Maize (Zea mays) is a major staple crop in Africa, where its yield and the livelihood of millions are compromised by the parasitic witchweed Striga. Germination of Striga is induced by strigolactones exuded from maize roots into the rhizosphere. In a maize germplasm collection, we identified two strigolactones, zealactol and zealactonoic acid, which stimulate less Striga germination than the major maize strigolactone, zealactone. We then showed that a single cytochrome P450, ZmCYP706C37, catalyzes a series of oxidative steps in the maize-strigolactone biosynthetic pathway. Reduction in activity of this enzyme and two others involved in the pathway, ZmMAX1b and ZmCLAMT1, can change strigolactone composition and reduce Striga germination and infection. These results offer prospects for breeding Striga-resistant maize.

Bioinformatics Group Wageningen University and Research 6708 PB Wageningen Netherlands

Department of Economic Plants and Biotechnology Yunnan Key Laboratory for Wild Plant Resources Kunming Institute of Botany Chinese Academy of Sciences Kunming 650201 China

Horticultural Sciences Department University of Florida Gainesville FL 32611 USA

International Institute of Tropical Agriculture PMB 5320 Oyo Road Ibadan Nigeria

International Maize and Wheat Improvement Center PO Box 1041 00621 Nairobi Kenya

Kyoto University iCeMS Yoshida Ushinomiya cho Sakyo ku Kyoto 606 8501 Japan

Laboratorium für Organische Chemie Department of Chemistry and Applied Biosciences ETH Zürich 8093 Zürich Switzerland

Laboratory of Growth Regulators Institute of Experimental Botany The Czech Academy of Sciences and Faculty of Science Palacký University Šlechtitelů 27 783 71 Olomouc Czech Republic

Plant genomics and transcriptomics group Institute of Biosciences Sao Paulo State University 13506 900 Rio Claro Brazil

Plant Hormone Biology Group Swammerdam Institute for Life Sciences University of Amsterdam Science Park 904 1098 XH Amsterdam Netherlands

Section of Cell and Developmental Biology University of California at San Diego; La Jolla CA 92093 USA

Seeds Research Syngenta Crop Protection LLC Research Triangle Park NC 27709 USA

Syngenta Crop Protection AG Schaffhauserstrasse 101 CH 4332 Stein Switzerland

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