Functional analysis of paralogous genes in acetyl coenzyme A metabolism

Abstract

Acetyl-CoA is responsible for much of the structural and functional diversity in nature, as it provides organisms with the chemical flexibility to biosynthesize a plethora of natural products. Recent studies in Arabidopsis using antisense RNA technology have demonstrated that an overall reduction of ATP-citrate lyase (ACL) activity in the cytosol produces a complex morphological and biochemical phenotype. Significant complementation of the phenotype with malonic acid demonstrated that the observed metabolic alterations were related to the carboxylation pathway of cytosolic acetyl-CoA metabolism. However, Arabidopsis ACL is encoded by two small subfamilies of highly homologous genes. In Arabidopsis, functional ACL is an A4B4 heterooctamer, and the ACLA subunit is encoded by three genes while the ACLB subunit is encoded by two. The individual physiological roles of each of these genes have not been determined. In this study we report the isolation of TDNA of Ds transposon insertion mutants for each gene in the ACL family. By intercrossing aclb1 and aclb2 mutants, we have shown that the ACL null condition is embryo lethal. This finding demonstrates that normal growth and development requires an adequate ACLgenerated cytosolic acetyl-CoA pool which cannot be complemented by any other endogenous source of acetyl-CoA. We have also demonstrated that, in spite of the different expression patterns observed, ACLA genes display substantial functional redundancy, as genetic disruption of these, individually or in pair, produces no morphological and few biochemical phenotypes.