Differential cold stress intensities drive unique morphological and transcriptomic changes in Zea mays root hairs

Maize seedlings grown in temperate climates often encounter suboptimal temperatures that delay seedling establishment and reduce crop productivity. While research commonly treats cold stress as a uniform phenomenon, the nuances between moderate chilling and more extreme cold have rarely been disentangled. Dissecting these distinct temperature thresholds will uncover the adaptive strategies essential for maize resilience under varying low-temperature conditions. We investigated how mild (16 °C/12 °C) and severe (10 °C/6 °C) cold stress intensities modulate maize root hair development by integrating phenotypic observations with transcriptome profiling. Mild cold imposed partial inhibition on both primary root and hair growth. Mild cold stress induced fewer differentially expressed genes, mostly downregulated, affecting multiple processes including cell wall remodeling, while severe cold stress completely inhibited hair elongation and triggered a broader transcriptional reprogramming, highlighted by strong induction of peroxidases and pronounced changes in hormone signaling cascades (auxin, jasmonate, ethylene, cytokinin). While mild cold still maintained limited root hair elongation, severe cold repressed key root hair developmental regulators (e.g., rhd6, rsl4) and auxin transporters. This study demonstrated that maize root hairs respond to cold stress in a severity-dependent manner. Mild cold triggers adaptive remodeling that preserves limited growth, while severe cold prioritizes stress defense, culminating in more pronounced morphological inhibition. By defining the transcriptomic and morphological changes linked to each cold intensity, this study provides novel insights that could be applied for breeding strategies aimed at strengthening early seedling vigor and cold resilience in maize.