Abstract
Many plant-associated fungi host endosymbiotic endobacteria with reduced genomes. While endobacteria play important roles in these tri-partite plant–
fungal–endobacterial systems, the active physiology
of fungal endobacteria has not been characterized
extensively by systems biology approaches. Here, we
use integrated proteomics and metabolomics to characterize
the relationship between the endobacterium
Mycoavidus sp. and the root-associated fungus
Mortierella elongata. In nitrogen-poor media, M. elongata
had decreased growth but hosted a large and
growing endobacterial population. The active endobacterium
likely extracted malate from the fungal
host as the primary carbon substrate for energy production
and biosynthesis of phospho-sugars,
nucleobases, peptidoglycan and some amino acids.
The endobacterium obtained nitrogen by importing a variety of nitrogen-containing compounds. Further,
nitrogen limitation significantly perturbed the carbon
and nitrogen flows in the fungal metabolic network.
M. elongata regulated many pathways by concordant
changes on enzyme abundances, post-translational
modifications, reactant concentrations and allosteric
effectors. Such multimodal regulations may be a general
mechanism for metabolic modulation.