Citrus CmTPS1 is associated with formation of sesquiterpene bicyclogermacrene

Citrus are rich in volatile terpenoids related to fruit flavor and defence response. Remarkable differences in Citrus volatiles provide us an ideal plant material to characterize novel genes associated with volatile formation. Bicyclogermacrene, a sesquiterpene, has high free radical scavenging activity and accumulates in finger citron (Citrus medico L. var. Sarcodactylis Hort) that belongs to wild species of Citrus family. In the present study, CmTPS1 comprised of 1668 base pairs was cloned, belonging to TPS-a subfamily. Transiently transform in tobacco leaf cells showed that CmTPS1 protein localized in the cytoplast. Enzyme activity assay showed that recombinant CmTPS1 catalyzed in vitro formation of bicyclogermacrene toward farnesyl diphosphate (FPP) as the substrates. Homologous transient over-expression in finger citron indicated that CmTPS1 also contributed to in vivo biosynthesis of bicyclogermacrene. Accumulated concentration of bicyclogermacrene positively correlated with CmTPS1 transcripts in developing fruit, flowers and leaves of finger citron. Melatonin treatment increased bicyclogermacrene contnent and CmTPS1 transcripts levels. Bicyclogermacrene was detected in finger citron fruit, but was under detected limits in mandarin, sweet orange and Citrus hybrids. Similar profile was observed for transcript levels of GnTPS1. These results indicated that CritTPS1 was associated with formation of sesquiterpene bicyclogermacrene in Citrus.