Identification and characterization of maize salmon silks genes involved in insecticidal maysin biosynthesis

JIAN, N; WILSON, T; GROTEWOLD, E.; FALCONE FERREYRA, M.L.; RODRIGUEZ, E.; CASATI, P.; CASAS, M.I; MEJÍA-GUERRA, M.K.; ENGELMEIER, J

PLANT CELL

AMER SOC PLANT BIOLOGISTS

Lugar: Rockville; Año: 2016 vol. 28 p. 1297 - 1309

1040-4651

The century-old Zea mays (maize) salmon silks mutation has been linked to the absence of maysin. Maysin is a C-glycosyl flavone that, when present in silks, confers natural resistance to the corn earworm (Helicoverpa zea), which is one of the most damaging pests of maize in America. Previous genetic analyses predicted Pericarp Color1 (P1, R2R3-MYB transcription factor) to be epistatic to the sm mutation. Subsequent studies identified two loci as being capable of conferring salmon silks phenotypes, salmon silks 1 (sm1) and salmon silks 2 (sm2). Benefitting from available sm1 and sm2 mapping information and from knowledge of the genes regulated by P1, we describe here the molecular identification of the Sm1 and Sm2 gene products. Sm2 encodes a rhamnosyl transferase (UGT91L1) that uses isoorientin and UDP-rhamnose as substrates, and converts them to rhamnosylisoorientin. Sm1 encodes a multidomain UDP-rhamnose synthase (RHS1) that converts UDP-glucose into UDP-L-rhamnose. Here, we demonstrate that RHS1 shows unexpected substrate plasticity in converting the glucose moiety in rhamnosylisoorientin to 4-keto-6-deoxy glucose, resulting in maysin. Both Sm1 and Sm2 are direct targets of P1, as demonstrated by chromatin immunoprecipitation (ChIP) experiments. The molecular characterization of Sm1 and Sm2 described here completes the maysin biosynthetic pathway, providing powerful tools for engineering tolerance to corn earworm in maize and other plants.