Changes Of The Content Of Volatile Terpenoids Under UV-B Irradiation And Identification Of Related Terpene Synthases In Rice Leaves

Terpenoids are the most abundant secondary metabolites in nature.They are widespread in higher plants,microorganisms,insects,and marine organisms.Terpenoids have an important role in organisms.They are involved in the defense responses to various stress(such as insect pests,etc.),and they also serve as advertisements to attract pollinators and dispersal agents in plants.Abundant terpenoids in nature are also great repositories for human industrial production and drug research.Some terpenoids are important industrial raw materials,and some are used as medicines to prevent and treat various diseases.The research on terpenoids has always been the hot spot of life science research.At present,the functions and related synthesis pathways of terpenoids in plants are mainly studied.Many studies have shown that terpenoids play an important role in direct and indirect defense of plants.In recent years,the functions of terpenoids have been reported in many biological stresses,and their functional studies under abiotic stress have also been paid attention to by scholars.With the destruction of the Earth's ozone layer,ultraviolet(UV)irradiation as a non-biological stress on the physiological and ecological research of plants has attracted more and more attention from researchers.Rice is an important crop,and its yield and quality have always been the focus of crop research.Since the yield and quality of rice are often affected by the environment,terpeniods as active substances anti adversity in plants,so it is of great significance to study the function of terpenoids in rice under UV-B stress.In this study,we first detected and identified eight volatile terpenoids in rice leaves by chromatography-mass spectrometry(GC-MS),in which monoterpenoids are alpha-pinene,beta-myrcene,limonene,ocimene,linalool,geraniol,and sesquiterpene compounds are trans-nerolidol and trans-farnesol.Quantitative analysis of these eight volatile terpenoids in rice leaves revealed that sesquiterpene trans-farnesol is the major component of these eight volatile terpenoids in rice leaves(74.93%).However,the content of geraniol and trans-farnesol in rice leaf was significantly increased when rice seedlings at the tree-leaf stage induced by UV-B.Because terpene synthase is a key enzyme in the synthetic pathway of terpenoids,and its expression level has an important effect on the content of terpenoids in plants.By detecting the transcriptional level of rice terpene synthase(OsTPS)using real-time RT-PCR,we found three OsTPSs with significantly increased expression after UV-B induction,which were OsTPSl,OsTPS28,and OsTPS30,respectively.Subcellular localization experiments showed that all these three enzymes were located in the cytoplasm.Prokaryotic expression and purification of the three enzymes were performed and then tested their enzyme activities in vitro.OsTPS1 was found to encode a sesquiterpene synthase producing trans-nerolidol and trans-farnesol.OsTPS28 was found to encode a sesquiterpene synthase producing the single product trans-nerolidol,and OsTPS30 was found to encode a monoterpene synthase producing the single product geraniol or a sesquiterpene synthase producing the single product trans-farnesol,which is the most abundant volatile terpene from rice leaves and accumulated after UV-B induction.Phylogenetic analysis of these three enzymes showed that all these three enzymes belong to the TPS-a class protein.These results indicate that OsTPS1 and OsTPS30 genes could be induced in rice after exposure to UV-B irradiation,thus accumulating more trans-farnesol in rice to participate in defense response to UV-B stress of rice leaves.