Isolation and characterization of germacrene A synthases gene in Citrus unshiu Marc

CuSTS1 cDNA clone was isolated from Satsuma mandarin (Citrus unshiu Marc.) and functionally characterized. Genomic clone corresponding to CuSTS1 consists of 7 exons and 6 introns which is typical structure of angiosperm sesquiterpene synthase genes. Their predicted proteins possess a general feature of plant sesquiterpene synthases and RR motif and DDXXD motifs were conserved. Phylogenetic tree analysis showed that the molecular evolutions of citrus germacrene synthase might occur according to enzymatic function before the divergence of Citrus species, in contrast to citrus monoterpene synthase genes. Functionally analysis indicated that CuSTS1 protein produces mainly germacrene A from farnesyl diphosphate (FPP) in accompany with side product.In Satsuma mandarin, transcription of CuSTS1 were comparatively abundant in flowers and young fruit at 60 days after flowering (DAF), and peel at 120 DAF. The transcription was decreasing toward fruit maturing. In young fruit at 120 DAF, CuSTS1 is induced by methyl jasmonic acid, salicylic acid and ethylene treatments, suggesting it would be involved in plant defense response.

► This manuscript is firstly characterized for germacrene A synthase gene in Citrus species.
► The gene identification of mono- or sesqui-terpene could not be estimated from nucleotide sequence and enzymatic characterization is indispensable.
► The information of transcriptional data and gene function is valuable to consider bio-function role of sesquiterpenes in citrus species.
► Besides, it was found that the molecular evolutions of citrus germacrene synthase might occur according to enzymatic function before the divergence of Citrus species, in contrast to citrus monoterpene synthase genes (which occur after the divergence of Citrus species).