Transcription factor McORA activates McHDR to enhance aphid-repelling (E)-β-farnesene biosynthesis in Matricaria...

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 (EβF), 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 EβF 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 EβF biosynthesis, we cloned the promoter of McHDR, a key gene in the EβF 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 EβF accumulation, and aphid infestation experiments under natural conditions showed that McORA silencing significantly reduces aphid resistance. Taken together, these findings provide experimental evidence that EβF functions as an effective aphid-repellent and, for the first time, elucidate McORA-mediated transcriptional regulation of McHDR and its influence on EβF biosynthesis in German chamomile, thereby highlighting a potential genetic engineering strategy to enhance aphid resistance.