Annett Richter, Claudia Schaff, Zhiwu Zhang, Alexander E. Lipka, Feng Tian, Tobias G. Köllnerc, Christiane Schneec, Susanne Preißa, Sandra Irmischc, Georg Jander, Willhelm Boland, Jonathan Gershenzon, Edward S. Buckler, and Jörg Degenhardt

The Plant Cell September 23, 2016 tpc.00919.2015

ABSTRACT

Plant volatiles not only have multiple defense functions against herbivores, fungi, and bacteria, but also have 33 been implicated in signaling within the plant and towards other organisms. Elucidating the function of individual 34 plant volatiles will require more knowledge of their biosynthesis and regulation in response to external stimuli. 35 By exploiting the variation of herbivore-induced volatiles among 26 maize (Zea mays) inbred lines, we 36 conducted a nested association mapping (NAM) and genome-wide association study (GWAS) to identify a set 37 of quantitative trait loci (QTLs) for investigating the pathways of volatile terpene production. The most 38 significant identified QTL affects the emission of (E)-nerolidol, linalool, and the two homoterpenes, 3,8-39 dimethyl-1,4,7-nonatriene (DMNT), and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT). GWAS 40 associated a single nucleotide polymorphism in the promoter of the gene encoding the terpene synthase TPS2 41 with this QTL. Biochemical characterization of TPS2 verified that this plastid-localized enzyme forms linalool, 42 (E)-nerolidol, and (E,E)-geranyllinalool. The subsequent conversion of (E)-nerolidol into DMNT maps to a P450 43 monooxygenase, CYP92C5, which is capable of converting nerolidol into DMNT by oxidative degradation. A 44 QTL influencing TMTT accumulation corresponds to a similar monooxygenase, CYP92C6, which is specific for 45 the conversion of (E,E)-geranyllinalool to TMTT. The DMNT biosynthetic pathway and both monooxygenases are distinct from those previously characterized for DMNT and TMTT synthesis in Arabidopsis, suggesting 47 independent evolution of these enzymatic activities. 

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Figure 3. Mapping of QTL606 for Nerolidol Production by Genome Wide Association Study (GWAS) Using 1.6 million SNP Markers.  (A) The bar graph presents the counts of iterations by GWAS for each of the SNPs located near QTL606. The counts of iterations are shown above the most prominent bars. The SNP with the most significant correlation to QTL606 (indicated by a black bar) is positioned in the promoter region of tps2 (arrow). Shown above is the pattern of exons (boxes) and introns (lines) of tps2 with the number of nucleotides from the translation start. (B) Location of tps2, tps3, and the most relevant QTLs in a section of chromosome 5 (wide grey line). A closeup of this region (thin grey line) shows the positon of SNP 70571650 in relation to tps2 and tps3. For both tps2 and tps3, the respective pattern of exons (black boxes) and introns (black lines) are pictured below.