Abstract

Key message McORA activates McHDR transcription to enhance aphid-induced ( E )-β-farnesene biosynthesis, conferring increased aphid resistance in German chamomile and providing a target for genetic improvement. German chamomile ( Matricaria chamomilla L.) is an annual medicinal plant whose essential oil is rich in sesquiterpenoids, including ( E )-β-farnesene ( E βF), chamazulene, nerolidol and α-bisabolol, which collectively exhibit antibacterial, anti-inflammatory, hypoglycemic, hypolipidemic, spasmolytic, and sedative activities. However, German chamomile is highly susceptible to aphid infestation, resulting in stunted growth, leaf chlorosis and curling, and premature senescence. Here, we demonstrate that E βF production can be induced by aphid-feeding, and that it exerts a repellent effect on aphids, as shown by Y-tube olfactometer choice assays. To elucidate the regulatory mechanism underlying E βF biosynthesis, we cloned the promoter of McHDR , a key gene in the E βF pathway, using Fusion Primer and Nested Integrated PCR (FPNI-PCR). Correlation analysis and yeast one-hybrid (Y1H) library screening identified McORA as a transcription factor that regulates McHDR , and full-length McORA cDNA was obtained using 5’/3’-RACE. McORA specifically bound the CAACA motif within the McHDR promoter and activated its transcription, as confirmed by Y1H point-to-point assays, dual-luciferase reporter assays and electrophoretic mobility shift assays (EMSA). Finally, transgenic hairy roots and virus-induced gene silencing (VIGS) in German chamomile leaves verified that McORA positively regulates McHDR expression and E βF accumulation, and aphid infestation experiments under natural conditions showed that McORA silencing significantly reduces aphid resistance. Taken together, these findings provide experimental evidence that E βF functions as an effective aphid-repellent and, for the first time, elucidate McORA -mediated transcriptional regulation of