Plant signaling systems. Plastid-generated signals and their role in nuclear gene expression

Current concepts are outlined regarding the chloroplast effects on expression of the nuclear genes encoding plastid proteins. The major types of plastid-generated signals are considered. The signal molecules are shown to include the reactive oxygen species, the redox state of the components of photosynthetic electron transport, in particular plastoquinones, the redox-active molecules of plastid stroma, such as thioredoxin and glutathione, and also the intermediates of tetrapyrrole biosynthesis (Mg-protoporphyrin IX and its monomethyl ester). The sophisticated regulatory network is emphasized as a channel matching up the expression of nuclear and plastid genes. The plastid-generated signals help plants adapt to the changing and frequently adverse environmental conditions.