HighlightThis study identified the novel gene UAP1 in rice. UAP1 is involved in early leaf senescence and defence responses.

To find a way to promote the rate of carbon flux and further improve the photosynthetic rate in rice, two CO2-transporting and fixing relevant genes, Ictb and FBP/Sbpase, which were derived from cyanobacteria with the 35SCaMV promotor in the respective constructs, were transformed into rice. Three homologous transgenic groups with Ictb, FBP/Sbpase and the two genes combined were constructed in parallel, and the functional effects of these two genes were investigated by physiological, biochemical and leaf anatomy analyses. The results indicated that the mesophyll conductance and net photosynthetic rate were higher at approximately 10.5–36.8% and 13.5–34.6%, respectively, in the three groups but without any changes in leaf anatomy structure compared with wild type. Other physiological and biochemical parameters increased with the same trend in the three groups, which showed that the effect of FBP/SBPase on improving photosynthetic capacity was better than that of ICTB and that there was an additive effect in ICTB+FBP/SBPase. ICTB localized in the cytoplasm, whereas FBP/SBPase was successfully transported to the chloroplast. The two genes might show a synergistic interaction to promote carbon flow and the assimilation rate as a whole. The multigene transformation engineering and its potential utility for improving the photosynthetic capacity and yield in rice were discussed.

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Ammonium toxicity in plants is considered a global phenomenon, but the primary mechanisms remain poorly characterized. Here, we show that although the addition of potassium or nitrate partially alleviated the inhibition of rice seedling root growth caused by ammonium toxicity, the combination of potassium and nitrate clearly improved the alleviation, probably via some synergistic mechanisms. The combined treatment with potassium and nitrate led to significantly improved alleviation effects on root biomass, root length, and embryonic crown root number. The aberrant cell morphology and the rhizosphere acidification level caused by ammonium toxicity, recovered only by the combined treatment. RNA sequencing analysis and weighted gene correlation network analysis (WGCNA) revealed that the transcriptional response generated from the combined treatment involved cellulose synthesis, auxin, and gibberellin metabolism. Our results point out that potassium and nitrate combined treatment effectively promotes cell wall formation in rice, and thus, effectively alleviates ammonium toxicity.