|HANDRICK, VINZENZ - Max Planck Institute Of Molecular Plant Physiology|
|ROBERT, CHRISTELLE - University Of Bern|
|AHEM, KEVIN - Boyce Thompson Institute|
|ZHOU, SHAOQUN - Boyce Thompson Institute|
|MACHADO, RICHARDO - University Of Bern|
|MAAG, DANIEL - University Of Neuchatel|
|GLAUSER, GAETAN - University Of Neuchatel|
|FERNANDEZ-PENNY, FELIX - Boyce Thompson Institute|
|CHANDRAN, JIMA - Max Planck Institute Of Molecular Plant Physiology|
|RODGERS-MELNICK, ELI - Cornell University|
|SCHNEIDER, BERND - Max Planck Institute Of Molecular Plant Physiology|
|Buckler, Edward - Ed|
|BOLAND, WILHELM - Max Planck Institute Of Molecular Plant Physiology|
|GERSHENZON, JONATHAN - Max Planck Institute Of Molecular Plant Physiology|
|JANDER, GEORG - Boyce Thompson Institute|
|ERB, MATTHIAS - University Of Bern|
|KOLLNER, TOBIAS - Max Planck Institute Of Molecular Plant Physiology|
Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2016
Publication Date: 6/17/2016
Citation: Handrick, V., Robert, C., Ahem, K., Zhou, S., Machado, R., Maag, D., Glauser, G., Fernandez-Penny, F., Chandran, J., Rodgers-Melnick, E., Schneider, B., Buckler IV, E.S., Boland, W., Gershenzon, J., Jander, G., Erb, M., Kollner, T. 2016. Biosynthesis of 8-O-methylated benzoxazinoid defense compounds in maize. The Plant Cell. 28(7):1682-1700.
Interpretive Summary: Plants produce a wide range of chemical compounds to naturally fight off insects. However, the scientific problem is that insect pressures are rapidly changing, and so crops need to constantly match their defensive chemicals to the current threats. In this study, using advanced genomics combined with a survey of maize natural variation, a genome-wide quantitative trait mapping strategy revealed a side branch of the benzoxazinoid pathway that specifically increases maize resistance against aphids. The gene and variants that were identified can now be used to provide specific protection against phloem (sap) feeding insects. This knowledge can be rapidly deployed across breeding programs.
Technical Abstract: Benzoxazinoids are important defense compounds in grasses. Here, we investigated the biosynthesis and biological roles of the 8-O-methylated benzoxazinoids, DIM2BOA-Glc and HDM2BOA-Glc. Using quantitative trait locus mapping and heterologous expression, we identified a 2-oxoglutarate-dependent dioxygenase (BX13) that catalyzes the conversion of DIMBOA-Glc into a new benzoxazinoid intermediate (TRIMBOA-Glc) by an uncommon reaction involving a hydroxylation and a likely ortho-rearrangement of a methoxy group. TRIMBOA-Glc is then converted to DIM2BOA-Glc by a previously described O-methyltransferase BX7. Furthermore, we identified an O-methyltransferase (BX14) that converts DIM2BOA-Glc to HDM2BOA-Glc. The role of these enzymes in vivo was demonstrated by characterizing recombinant inbred lines, including Oh43, which has a point mutation in the start codon of Bx13 and lacks both DIM2BOA-Glc and HDM2BOA-Glc, and Il14H, which has an inactive Bx14 allele and lacks HDM2BOA-Glc in leaves. Experiments with near-isogenic maize lines derived from crosses between B73 and Oh43 revealed that the absence of DIM2BOA-Glc and HDM2BOA-Glc does not alter the constitutive accumulation or deglucosylation of other benzoxazinoids. The growth of various chewing herbivores was not significantly affected by the absence of BX13-dependent metabolites, while aphid performance increased, suggesting that DIM2BOA-Glc and/or HDM2BOA-Glc provide specific protection against phloem feeding insects.