The Arabidopsis eIF4E1 regulates NRT1.1-mediated nitrate signaling at both translational and transcriptional levels.

Identifying new nitrate regulatory genes and illustrating their mechanisms in modulating nitrate signaling are of great significance for achieving the high yield and nitrogen use efficiency (NUE) of crops. Here, we screened a mutant with defects in nitrate response and mapped the mutation to the gene eIF4E1 in Arabidopsis. Our results showed that eIF4E1 regulated nitrate signaling and metabolism. Ribo-seq and polysome profiling analysis revealed that eIF4E1 modulated the amount of some nitrogen (N)-related mRNAs being translated, especially the mRNA of NRT1.1 was reduced in the eif4e1 mutant. RNA-Seq results enriched some N-related genes, supporting that eIF4E1 is involved in nitrate regulation. The genetic analysis indicated that eIF4E1 worked upstream of NRT1.1 in nitrate signaling. In addition, an eIF4E1-interacting protein GEMIN2 was identified and found to be involved in nitrate signaling. Further investigation showed that overexpression of eIF4E1 promoted plant growth and enhanced yield and NUE. These results demonstrate that eIF4E1 regulates nitrate signaling by modulating NRT1.1 at both translational and transcriptional levels, laying the foundation for future research on the regulation of mineral nutrition at the translational level.

Transepithelial Transport Characteristics of the Cholesterol- Lowing Soybean Peptide, WGAPSL, in Caco-2 Cell Monolayers.

Recent studies have shown that soybean protein and its peptides have cholesterol-lowering activities. However, it is not clear whether these peptides could overcome physiological barriers, such as phase II metabolism in gastrointestinal tract and poor permeability, to reach the blood stream in its intact form. Therefore, the transepithelial transport characteristics of soybean peptide Trp-Gly-Ala-Pro-Ser-Leu (WGAPSL) with cholesterol- lowering activity were investigated in Caco-2 cells. In this study; the transepithelial absorption of WGAPSL was studied using human intestinal Caco-2 cell monolayers. The results showed that WGAPSL had good stability (83.9% ±1.98%) after simulated gastric and intestinal digestion. During the apical (AP) side to basolateral (BL) side transport, WGAPSL was absorbed intact through Caco-2 cell monolayers with apparent permeability coefficient (Papp) values of 4.4 × 10-8 to 1.2 × 10-8 cm/s. Cytochalasin D loosened the tight junctions of Caco-2 cell monolayers and significantly (p < 0.05) improved the transport process. Sodium azide, wortmannin, and Gly-Pro had minimal effects on transport, demonstrating that the major transport route of WGAPVL was paracellular via tight junctions. Finally, LC-MS analysis showed that Gly-Ala-Pro (GAP) was the important part for the intact absorption of WGAPVL and Trp (W) was the most unstable amino acid residue.