Characterization And Analysis Of Metabolic Gene Clusters For Specialized Metabolites Biosynthesis In Tobacco

Nicotiana tabacum L.(common tobacco)has attracted much interest as one of the most economically important industrial crops.Common tobacco is abundant with bioactive natural products or specialized metabolites,which contribute a lot to defense against herbivores and microbial pathogens,especially terpenoid phytoalexins.And this makes tobacco itself to be a frequently investigated ecological role of their specialized metabolites in responses to biotic stress factors.Metabolic gene cluster in plants is defined as a set of two or more non-homologous genes encoding enzymes from the same biosynthesis pathway.Genes encoding these enzymes arranged in this kind of co-occurrence pattern greatly contribute to rapid stress response,gene coregulation,co-function and co-heredity,in a manner like the operon in prokaryotic genomes.Genome-wide identification of the functional metabolic gene clusters in tobacco will dramatically improve the efficiency of genome editing for improving economical traits.Though in silico approaches for genome-wide gene clusters' prediction have been developed well,a comprehensive pipeline which integrated the co-expression analysis with metabolic pathway annotation for screening genuine metabolic gene clusters is still absent.In this study,the cultivar K326 of common tobacco was taken for investigation,and we performed a genome? wide prediction and intensive analysis of metabolic gene clusters.We got the following results:(1)Our analyses shed light on metabolic gene clusters' detection in common tobacco with a complex genome,where customized and modified analyses are required.The pipeline raised here could also be used in other plants with complex genomes.(2)We predicted 1,181 metabolic gene clusters with 34 of them potentially being involved in terpenoid biosynthesis.Through integration with transcriptome and metabolic pathway annotation analyses,3 of the 34 terpenoid biosynthesis-related gene clusters were determined to be high-confidence ones,with 2 involved in biosynthesis of capsidiol,a terpenoid recognized as one of the effective resistance compounds in the Nicotiana species.(3)In this study,the well-known phytotoxin capsidiol in tobacco was found to be functioning in a clustering pattern.The capsidiol biosynthesis gene cluster was conserved in N.sylvestris,N.tomentosiformis and N.attenuate,and other two cultivars of common tobacco(TN90 and BX),which highlights the significance of capsidiol in the evolution of the Nicotiana species.