Table 1.

Source of typical retrograde signals in plants.

Group	Typical Member	References
β-Carotene	β-cyclocitral	[43]
ROS	1O2	[50]
	H2O2	[44]
Tetrapyrrole	Mg-ProtoIX	[51]
	heme	[48]
Sulfation	PAP	[25]
Kinases	MAPK6	[47]
Methylerythritol isoprenoid	MEcPP	[23]
Transcription factors	AP2	[49]
	Whirly1	[52]
Chloroplast envelop proteins	PTM/PHD	[53]