Seeing new light: recent insights into the occurrence and regulation of chromatic acclimation in cyanobacteria

• Chromatic acclimation (CA) tunes physiology, including pigmentation, to light cues.
• CA first described three types of acclimation of PE and/or PC to red or green light.
• Recognized forms of CA in cyanobacteria have expanded to include five types.
• Wavelengths of light responsible for CA in cyanobacteria now span blue into far-red.
• Photoreceptors control transcriptional and post-transcriptional processes during CA.

Cyanobacteria exhibit a form of photomorphogenesis termed chromatic acclimation (CA), which involves tuning metabolism and physiology to external light cues, with the most readily recognized acclimation being the alteration of pigmentation. Historically, CA has been represented by three types that occur in organisms which synthesize green-light-absorbing phycoerythrin (PE) and red-light-absorbing phycocyanin (PC). The distinct CA types depend upon whether organisms adjust levels of PE (type II), both PE and PC (type III, also complementary chromatic acclimation), or neither (type I) in response to red or green wavelengths. Recently new forms of CA have been described which include responses to blue and green light (type IV) or far-red light (FaRLiP). Here, the molecular bases of distinct forms of CA are discussed.