Biosynthesis of secondary metabolites from phenylalanine. (a) Schematic view of metabolic pathway of 3-deoxyanthocyanidin. Naringenin (center) synthesis from Phe occurs through sequential reactions catalyzed by phenylalanine ammonia lyase (PAL), trans-cinnamate 4-monooxygenase (C4H), 4-coumarate:CoA ligase (4CL), chalcone synthase (CHS), and chalcone isomerase (CHI). 3-deoxyanthocyanidin is synthesized by the action of dihydroflavonol 4-reductase (DFR) and a putative anthocyanidin reductase. Anthocyanidin is synthesized by the actions of flavanone 3-hydroxylases (F3H), and anthocyanindin synthase (ANS) from naringenin. Upregulation of DFR and anthocyanidin reductase genes, and suppression of F3H and ANS genes suggests that 3-deoxyanthocyanidin accumulates but anthocyanin does not. FNSII converts naringenin to flavone through the formation of 2-hydroxyflavanones. (b) Expression of genes associated with secondary metabolism from naringenin. RPKMs for each gene were compared in mock-infected (gray bars) and pathogen-infected (black bars) leaves. An unannotated gene, CUFF115357.1, was upregulated among four DFR genes. A putative anthocyanidin reductase gene (Sb06g029550) was highly upregulated among tandemly duplicated putative paralogs. Expression of an FNSII gene (Sb02g000220.1) was induced among four family members. (c) CUFF115357.1 gene in sorghum and the corresponding region in rice. CUFF115357.1 in sorghum (black) had no corresponding gene in rice. Genes putatively encoded polyubiquitin (UBQ), peroxidase (POD), ROP interacting CRIB motif protein (RIC), amine oxidase (AOX), cytochrome C (CytC), or an unknown protein, or were non-coding transcripts. Corresponding genes are connected by lines. (d) Accumulation of apigeninidin after infection. Pigments extracted from leaf of sorghum BTx623 (control, after infection with Bipolaris sorghicola, or wounding) were subjected to thin layer chromatography. Chemically synthesized apigeninidin was used as a standard.