Melatonin in the evolution of plants and other phototrophs

Abstract

Melatonin
 is present in numerous phototrophic eukaryotes, not only in plants in the
 meaning of Archaeplastida or of Viridiplantae. It is also formed in members of
 other superclades, such as Excavata and SAR clade. Typically, their respective
 phototrophs have acquired chloroplasts from phototrophic eukaryotes, either by
 taking them up as endosymbionts or by chloroplast capturing. It has been the
 aim of this overview to trace the phylogenetic relationships between the
 various phototrophs according to actual, genetically based taxonomy. This
 includes the consideration of primary heterotrophs that also exist within the
 same groups and some secondary heterotrophs that have lost functional
 chloroplasts. The presence of melatonin in these different taxa is discussed
 under the aspects of its cyanobacterial or α-proteobacterial origins, as
 transmitted by plastidial or mitochondrial ancestors, or by horizontal gene
 transfer. Peculiarities of melatonin metabolism that have evolved in some of
 these groups are also addressed.