Figure 2.

Light-dependent nuclear organization dynamics in cotyledons. During the first 2 days of germination, seed imbibition initiates nuclear expansion and heterochromatin decondensation, as shown by the dispersed signal of methylated DNA immunolabeling in both dark and light conditions (Phase 1). From the third day of germination, light perception triggers further nuclear expansion and the re-compaction of pericentromeric domains within cytologically observable chromocenters (Phase 2), whereas in the absence of light, heterochromatin is further decondensed (Phase 3). Skotomorphogenic nuclear phenotypes can rapidly be converted to a photomorphogenic-type organization during cotyledon de-etiolation (Phase 4). Cotyledon de-etiolation also involves the relocation of light-inducible genes to the nuclear periphery (such as the CAB locus), and the aggregation of photoreceptors and downstream signaling components, such as phyB, COP1, PIFs, and TZP into sub-nuclear speckles referred to as photobodies. d; days post-imbibition.