Host-Dependent Endophytes as a Resilient Biological Reservoir: Niche-Specific Expansion and Holobiont Reassembly in Grapevine.

Plants and their endophytic microbiota form a functional holobiont, wherein host-dependent endophytes (HDEs) are proposed to serve as persistent microbial components associated with host continuity. Using long-term in vitro grapevine plantlets, we investigated HDE redistribution and reassembly across successive agar-based subcultures and during the transition to soil-based cultivation. Results showed that the initial tissue niche (shoot-tip versus root-base) imprinted a persistent compositional signature on HDE communities, with distinct cultivar-dependent effects. Numerous microbial amplicon sequence variants (ASVs) remained shared across agar-based and soil-based habitats, demonstrating high persistence of HDE-associated lineages. Bacterial communities exhibited marked plasticity, with plant-associated bacterial lineages contributing substantially to soil community assembly. Notably, 204 root-enriched bacterial ASVs, comprising 10.8-14.3% of the soil community, were recovered, revealing a robust "Root-Specific Legacy". Bacterial HDEs showed higher redistribution potential (43.3%), whereas fungal transfer was significantly lower (10.4%). Functional profiling suggested habitat-associated functional patterns, with the anaerobic phenotype enriched in soil and predicted enhancements in membrane transport, nucleotide metabolism, glycan biosynthesis, and biosynthesis of secondary metabolites in roots.