Epigenetic and metabolic regulation of drought stress memory in maize: from molecular mechanisms to field-applicable priming strategies
Maize ( Zea mays L.) is highly vulnerable to recurrent water deficits, particularly during vegetative-to-reproductive transition. Although physiological acclimation to drought is well documented, the capacity of maize to establish and transmit drought stress memory represents an underexplored frontier for climate-resilient agriculture. This review synthesizes the crop-specific epigenetic and metabolic mechanisms that govern drought priming and memory persistence in maize. We examine how initial osmotic stress triggers localized regulatory cascades, focusing on histone modifications (H3K4me2, H3K9ac, H3K27me3, and H3K36me3), DNA methylation dynamics, and transposable element regulation across the maize genome, where transposable elements comprise approximately 85% of the nuclear DNA. We detail the metabolic memory engram, which encompasses proline biosynthesis, carbon-nitrogen reallocation, and photosynthetic adjustments. Concurrently, we evaluate practical agronomic priming strategies—including hydropriming, osmopriming with CaCl 2 and PEG, chitosan priming, hormone priming (melatonin, SA, GA 3 ), and nanopriming—alongside emerging epigenetic biomarker screening platforms to identify drought-tolerant germplasms. By integrating molecular circuitry with field-applicable priming, this framework charts pathways for optimizing the memory yield equation. We explicitly identify critical knowledge gaps, including the limited direct measurements of proline biosynthetic enzyme kinetics (P5CS/P5CR) in primed versus unprimed maize and the largely uncharacterized phosphorylation states of PEPC under priming conditions, providing a roadmap for future research.