Independent evolution of the prochlorophyte and green plant chlorophyll a/b light-harvesting proteins

The prochlorophytes are oxygenic prokaryotes differing from other cyanobacteria by the presence of a light-harvesting system containing both chlorophylls (Chls) a and b and by the absence of phycobilins. We demonstrate here that the Chl a/b binding proteins from all three known prochlorophyte genera are closely related to IsiA, a cyanobacterial Chl a-binding protein induced by iron starvation, and to CP43, a constitutively expressed Chl a antenna protein of photosystem II. The prochlorophyte Chl a/b protein (pcb) genes do not belong to the extended gene family encoding eukaryotic Chl a/b and Chl a/c light-harvesting proteins. Although higher plants and prochlorophytes share common pigment complements, their light-harvesting systems have evolved independently.

原绿藻（prochlorophytes）是一类产氧原核生物，与其他蓝细菌（cyanobacteria）的差异在于其捕光系统同时包含叶绿素a与叶绿素b（Chls a、b），且不含藻胆素（phycobilins）。本研究证实，目前已知的三个原绿藻属的叶绿素a/b结合蛋白，均与铁饥饿诱导的蓝细菌叶绿素a结合蛋白IsiA，以及光系统II组成型表达的叶绿素a天线蛋白CP43具有高度同源性。原绿藻的叶绿素a/b结合蛋白编码基因（pcb基因）并不属于编码真核生物叶绿素a/b及叶绿素a/c捕光蛋白的扩展基因家族。尽管高等植物与原绿藻拥有一致的色素组成，二者的捕光系统却经历了独立演化。