Effects of DCMU on anthocyanin synthesis genes and its related signals in C₄-pepc gene overexpressed rice under drought conditions

Anthocyanins are important antioxidant materials that protects plant from damage by reactive oxygen species (ROS). Especially under adverse conditions, the regulation of sucrose in plants depends on its ability to induce anthocyanin accumulation. To determine the intrinsic relationship between photosynthetic and anthocyanin regulated pathways for C₄-phosphoenolpyruvate carboxylate (PEPC, EC 4.1.1.31) gene overexpressed rice (PC) in drought conditions, PC and untransformed wild-type (WT) were treated with 50 μmol·L-1 photosynthetic inhibitor DCMU for 1 h and the performance of the rice seedlings at 4-5 leaf stage observed under 12% PEG-6000 simulated drought. The results showed that DCMU pretreatment significantly reduced relative water contents of WT and PC under simulated 12% PEG-6000 drought condition, and relative water content of PC was significantly higher than that of WT. The anthocyanin content was higher in PC than in WT under 12% PEG-6000 simulated drought or drought plus DCMU pretreatment. 12% PEG-6000 simulated drought decreased anthocyanin contents of PC and WT, while DCMU pretreatment alleviated this effect. Compared with 12% PEG-6000, DCMU plus 12% PEG-6000 significantly inhibited net photosynthetic rate, stomatal conductance, intercellular CO₂ and carboxylation efficiency of the two rice lines, but these parameters of PC lines were significantly higher than those of WT lines. Then DCMU plus 12% PEG-6000 down-regulated endogenous sucrose content of the two materials, but sucrose content of PC lines was significantly higher than that of WT lines. Further studies showed that higher sucrose level in PC was associated with higher expression levels of transcriptional factors of bHLH (OsB1, OsB2), R2R3-MYB (OsC1), COP1 (constitutively photomorphogenic 1), HY5 (elongated hypocotyl 5), OsPAL, OsCHI, OsCHS, OsF3H, OsF3'H, OsDFR and OsANS, which resulted in synthesizing more anthocyanin to improve water retention capacity. In addition, PC rice sensed drought signals through NO and Ca²⁺, which participated in the regulation of transcription factors, regulation of anthocyanin synthesis gene, synthesis of more anthocyanin and thereby enhanced PC rice response to drought stress. This enhanced water retention capacity, stabilized photosynthetic capacity and resisted drought. Therefore, it was beneficial in molecular breeding of "C₄ Rice" to study the symphony between high yield and plant resistance.