JIA-2019-11

2469 XU Bing-qin et al. Journal of Integrative Agriculture 2019, 18(11): 2457–2471 against oxidative damage to enhance the environmental stress tolerance. The dismutation of the superoxide anion by superoxide dismutase (SOD) to yield H 2 O 2 , and the activation and deactivation of H 2 O 2 by peroxidases (POD) play essential roles in the regulation of reactive oxygen species (Sairam et al . 2005). In the present study, the MDA accumulation after 24 h drought stress of DM and HN reflected the elevated level of oxidative damage. Whereas plants accrued different antioxidative enzymes to resist drought severity, the transcriptomic investigation revealed that enzymes in the GSH-AsA cycle, including ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR), and GST drought-responsive antioxidative defense systems in DM and HN were activated. 4.3. ABA and JA metabolism changes in two genotypes under drought stress Under drought, endogenous contents of ABAand JA, which are generally regarded as stress hormones that regulate gene expression to enable plant acclimation to stress, significantly increased after 24 h. In this report, ABA and JA levels rose conspicuously as the result of increased synthesis, and the synthesis-related genes identified, including ZEP, NCED, and AAO in ABA synthesis and AOS, AOC, and OPR in JA synthesis, were up-regulated. It has been proven that NCED overexpression in transgenic plants can significantly increase the accumulation of ABA in leaves and impart improved drought tolerance (Bao et al . 2016). Specially, the transcriptomic investigation revealed that the genes encoding protein SnRK2, and all of groupAof PP2Cs that are associated with ABA signal transduction were up- regulated in both cultivars. In the JA signaling pathway, jasmonate-zim domain proteins (JAZ) were also significantly up-regulated in the two cultivars under drought stress. 4.4. Compatible organic solutes metabolism changes in two genotypes under drought stress As one of the main effects of drought stress and tolerance strategies in foxtail millet, the overproduction of different types of compatible organic solutes, including amino acids (e.g., proline) and soluble sugars (e.g., fructans, trehalose and sucrose), under 24 h drought stress was very apparent (Fig. 1). In this study, the synthesis of osmolytes, permitting an osmotic adjustment, or the net accumulation of solutes to maintain the favorable water potential gradient and protect cellular turgor (Bray), were also significantly up-regulated. These included the three DGEs encoding two important proline synthesis OAT and P5CS (Fig. 7), and two genes encoding trehalose-phosphate phosphatase (Table 3). In contrast, one gene related to proline degradation in HN was down-regulated, promoting the accumulation of proline. 5. Conclusion Our study surveyed physiological changes and transcriptome alterations in the seedling stage leaves to reveal transcriptomic responses of foxtail millet to short-term (24 h) drought stress in two cultivars, DMand HN. The physiological data, such as the decrease of RWC and the increase of MDA, proline, and ABA in 24 h drought stress, indicated that foxtail millet leaves had sensed the drought at 24 h and reacted quickly to it. From the deep transcriptomic survey in the two cultivars, we found that foxtail millet launches a Fig. 9 Linear correlation analysis using Pearson correlation coefficient ( r ) of fold change data between qRT-PCR and fold change (FC) of genes. ● ● ● ●● ● ● ● ● Correlation=0.968 −4 −2 0 2 −2 0 2 4 log 2 FC from RNA-seq data log 2 FC from RT−PCR data Scatter plot DM1/DM2 ● ● ● ● ● ● ● ● ● Correlation=0.885 −2.5 0.0 2.5 −7.5 −5.0 −2.5 0.0 2.5 5.0 log 2 FC from RNA-seq data log 2 FC from RT-PCR data Scatter plot HN1/HN2