Figure 3.

Mechanisms and main players involved in the maintenance of plastid proteostasis, which affects foreign protein accumulation. Transcriptional and translational control, proteases, molecular chaperones, protein folding, and targeting are graphically illustrated. For discussion, see text. The yellow squares with a red C inside indicate chaperone pathways; the yellow squares with a red P inside indicate proteases. The yellow triangle with black PR inside indicates the transgene promoter. 5′-UTRs and 3′-UTRs are indicated, as well as the AUG translation initiation codon and the sequences downstream of it that affect transcript stability and/or translation (downstream box region [DB]). RBPs, RNA-binding proteins.