Gibberellin-flavonoid crosstalk intensifies symbiotic nitrogen fixation in pea during maize-pea interspecific root interactions.

Abstract

Excessive synthetic nitrogen (N) fertilizer use threatens sustainable agriculture, highlighting the need to optimize symbiotic N fixation (SNF) in cereal/legume intercropping systems. Although interspecific root interactions (IRIs) may enhance SNF, the associated regulatory mechanisms remain unclear. A 3-yr field experiment showed that Zea mays/Pisum sativum intercropping can promote SNF and N accumulation. Furthermore, glasshouse root barrier and rhizobial inoculation experiments revealed that IRIs can enhance N accumulation via pea-rhizobia symbiosis. Mechanistically, IRIs increase nodule number and inhibit nodule senescence, which are accompanied by transcriptional reprogramming and altered phytohormone abundance (e.g. gibberellin). Exogenous paclobutrazol and gibberellin treatments confirmed that SNF enhancement during IRIs involves gibberellin synthesis. Exogenous gibberellin did not affect SNF-related advantages due to IRIs, indicating that IRIs autonomously optimize endogenous gibberellin to fine-tune SNF. Genetic evidence (silencing of PsGA20OX8 and PsCHS1-4, which affect gibberellin and flavonoid biosynthesis, respectively) and pharmacological evidence (complementation with exogenous gibberellin and flavonoid, respectively) demonstrated that crosstalk between the gibberellin and flavonoid increases nodule number and inhibits nodule senescence, thereby enhancing SNF. These findings support improving legume SNF via IRIs to optimize intercropping systems and promote sustainable agriculture development.