The known cues for switching from vegetative to reproductive stage in flowering plants are daylight time and temperature increase. However, the molecular mechanisms underlying this switch are far from being obvious. A novel study reveals that day length increase triggers a molecular signaling cascade, resulting in chromatin remodeling within the cell.

Long strands of DNA within the nucleus associate with protein building blocks, called histones, to form highly ordered chromatin. This packaging ensures stable organization of this delicate molecule, as well as provides certain transcriptional control. The actively transcribed regions of DNA are packed relatively loosely (euchromatin), while the tightly packaged fragments of chromatin (heterochromatin) receive little to none transcriptional activity.

It should be noted that cell can regulate the shift from euchromatic to heterochromatin (or vice versa) in response to certain conditions. One of the main mechanisms for this packaging/unpackaging is acetylation and deacetylation of DNA. The scientists show that acetylation and deacetylation cycles is the main mechanism for fine-tuning flowering time in “long day” flowering plants.

After a long day of sunlight, a “flowering signal”, commonly known as florigen, is produced in the leaves, and travels throughout the plant to facilitate formation of flower buds. The researchers now uncover that florigen upregulation is mostly dependent on the acetylation of DNA, which “unravels” chromatin to expose flowering protein genes. Even more importantly, a strict control of the process is implemented by the reverse process of deacetylation – histone deacetylases are activated specifically at dusk, thus diming the “flowering-on” signal induced by florigen. This way plants are prevented from flowering too soon, since premature blossoms have little chance to be pollinated too early in the spring.

Finding the best time to blossom is of vital importance for plants, however interpreting complex environmental cues is a considerable task. Discovering the molecular components of an efficient DNA packaging and repackaging system adds an important piece to the puzzle of the ever-elusive life of flowering plants.

Source: www.technology.org