Cloning and characterisation of two genes for 3-hydroxy-3-methylglutaryl coenzyme A reductase and their possible roles during fruit development in Dimocarpus longan

Abstract

Summary3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR; EC: 1.1.1.34), encoded by multiple genes in eukaryotes, is known to catalyse the first committed step in the mevalonic acid (MVA) pathway for the biosynthesis of isoprenoids, and has been implicated in fruit size determination. To elucidate whether the genes for HMGR are involved in the regulation of fruit growth in longan (Dimocarpus longan), we cloned two sequence-distinct HMGR genes, designated DlHMG1 and DlHMG2, respectively. Sequence analyses revealed that they shared a high level of sequence and domain conservation, with homologues identified in other species at both the nucleotide and amino acid levels. Gene expression analysis showed that the two genes were differentially regulated in the pericarp, arils, and seed, as well as during fruit development. DlHMG1 was up-regulated particularly in Phase I [0 – 42 d after anthesis (DAA)] and at the early stage of Phase II (42 – 56 DAA), followed by down-regulation in Phase III (≥ 56 DAA); while DlHMG2 was expressed constitutively in the pericarp and arils, but fluctuated periodically in seed tissues during fruit development. The possible roles of DlHMG1 and DlHMG2 in the regulation of longan fruit size and growth are discussed.