Integration of the metabolome and transcriptome reveals the mechanism of resistance to low nitrogen supply in wild bermudagrass (Cynodon dactylon (L.) Pers.) roots

Comprehensive Transcriptomic and Metabolic Profiling of Agrobacterium-tumefaciens-Infected Immature Wheat Embryos

The transformation efficiency (TE) was improved by a series of special chemical and physical methods using immature embryos from the cultivar Fielder, with the PureWheat technique. To analyze the reaction of immature embryos infected, which seemed to provide the necessary by Agrobacterium tumefaciens in PureWheat, a combination of scanning electron microscopy (SEM), complete transcriptome analysis, and metabolome analysis was conducted to understand the progress. The results of the SEM analysis revealed that Agrobacterium tumefaciens were deposited under the damaged cortex of immature embryos as a result of pretreatment and contacted the receptor cells to improve the TE. Transcriptome analysis indicated that the differentially expressed genes were mainly enriched in phenylpropanoid biosynthesis, starch and sucrose metabolism, plant-pathogen interaction, plant hormone signal transduction, and the MAPK (Mitogen-activated protein kinase) signaling pathway. By analyzing the correlation between differentially expressed genes and metabolites, the expression of many genes and the accumulation of metabolites were changed in glucose metabolism and the TCA cycle (Citrate cycle), as well as the amino acid metabolism; this suggests that the infection of wheat embryos with Agrobacterium is an energy-demanding process. The shikimate pathway may act as a hub between glucose metabolism and phenylpropanoid metabolism during Agrobacterium infection. The downregulation of the F5H gene and upregulation of the CCR gene led to the accumulation of lignin precursors through phenylpropanoid metabolism. In addition, several metabolic pathways and oxidases were found to be involved in the infection treatment, including melatonin biosynthesis, benzoxazinoid biosynthesis, betaine biosynthesis, superoxide dismutase, and peroxidase, suggesting that wheat embryos may be under the stress of Agrobacterium and, thus, undergo an oxidative stress response. These findings explore the physiological and molecular changes of immature embryos during the co-culture stage of the PureWheat technique and provide insights for Agrobacterium-mediated transgenic wheat experiments.

Effects of low nitrogen supply on nitrogen uptake, assimilation and remobilization in wild bermudagrass

The natural mechanism of underlying the low nitrogen (N) tolerance of wild bermudagrass (Cynodon dactylon (L.) Pers.) germplasm was important for reducing N fertilizer input to turf while also maintaining acceptable turf quality. The growth, N uptake, assimilation and remobilization of two wild bermudagrass accessions (C291, low N tolerant and C716, low N sensitive) were determined under low N (0.5 mM) and control N (5 mM) levels. C291 exhibited lower reduction in shoot and plant dry weight than C716. Furthermore, C291 presented a lower decrease in ¹⁵NO₃^- influx compared with C716, maintained its root dry weight and root surface and showed obviously enhanced CyNRT2.2 and CyNRT2.3 expression resulting in higher shoot NO₃^--N content than the control. Moreover, in C291, nitrate reductase (NR) activity had no significant difference with control, and cytosolic glutamine synthetase (GS1) protein content, glutamate synthetase (GOGAT) activity and glutamate dehydrogenase (GDH) activity higher than control, result in the soluble protein and free amino acid contents in the shoots did not differ compared with that in the control under low N conditions. Overall, the low N tolerant wild bermudagrass accessions adopted a low N supply based on improved root N uptake ability to achieve more nitrate to kept shoot N assimilation, and meanwhile increased N remobilization in the shoots, thereby maintaining a better N status in bermudagrass. The findings may help elucidate the low N tolerance mechanisms in bermudagrass and therefore facilitate genetic improvement of N use efficiency aiming to promote low-input turfgrass management.

Differential Metabolic Responses of Lettuce Grown in Soil, Substrate and Hydroponic Cultivation Systems under NH4+/NO3- Application

Nitrogen (N) is an essential element for plant growth and development. The application of a balanced and optimal amount of N is required for sustainable plant yield. For this, different N sources and forms are used, that including ammonium (NH4+) and nitrate (NO3-). These are the main sources for N uptake by plants where NH4+/NO3- ratios have a significant effect on the biomass, quality and metabolites composition of lettuce grown in soil, substrate and hydroponic cultivation systems. A limited supply of N resulted in the reduction in the biomass, quality and overall yield of lettuce. Additionally, different types of metabolites were produced with varying concentrations of N sources and can be used as metabolic markers to improve the N use efficiency. To investigate the differential metabolic activity, we planted lettuce with different NH4+/NO3- ratios (100:0, 75:25, 50:50, 25:75 and 0:100%) and a control (no additional N applied) in soil, substrate and hydroponic cultivation systems. The results revealed that the 25% NH4+/75% NO3- ratio increased the relative chlorophyll contents as well as the biomass of lettuce in all cultivation systems. However, lettuce grown in the hydroponic cultivation system showed the best results. The concentration of essential amino acids including alanine, valine, leucine, lysine, proline and serine increased in soil and hydroponically grown lettuce treated with the 25% NH4+/75% NO3- ratio. The taste and quality-related compounds in lettuce showed maximum relative abundance with the 25% NH4+/75% NO3- ratio, except ascorbate (grown in soil) and lactupicrin (grown in substrate), which showed maximum relative abundance in the 50% NH4+/50% NO3- ratio and control treatments, respectively. Moreover, 1-O-caffeoylglucose, 1,3-dicaffeoylquinic acid, aesculetin and quercetin-3-galactoside were increased by the application of the 100% NH4+/0% NO3- ratio in soil-grown lettuce. The 25% NH4+/75% NO3- ratio was more suitable in the hydroponic cultivation system to obtain increased lettuce biomass. The metabolic profiling of lettuce showed different behaviors when applying different NH4+/NO3- ratios. Therefore, the majority of the parameters were largely influenced by the 25% NH4+/75% NO3- ratio, which resulted in the hyper-accumulation of health-promoting compounds in lettuce. In conclusion, the optimal N applications improve the quality of lettuce grown in soil, substrate and hydroponic cultivation systems which ultimately boost the nutritional value of lettuce.