Identification and characterization of 1 maize salmon silks genes involved in insecticidal maysin biosynthesis

MA. ISABEL CASAS; MA LORENA FALCONE FERREYRA; NAN JIANG; MARÍA KATHERINE MEJÍA-GUERRA; EDUARDO JOSE RODRIGUEZ; TYLER WILSON; JACOB ENGELMEIER; PAULA CASATI; ERICH GROTEWOLD

PLANT CELL

AMER SOC PLANT BIOLOGISTS

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

1040-4651

The century-old Zea mays (maize) salmon silks mutation has been linked to theabsence of maysin. Maysin is a C-glycosyl flavone that, when present in silks, confersnatural resistance to the corn earworm (Helicoverpa zea), which is one of the mostdamaging pests of maize in America. Previous genetic analyses predicted PericarpColor1 (P1, R2R3-MYB transcription factor) to be epistatic to the sm mutation.Subsequent studies identified two loci as being capable of conferring salmon silksphenotypes, salmon silks 1 (sm1) and salmon silks 2 (sm2). Benefitting from availablesm1 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. Sm2encodes a rhamnosyl transferase (UGT91L1) that uses isoorientin and UDP-rhamnoseas substrates, and converts them to rhamnosylisoorientin. Sm1 encodes a multidomainUDP-rhamnose synthase (RHS1) that converts UDP-glucose into UDP-L-rhamnose.Here, we demonstrate that RHS1 shows unexpected substrate plasticity in convertingthe glucose moiety in rhamnosylisoorientin to 4-keto-6-deoxy glucose, resulting inmaysin. Both Sm1 and Sm2 are direct targets of P1, as demonstrated by chromatinimmunoprecipitation (ChIP) experiments. The molecular characterization of Sm1 andSm2 described here completes the maysin biosynthetic pathway, providing powerfultools for engineering tolerance to corn earworm in maize and other plants.