vegetative to reproductive growth. The chapter details the ABC model of floral organ identity, where A-class genes specify sepals and petals, B-class genes determine petals and stamens, and C-class genes control stamens and carpels, with recent expansions to include D and E gene classes for complete floral architecture. Signal transduction pathways involving florigen transport, MADS-box transcription factors, and chromatin remodeling complexes are examined to show how flowering time is precisely controlled. The material covers how circadian clock components interact with light perception systems to measure day length, while vernalization responses involve epigenetic modifications that establish competence for flowering after cold exposure. Hormonal regulation through gibberellins, auxin, and cytokinin signaling pathways modulates floral meristem identity and organ primordia formation. The chapter integrates molecular genetics with physiological responses, demonstrating how environmental cues like temperature and photoperiod are translated into specific gene expression patterns that determine reproductive timing. These mechanisms ensure that flowering occurs under optimal conditions for successful reproduction and seed development.