Differentially expressed ZmASR genes associated with chilling tolerance in maize (Zea mays) varieties.

The ABA-stress-ripening (ASR) gene is an abiotic stress-response gene that is widely present in higher plants. The expression of ASR was recently shown to effectively improve plant tolerance to several abiotic stresses. However, the role of ASR during chilling stress in maize (Zea mays L.) is unclear. In this study, we tested two maize varieties under chilling treatment. Our results showed that Jinyu 5 (JY5), a chilling-sensitive variety, had lower maximum PSII efficiency (Fv/Fm) and higher lipid peroxidation levels than Jidan 198 (JD198) under chilling conditions. At the same time, the enzymes superoxide dismutase (SOD) and peroxidase (POD) were more active in JD198 than in JY5 under chilling conditions. In addition, exogenous ABA spray pretreatments enhanced the chilling tolerance of maize, showing results such as increased Fv/Fm ratios, and SOD and POD activity; significantly reduced lipid peroxidation levels and increased expression of ZmASR1 in both JD198 and JY5 under chilling conditions. Moreover, when the ZmASR1 expression levels in the two maize varieties were compared, the chilling-sensitive line JY5 had significantly lower expression in both the leaves and roots than JD198 under chilling stress, indicating that the expression of ZmASR1 is a chilling response option in plants. Furthermore, we overexpressed ZmASR1 in JY5; this resulted in enhanced maize chilling tolerance, which reduced the decreases in Fv/Fm and the malondialdehyde content and enhanced SOD and POD activity. Overall, these results suggest that ZmASR1 expression plays a protective role against chilling stress in plants.