Carotenoid Cleavage Dioxygenase 8 Enhances Interspecific Facilitation in Maize‐Soybean Intercropping via Arbuscular Mycorrhiza Symbiosis Under Phosphate Limitation

Carotenoid Cleavage Dioxygenase 8 (CCD8) regulates strigolactone (SL) biosynthesis, which mediates the establishment of arbuscular mycorrhiza fungal (AMF) symbiosis. This symbiosis makes a major contribution in nutrient uptake, thereby improving crop productivity, mostly without the need for specific inoculation. Quantifying the extent of this contribution in typical intercropping systems remains challenging. A pot experiment was conducted using ZmCCD8 knockout (zmccd8), overexpression (ZmCCD8-OE), and wild type (WT) maize lines, grown in sole cropping or intercropping with soybean under low phosphate (LP) and control conditions. Intercropped ZmCCD8-OE and soybean showed a 61.9% higher overyielding effect, partially attributed to a 72.7% greater AMF colonisation rate in ZmCCD8-OE than WT counterparts under LP. Together with the greater root, AMF promoted P accumulation by 58% and 35% in the ZmCCD8-OE shoot and root, respectively. Conversely, intercropped zmccd8 conferred negative impacts under LP, corresponding to 47.6% and 63.4% less overyielding and AMF colonisation, respectively. Consistent with these results was differential expression of genes (CCD8, D14, CCaMK, CYCLOPS, RAM1, PT6/PT8) regulating AMF symbiosis and P uptake in maize and soybean. Collectively, ZmCCD8 enhances interspecific facilitation by stimulating root growth and AMF symbiosis, providing a genetic approach for higher crop productivity in intercropping systems without inoculation.