Molecular mechanisms of nitric oxide regulating high photosynthetic performance of wheat plants in waterlogging at flowering

Nitric oxide (NO) positively contributes to maintaining a high photosynthetic rate in waterlogged-wheat plants by maintaining high stomatal conductance (gs), mesophyll conductance (gm), and electron transport rates in PSII (J). However, the molecular mechanisms underlying the synergistic regulation of photosynthetic characteristics during wheat waterlogging remain unclear. Pot experiments were conducted with two cultivars: Yangmai15 (YM15: high waterlogging-tolerance capacity) and Yangmai24 (YM24: conventional waterlogging-tolerance capacity). The 2 cm waterlogging depth treatment (WL), exogenous spraying of NO every two days in the WL treatment (WLsnp), and suitable soil water content treatment (CK) were established during the flowering stage for eight consecutive days. RNA-seq, weighted gene co-expression network analysis (WGCAN), and protein interaction analysis were performed on the 8th day to screen key genes that maintain high photosynthetic performance in waterlogged-wheat plants. The results indicated that cultivar YM24 and YM15 contained 10411 and 10582 differentially expressed genes (DEGs), respectively. The WL treatment had obviously higher DEGs than the WLsnp treatment compared to the CK treatment. Based on the WGCAN method, the DEGs were clustered into eight modules and correlated significantly with the four photosynthetic parameters mentioned above (P < 0.05). Only the DEGs in the ivory module (571) enriched the photosynthetic pathways among the eight modules. In the ivory module, 10 hub genes, including TaB1274F11.29-1, TaT6H20.190, TaOSNPB_100100300, TaLHCB, TaPSAG, TaCAP10B, TaFAD7A-1, TaCAB3C, TaT27G7, and TaF24G24.140, were screened using the coexpression network method because the genes exhibited similar variation trends with gs, gm, or J across the three water treatments and both cultivars. TaLHCB and TaCAP10B exhibited significant linear relationships with the three parameters of gs, gm, and J (P < 0.05). Consequently, TaLHCB and TaCAP10B genes are defined as waterlogging-resistance genes due to the synergistic regulation of photosynthetic characteristics in waterlogging. Both genes were significantly down-regulated in the WL treatment compared to CK treatment in both cultivars. However, there was no significant difference between WLsnp and CK treatments for the genes in the cultivar YM15. These results suggest that the positive effects of spraying NO with high waterlogging resistance capacities are linked to maintaining high expression levels of key genes and obtaining high photosynthetic characteristics during waterlogging, particularly for cultivars with high waterlogging resistance.