Interkingdom signaling dynamics in the cereal holobiont: microbiome-mediated pathways to drought resilience

Root-associated microbiomes are increasingly recognized as important contributors to drought adaptation in cereal crops. Rather than functioning solely through improved nutrient acquisition, beneficial microorganisms can reshape host stress responses by modulating interconnected signaling, metabolic, transcriptional, and epigenetic pathways. Emerging evidence suggests that the plant-microbiome interactions operate through complex interkingdom signaling networks that coordinate root physiology, hormonal regulation, reactive oxygen species homeostasis, and stress-responsive gene expression, ultimately reinforcing drought resilience. However, current understanding of microbiome-mediated drought adaptation remains fragmented across ecological, omics, and molecular signaling perspectives. In this review, we synthesize current knowledge on microbiome-mediated signaling mechanisms underlying drought resilience in cereals from a holobiont-oriented perspective, in which plants and their root-associated microbiomes are viewed as integrated adaptive systems. We discuss how drought-responsive microbiomes influence plant adaptation through genomic and functional complementarity, multi-omics reprogramming, and modulation of core regulatory hubs, including protein kinases, transcription factors, phytohormones, reactive oxygen species, small signaling peptides, miRNAs, lncRNA-associated networks, and epigenetic regulation. Finally, we highlight major mechanistic gaps, technological challenges, and emerging opportunities for microbiome-informed engineering strategies aimed at improving cereal drought resilience.