JIA-2019-11

2465 XU Bing-qin et al. Journal of Integrative Agriculture 2019, 18(11): 2457–2471 HN1/HN2, and most of these DEGs belong to bHLH, WRKY, NAC, ERF, and MYB with the top five families accounting for almost 50% (Fig. 5-B and Appendix H). As expected, these TF families have common functions in drought-stress regulation. All TFs of four of these families were found up- regulated (90.8%), with only one gene down-regulated in HN1/HN2. Most of TFs are TFs, bHLH, is a family which serves as a regulator in foxtail millet development, and studies have shown that it might play a role in the control of ROS-mediated signaling thus linking drought adaptation to ROS signaling (Golldack et al . 2011). In this study, there were nine genes up-regulated and 13 genes down-regulated in DM1/DM2, compared to nine genes up-regulated and three genes down-regulated in HN1/HN2. These expression alterations under drought stress in the two cultivars indicated the potential functions of the TF-encoding genes in drought tolerance in foxtail millet. 3.7. Chlorophyll metabolism and photosynthesis responses to short-term drought stress The total chlorophyll levels, including Chl a and Chl b , were decreased by 25.94 and 14.89%, respectively, in DM and HN exposed to drought stress for 24 h compared with control 0 h (Fig. 6). Specifically, there were 19.39 and 25.94% decreases of Chl a and Chl b in DM. Similarly, 13.49 and 14.89% decreases of Chl a and Chl b in HN were estimated in 24 h drought treated leaves (Fig. 6). In the transcriptomic analysis, seven DEGs involved in the chlorophyll metabolism pathway were identified, of which two transcripts were up-regulated and five were down-regulated. Moreover, all DEGs related to Chl a synthesis were significantly down- regulated, including glutamate-1-semialdehyde (GSA), porphobilinogen deaminase (PBGD), and divinylreductase (DVR), and mostly found in HN (Fig. 6); whereas, two Fig. 6 The chlorophyll content and its metabolic pathways. A, the Chl a and Chl b contents change in osmotic-stress foxtail millet leaves of Damaomao (DM) and Hongnian (HN). B, chlorophyll metabolic pathway in osmotict-stress foxtail millet leaves. GSA, glutamate-1-semialdehyde; PBGD, porphobilinogen deaminase; DVR, divinyl chlorophyllide a 8-vinyl-reductase; CLH2, chlorophyllase-II; PAO, pheophorbide a oxygenase. Chl a Chl a Chl b Chl b 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 0 24 Chl a Chl a Chl b Chl b 0 0.2 0.4 0.6 0.8 1.0 1.2 0 24 Time (h) Time (h) HN DM Chl a and Chl b contents (mg g –1 FW) Chl a and Chl b contents (mg g –1 FW) A Biosynthesis −1.23 −1.00 −1.10 −1.38 1.27 −1.09 0.00 0.00 0.00 2.41 DM HN GSA PBGD PAO Glutanyl-tRNA ALA Uroporphyrinogen III Protoporphyrin IX ChlorophyII a DVR Mg-Protoporphyrin CLH2 Chlorophylide a Nonfluorescent chlorophyll catabolite (NCC) Choroplast B −10 −5 0 5 Log 2 FC Degradation