College of Agronomy, Shanxi Agricultural University, Taigu, Jinzhong 030801, China.
Int J Mol Sci. 2023 Jul 18;24(14):11590. doi: 10.3390/ijms241411590.
Low-temperature stress limits the growth and development of foxtail millet. Freezing stress caused by sudden temperature drops, such as late-spring coldness, often occurs in the seedling stage of foxtail millet. However, the ability and coping strategies of foxtail millet to cope with such stress are not clear. In the present study, we analyzed the self-regulatory mechanisms of freezing stress in foxtail millet. We conducted a physiological study on foxtail millet leaves at -4 °C for seven different durations (0, 2, 4, 6, 8, 10, and 12 h). Longer freezing time increased cell-membrane damage, relative conductance, and malondialdehyde content. This led to osmotic stress in the leaves, which triggered an increase in free proline, soluble sugar, and soluble protein contents. The increases in these substances helped to reduce the damage caused by stress. The activities of superoxide dismutase, peroxidase, and catalase increased reactive oxygen species (ROS) content. The optimal time point for the response to freezing stress was 8 h after exposure. The transcriptome analysis of samples held for 8 h at -4 °C revealed 6862 differentially expressed genes (DEGs), among which the majority are implicated in various pathways, including the starch and sucrose metabolic pathways, antioxidant enzyme pathways, brassinolide (BR) signaling pathway, and transcription factors, according to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment. We investigated possible crosstalk between BR signals and other pathways and found that BR signaling molecules were induced in response to freezing stress. The beta-amylase (BAM) starch hydrolase signal was enhanced by the BR signal, resulting in the accelerated degradation of starch and the formation of sugars, which served as emerging ROS scavengers and osmoregulators to resist freezing stress. In conclusion, crosstalk between BR signal transduction, and both starch and sucrose metabolism under freezing stress provides a new perspective for improving freezing resistance in foxtail millet.
低温胁迫限制了谷子的生长和发育。突降的低温如晚春寒，常发生在谷子幼苗期，这会导致冷冻胁迫。然而，谷子应对这种胁迫的能力和应对策略尚不清楚。在本研究中，我们分析了谷子应对冷冻胁迫的自我调节机制。我们对谷子叶片在-4°C下进行了 7 个不同时间（0、2、4、6、8、10 和 12 h）的生理研究。较长的冷冻时间会增加细胞膜损伤、相对电导率和丙二醛含量。这导致叶片渗透胁迫，引发游离脯氨酸、可溶性糖和可溶性蛋白含量增加。这些物质的增加有助于减轻胁迫造成的损伤。超氧化物歧化酶、过氧化物酶和过氧化氢酶的活性增加了活性氧（ROS）的含量。对冷冻胁迫的最佳响应时间点是暴露后 8 h。在-4°C下放置 8 h 的样品的转录组分析显示，有 6862 个差异表达基因（DEGs），其中大多数参与各种途径，包括淀粉和蔗糖代谢途径、抗氧化酶途径、油菜素内酯（BR）信号途径和转录因子，根据基因本体论（GO）和京都基因与基因组百科全书（KEGG）富集分析。我们研究了 BR 信号与其他途径之间可能的串扰，发现 BR 信号分子在受到冷冻胁迫时被诱导。BR 信号增强了β-淀粉酶（BAM）淀粉水解酶信号，导致淀粉快速降解并形成糖，糖作为新兴的 ROS 清除剂和渗透调节剂，抵抗冷冻胁迫。总之，BR 信号转导与冷冻胁迫下淀粉和蔗糖代谢之间的串扰为提高谷子的抗冻性提供了新的视角。
