Seed endophytic bacteria are involved in metal adaptation of Orobanche lutea: community dynamics and plant growth promotion traits

Abstract

Background Parasitic plants are affected by various abiotic stressors including water and drought stress, fluctuations or extremes of temperature, salinity, mineral deficiencies or toxic concentrations of heavy metals in soils. While the molecular mechanisms and the ecological roles of these parasitic angiosperms have been well-studied, their responses to abiotic stress remain poorly understood. This study explores the relationship between environmental metal stress and the seed endophytic bacterial community of the holoparasitic plant Orobanche lutea Baumg. (Orobanchaceae). ResultsOur findings reveal significant shifts in microbial community composition across different environmental conditions, developmental stages and time points. Orobanche lutea seeds selectively accumulate metals such as Zn and Pb. Significant differences in the O. lutea seed microbial community composition suggest a strong influence of both, environmental conditions and plant developmental stages. Certain bacterial genera, including Bacillus, Paenibacillus, Pantoea, Okibacterium, Staphylococcus and Micromonospora were consistently detected across all samples, suggesting a vertically transmitted core microbiome. Notably, seed endophytic bacterial communities in O. lutea, respond dynamically to metal stress. Several isolated strains (e.g. Bacillus, Paenibacillus, Curtobacterium and Mictobacterium) showed high tolerance to Zn and Pb salts. However, elevated Zn and Pb concentrations in seeds do not promote the enrichment of metal-tolerant endophytes. Furthermore, metal stress appeared to increase the frequency of plant growth-promoting (PGP) traits within the seed microbiome supporting the idea that endophytes contribute to the adaptation of holoparasitic plants to heavy metal stress. Conclusions These results highlight the dynamic nature of seed-associated microbial communities under metal stress and underscore the critical role of seed endophytes in mediating the responses of holoparasitic plants to environmental challenges. The relationship between seed microbiome composition and metal exposure offers new insights of understanding stress resilience and developing microbial-based mitigation strategies.