The process begins with heat-damaged hardened nucleolus, from which a nucleolar seedling grows. A red horizontal line with a red vertical line at the tip is labeled arrest, and it points to the step 1: heat-damaged hardened nucleolus. In the next step, bud enlargement through de novo synthesis occurs, which is followed by partial nuclear envelope breakdown. The next step is chaperone-mediated partitioning of old nucleolus, from which an arrow labeled regrowth points to another arrow labeled time after heat stress; the arrow labeled time after heat stress points downward from step 1 to step 6. The final step is the disassembly and preferential segregation of new nucleolus, with the extrusion and clearance of old nucleolus and daughter nucleus labeled. A key at the top indicates N o p 1 (old slash new) by magenta color, H s p 104 by green, chromatin by gray, and nuclear envelope by blue.
Model for nucleolar remodeling, partitioning, and quality control following heat shock. Schematic illustration of nucleolar remodeling in M. oryzae during recovery from heat stress. (1) Heat shock damages the existing nucleolus. (2–3) A new nucleolar bud emerges from the old (preexisting) nucleolus and expands through de novo synthesis. (4) Partial nuclear envelope breakdown permits entry of the molecular chaperones such as Hsp104 and Hsp70. (5) The old nucleolar compartment accumulates SUMO-modified material and selectively recruits Hsp70 and Hsp104, mediating the partitioning of old and new nucleolar material. (6) The newly formed nucleolus disassembles at mitotic onset and is preferentially inherited by daughter nuclei, while the old nucleolus is extruded and diminishes.