Effects of varying temperature on rhythmic expression of abiotic stress-responding genes in Tibetan hulless barley

Tibetan hulless barley (Hordeum vulgare L. var. nudum hook. f.) is an oriental barley cultivar that is primarily grown in the regions around the Tibet–Qinghai plateau. The circadian clock is an endogenous time-keeping system that plays important roles in modulating the tolerance of plants to abiotic stresses. While the manner in which the circadian clock regulates the response of plants to temperature stress has been investigated in previous reports, few studies have focused on the adaptation mechanisms of hulless barley to different temperature conditions. Here, we analyzed the rhythmic expression patterns of the circadian clock genes and stress-responding genes of the hulless barley under different temperature conditions. This work showed that the diurnal expression rhythm of hulless barley clock genes can be kept stable at a constant temperature of 25 °C or suddenly drop by 10–15 °C, but suddenly drop by 20–5 °C, this rhythm expression pattern will be disordered. By analyzing the temporal expression pattern of stress-resistance genes, we found that major stress-responding genes in the hulless barley seedlings maintained their expression rhythms at constant 25 °C, but when they were transferred to 15 or 5 °C, their expression patterns became arrhythmic. Interestingly, the stress-responsive genes of HvCBL4 kept their diurnal rhythms in expression at different temperature conditions. These results unveiled that both the external time cues generated by environmental light changes and the internal time cues from unknown endogenous circadian clock components control the rhythmic expression of HvCBL4 under cold stress conditions in Tibetan hulless barley. This work contributes to further research on the possible mechanisms of influence of the circadian clock on cold-stress resistance in cereal crops.