Proteomics insights into the basis of interspecific facilitation for maize (Zea mays) in faba bean (Vicia faba)/maize intercropping.

Faba bean/maize intercropping significantly promotes maize productivity in phosphorus-deficient soils. This has been attributed to the below-ground interactions including rhizosphere effects and spatial effects. Nevertheless, the molecular mechanisms underlying these interactions have been scarcely investigated. Here, three types of pots were used to distinguish the influences of rhizosphere effects vs. spatial effects. Phosphorus and nitrogen uptake of shoots, biomass, total root length, and root classification were evaluated between the three treatments. Quantitative RT-PCR and proteomics analyses were conducted to investigate the putative components in the molecular basis of these interactions. Quantitative RT-PCR results indicated that rhizosphere effects promoted maize phosphorus status at molecular levels. 66 differentially accumulated protein spots were successfully identified through proteomics analyses. Most of the protein species were found to be involved in phosphorus, nitrogen, and allelochemical metabolism, signal transduction, or stress resistance. The results suggest that rhizosphere effects promoted phosphorus and nitrogen assimilation in maize roots and thus enhanced maize growth and nutrient uptake. The reprogramming of proteome profiles suggests that rhizosphere effects can also enhance maize tolerance through regulating the metabolism of allelochemicals and eliciting systemic acquired resistance via the stimulation of a mitogen-activated protein kinase signal pathway. BIOLOGICAL SIGNIFICANCE: The results obtained contribute to a comprehensive understanding of the response of maize to the changes of rhizosphere condition influenced by the below-ground interactions in faba bean/maize intercropping at molecular levels. The identified protein species involved in nutrient metabolisms and stress resistance reveal the molecular basis underlying the major advantages of effective nutrient utilization and higher stress tolerance in legume/cereal intercropping systems. This work provides essential new insights into the putative components in the molecular basis of interspecific facilitation for maize in faba bean/maize intercropping.