and Characterization of gene products involved C-glycosyl flavone formation in maize

CASAS, M.I.; MOROHASHI, K; MEJÍA-GUERRA, M.K.; FALCONE FERREYRA, M.L.; RODRIGUEZ, E.; CASATI, P.; GROTEWOLD, E

Oregon

Congreso; 54rd Annual Maize Genetics Conference; 2012

C-glycosyl flavones are specialized compounds that belong to the flavonoid family of specialized compounds and they have been shown to confer natural resistance against corn earworm (Helicoverpa zea), a devastating pest of maize. They accumulate in silks where they exert their biocidal action when ingested by the worm, and to a lesser extent in pericarps, the outermost layer of the maize kernel. This research focuses on the biosynthesis of the C-glycosyl flavone (CGF) maysin, in which the R2R3-MYB transcription factor P1 (or its paralog P2) and the loci salmon silks 1 (SM1), salmon silks 2 (SM2) and recessive enhancer of maysin 1 (REM1) have been proposed to be responsible for the formation and accumulation of CGFs in silks. Salmon silks mutants present a salmon silk phenotype and are positive for the silk browning reaction, which is evident only in the presence of P1 or P2, supporting their involvement in the control of maysin biosynthesis. Even though mutant analyses suggested SM2 has rhamnosyl transferase activity, and that SM1 is involved in the last dehydration step, the identification of the genes responsible for these reactions has yet to be determined. In addition, there has been no activity proposed for REM1 and where it could be placed in the pathway. Starting-off with the hypothesis that P1/P2 regulates these loci, we are searching for candidate genes by analyzing RNA-Seq derived from P1-rr and P1-ww pericarps and silks focusing on genes that are highly expressed in P1-rr tissues in the mapping intervals for each of these loci. Candidate gene analysis and biochemical characterization will help us elucidate the products of the SM1, SM2 and REM1 loci, and expand our knowledge of the branch of the flavonoid pathway that leads to C-glycosyl flavones formation. This Project is funded by NSF DBI-0701405 and IOS-1125620.