ZmHDS1 Confers Tolerance to Cold Stress in Maize Seedlings

Cold stress severely limits the productivity of maize, especially in Northeast China. Hydroxymethylbutenyl diphosphate synthase (HDS) is a key enzyme in the methylerythritol phosphate (MEP) pathway, which is responsible for the generation of precursors for carotenoid biosynthesis, thereby playing a central role in facilitating the cellular response to stress. In the present study, virus-induced gene silencing (VIGS)-mediated ZmHDS1 silencing on the B73 background led to enhanced cold stress sensitivity, as evidenced by growth retardation, leaf shriveling, disrupted Kranz anatomy, elevated reactive oxygen species (ROS) accumulation, impaired antioxidant enzyme activity, increased membrane lipid peroxidation, and reduced photosynthetic performance. Hormonal profiling revealed that ZmHDS1 silencing decreased the content of indole-3-acetic acid (IAA), gibberellin (GA4), and abscisic acid (ABA) and disrupted ABA signaling. Furthermore, ZmHDS1 silencing reduced the chlorophyll content, Rubisco activity, and ZmRCA (Rubisco activase) expression and caused a more severe reduction in carotenoid levels and the transcriptional suppression of the entire carotenoid biosynthetic gene network. Collectively, ZmHDS1 acts as a key component of the MEP pathway that contributes to maize cold tolerance by coordinating antioxidant defense, phytohormone homeostasis, photosynthetic maintenance, and carotenoid metabolism. These findings highlight the importance of the MEP pathway as a whole in cold adaptation. Disruption of ZmHDS1 impairs these interconnected protective mechanisms, rendering maize highly susceptible to cold-induced damage.