Acyl-CoA-binding protein families in the plant kingdom

Abstract

Acyl-CoA-binding proteins (ACBPs), ubiquitous in eukaryotes, participate in lipid metabolism by binding acyl-CoA esters at the conserved acyl-CoA-binding (ACB) domain. Phylogenetic analyses on 16 plant genomes comprising green alga, mosses, gymnosperm, monocots and dicots revealed that the ACBP family expanded with the evolution of land plants. The plant ACBP family is clustered into four groups, designated as Class I to Class IV. Class I is identical to the prototype ACBP protein (10-kDa) that has been well-studied in mammals and yeast. Class II and Class IV proteins consist of an ACB domain as well as ankyrin repeats or kelch motifs, respectively. Class III proteins form larger proteins that contain an ACB domain. Classes I and IV seemed to have evolved independently, while Classes II and III are closely related phylogenetically. The ACBP family in the eudicot model plant, Arabidopsis, has six members that have been previously characterized. The ACBP family in the monocot, rice, also consists of six members but their distribution across the four classes differ from Arabidopsis. There are three Class I members in rice, while only one occurs in Arabidopsis. Furthermore, two each of Class II and Class IV have been identified in Arabidopsis while one each exists in rice. However, only one Class III member is present in both Arabidopsis and rice. Results from our investigations suggest that rice ACBPs have non-overlapping functions and the larger and multi-domain forms appear to be related to stress responses.