Figure 8.

Impaired Plastid Division Triggers Cell Cycle Inhibition and Cell Death.

(A) Under nonstress conditions, plastid division precedes cell division, enabling equal partitioning of plastids into the daughter cells.

(B) In GC mutants, impaired plastid division seems to repress the cell cycle via cell cycle inhibitors such as SMR5 and SMR7 (Hudik et al., 2014). Whereas the role of SMR5 in crl mutant was previously demonstrated and shown to be partly responsible for the cell cycle inhibition, the impact of SMR7 induction remains unclear. Besides, GCs are largely defective in ROS and lipid homeostasis, leading to an increase in lipid peroxidation (LPO) and perhaps also RES. The abrogated and attenuated cell death caused by the loss of FAD5 in crl and other GC mutants, respectively, indicates the pivotal roles of LPO and RES in developing the multiple lesions. At present, it remains unknown whether any natural stress results in an arrest in plastid division, which leads to cell cycle arrest and controlled cell death.