Data from: Genetic mapping shows intraspecific variation and transgressive segregation for caterpillar-induced aphid resistance in maize

Plants in nature have inducible defenses that sometimes lead to targeted resistance against particular herbivores, but susceptibility to others. The metabolic diversity and genetic resources available for maize (Zea mays) make this a suitable system for a mechanistic study of within-species variation in such plant-mediated interactions between herbivores. Beet armyworms (Spodoptera exigua) and corn leaf aphids (Rhopalosiphum maidis) are two naturally occurring maize herbivores with different feeding habits. Whereas chewing herbivore-induced methylation of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside (DIMBOA-Glc) to form 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside (HDMBOA-Glc) promotes caterpillar resistance, lower DIMBOA-Glc levels favor aphid reproduction. Thus, caterpillar-induced DIMBOA-Glc methyltransferase activity in maize is predicted to promote aphid growth. To test this hypothesis, the impact of S. exigua feeding on R. maidis progeny production was assessed using seventeen genetically diverse maize inbred lines. Whereas aphid progeny production was increased by prior caterpillar feeding on lines B73, Ki11, Ki3, and Tx303, it decreased on lines Ky21, CML103, Mo18W, and W22. Genetic mapping of this trait in a population of B73 x Ky21 recombinant inbred lines identified significant quantitative trait loci on maize chromosomes 1, 7 and 10. There is transgressive segregation for aphid resistance, with the Ky21 alleles on chromosomes 1 and 7 and the B73 allele on chromosome 10 increasing aphid progeny production. The chromosome 1 QTL coincides with a cluster of three maize genes encoding benzoxazinoid O-methyltransferases that convert DIMBOA-Glc to HDMBOA-Glc. Gene expression studies and benzoxazinoid measurements indicate that S. exigua-induced responses in this pathway differentially affect R. maidis resistance in B73 and Ky21.

自然界中的植物具备诱导防御（inducible defenses）机制，有时可对特定植食性昆虫产生靶向抗性，却对其他类群易感。玉米（Zea mays）所拥有的代谢多样性与遗传资源，使其成为研究植食者间这类植物介导的种内互作变异机制的理想实验体系。甜菜夜蛾（Spodoptera exigua）与玉米叶蚜（Rhopalosiphum maidis）是两种取食习性迥异的天然玉米植食性昆虫。咀嚼式植食者诱导的2,4-二羟基-7-甲氧基-1,4-苯并恶嗪-3-酮葡萄糖苷（2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside，DIMBOA-Glc）甲基化生成2-羟基-4,7-二甲氧基-1,4-苯并恶嗪-3-酮葡萄糖苷（2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside，HDMBOA-Glc）的过程，可提升玉米对鳞翅目幼虫的抗性；而较低的DIMBOA-Glc水平则利于蚜虫的繁殖。据此推测，玉米中被鳞翅目幼虫诱导的DIMBOA-Glc甲基转移酶活性，会促进蚜虫的生长。为验证该假说，研究人员利用17个遗传背景多样的玉米自交系，评估了甜菜夜蛾取食对玉米叶蚜子代繁殖量的影响。实验结果显示，在B73、Ki11、Ki3及Tx303四个自交系中，先前的甜菜夜蛾取食会提升蚜虫的子代繁殖量；而在Ky21、CML103、Mo18W及W22四个自交系中，该处理则会降低蚜虫的子代繁殖量。通过对B73×Ky21重组自交系（recombinant inbred lines，RIL）群体的该性状进行遗传定位，研究人员在玉米第1、7、10号染色体上鉴定到了显著的数量性状位点（quantitative trait loci，QTL）。该蚜虫抗性性状存在超亲分离现象：位于第1、7号染色体的Ky21等位基因，以及位于第10号染色体的B73等位基因，均可提升蚜虫的子代繁殖量。第1号染色体的QTL区域与一个包含3个玉米基因的基因簇重合，该簇编码可将DIMBOA-Glc转化为HDMBOA-Glc的苯并恶嗪O-甲基转移酶（benzoxazinoid O-methyltransferases）。基因表达分析与苯并恶嗪类物质含量测定结果表明，甜菜夜蛾诱导的该通路响应，会差异化调控B73与Ky21对玉米叶蚜的抗性。