Multifunctional 5-hydroxyconiferaldehyde O-methyltransferases (CAldOMTs) in plant metabolism

Lignin, flavonoids, melatonin, and stilbenes are plant specialized metabolites with diverse physiological and biological functions, supporting plant growth and conferring stress resistance. Their biosynthesis requires O-methylations catalyzed by 5-hydroxyconiferaldehyde O-methyltransferase (CAldOMT; also called caffeic acid O-methyltransferase, COMT). CAldOMT was first known for its roles in syringyl (S) lignin biosynthesis in angiosperm cell walls and later found to be multifunctional. This enzyme also catalyzes O-methylations in flavonoid, melatonin, and stilbene biosynthetic pathways. Phylogenetic analysis indicated the convergent evolution of enzymes with OMT activities towards the monolignol biosynthetic pathway intermediates in some gymnosperm species that lack S-lignin and Selaginella moellendorffii, a lycophyte which produces S-lignin. Furthermore, neofunctionalization of CAldOMTs occurred repeatedly during evolution, generating unique O-methyltransferases (OMTs) with novel catalytic activities and/or accepting novel substrates, including lignans, 1,2,3-trihydroxybenzene, and phenylpropenes. This review summarizes multiple aspects of CAldOMTs and their related proteins in plant metabolism and discusses their evolution, molecular mechanism, and roles in biorefineries, agriculture, and synthetic biology.

RNAi-Based Gene Silencing in Sugarcane for Production of Biofuel

RNA interference (RNAi) is an innate cellular mechanism triggered by a double-stranded RNA (dsRNA) molecule causing selective inhibition of gene expression. Here, we demonstrated the RNAi technology for gene silencing in sugarcane for biofuel production. This chapter describes an efficient model system that established to target the caffeic acid O-methyltransferase (COMT) gene and the RNAi construct is designed and delivered through Agrobacterium mediated stable sugarcane transformation. Also, the approach for an analysis of resulting putative transgenic plants for a targeted RNAi mediated gene silencing is described.