Endosphere

Endosphere refers to the internal tissue compartments of a plant that harbor endophytic microorganisms, distinct from the rhizosphere (the soil zone around roots) and the phyllosphere (above-ground surfaces). Endophytes include bacteria, fungi, archaea, and yeasts that live inside plant tissues for at least part of their life cycle, often without causing disease.

Entry and colonization occur when microbes gain access through natural openings, wounds, or root hairs. Once inside, they may inhabit intercellular spaces or vascular tissues within roots, stems, leaves, or seeds. The endosphere provides a relatively protected environment with plant-derived nutrients, supporting diverse microbial communities that can persist across plant generations or environmental conditions.

Composition and variation of endophytic communities depend on host species, tissue type, developmental stage, and environment. Bacterial groups commonly detected in the endosphere include members of Proteobacteria, Firmicutes, and Actinobacteria, while fungal endophytes often belong to Ascomycota and Basidiomycota. Some endophytes are widespread across plant hosts, whereas others are highly specific to particular species or tissues.

Functions and significance: Many endophytes contribute to host fitness by producing phytohormones, solubilizing nutrients, or, in some cases, fixing nitrogen. They can enhance drought tolerance, salt tolerance, and disease resistance through various mechanisms, including priming plant defenses. However, the relationship is not universally beneficial; some endophytes can become opportunistic pathogens under stress or inappropriate conditions.

Study and applications: Endosphere research uses surface sterilization of plant tissues followed by culture-based isolation or culture-independent sequencing (for example, 16S rRNA gene analysis for bacteria and ITS sequencing for fungi). Understanding endophytic communities supports efforts in sustainable agriculture, including biocontrol and biofertilization strategies.