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The regulation of plant gene expression by nitrate is a complex regulatory process. Here, we identified 90 GARP family genes in apples by genome-wide analysis. As a member of the GARP gene family, the expression of MdHHO3 (Malus domestica HYPERSENSITIVITY TO LOW PHOSPHATE-ELICITED PRIMARY ROOT SHORTENING1 HOMOLOG 3) is upregulated under N (nitrogen) supply. The results of DNA-binding site analysis and electrophoretic mobility shift assays (EMSA) showed that MdHHO3 binds to the motif-containing GAATC. Furthermore, MdHHO3 binds to its promoter sequence and inhibits its activity. In addition, the overexpression of MdHHO3 in apple calli resulted in less accumulation of nitrate in 35S:MdHHO3-GFP calli and downregulated the expression of the nitrate transport-related genes but upregulated the expression of the nitrate assimilation-related genes. Similarly, the expression of the nitrate transport-related genes was downregulated and the expression of the nitrate assimilation-related genes was upregulated in MdHHO3 overexpression Arabidopsis and tobacco plants. Interaction experiments showed that MdHHO3 could bind to the promoter MdNRT2.1 (NITRATE TRANSPORTER 2.1) and negatively regulate its expression. Moreover, the exposure of MdHHO3-overexpressing Arabidopsis and tobacco to nitrate deficiency resulted in an early senescence phenotype as compared to the WT plants. These results show that MdHHO3 can not only negatively regulate nitrate accumulation in response to nitrate but also promote early leaf senescence under nitrate deficiency. This information may be useful to further reveal the mechanism of the nitrate response and demonstrates that nitrate deficiency induces leaf senescence in apples.

BACKGROUND: The role of CO and adsorption sequence of CO and N 2 O in the adsorption and reduction of N 2 O on char was investigated based on density functional theory at the M06-2X/6-311G(d) theoretical level. This study lays a foundation for reaction mechanisms of the influence of CO on heterogeneous N 2 O reduction on char. RESULTS: Zigzag and armchair models were used as char models. The first adsorption of CO increases the limiting-step energy barrier of the reaction by 44.5 kJÁmol −1 compared with the first adsorption of N 2 O for zigzag char. However, the adsorption sequence does not have an effect for armchair char. The rate-limiting steps of the overall reaction for zigzag and armchair char models occur in the stages of N 2 O adsorption and N 2 O reduction, respectively. The introduction of CO has little effect on the N 2 O adsorption stage but increases the energy barrier of the N 2 O reduction stage. During the reduction of N 2 O on coal char, zigzag char releases greater heat than armchair char; moreover, zigzag char has a much lower activation energy than armchair char. CONCLUSION: In the simultaneous presence of CO and N 2 O, the char model prefers to adsorb N 2 O. The rate-limiting step of the two char models are located in different reaction stages, and CO mainly affects the N 2 O reduction stage. The presence of CO hinders the reduction of N 2 O on the surface of both zigzag and armchair char models. A rise of temperature can promote the reduction of N 2 O by char. Zigzag char is superior to armchair char in both thermodynamics and kinetics.

Background: Xyloglucan endotransglucosylase/hydrolases (XTHs) are a class of cell wall-associated enzymes involved in the construction and remodeling of cellulose/xyloglucan crosslinks. However, knowledge of this gene family in the model monocot Brachypodium distachyon is limited. Results: A total of 29 BdXTH genes were identified from the reference genome, and these were further divided into three main groups (Group I/II, Group III, and the Ancestral Group) through comparative phylogenetic analysis. Gene structure and protein motif analysis indicate that closely clustered BdXTH genes are relatively conserved within each group. A highly conserved amino acid domain (DEIDFEFLG) responsible for catalytic activity was identified in all BdXTH proteins. We detected three pairs of segmentally duplicated BdXTH genes and five groups of tandemly duplicated BdXTH genes, which have played important roles in the expansion of the BdXTH gene family. Cis -elements related to hormones, growth, and abiotic stress responses were identified in the promoters of each BdXTH gene. Most BdXTH genes have distinct expression patterns in different tissues and growth stages. Furthermore, when roots were treated with two abiotic stresses (salinity and drought) and four plant hormones (IAA, auxin; GA3, gibberellin; ABA, abscisic acid and BR, brassinolide), the expression levels of many BdXTH genes changed significantly, suggesting possible roles in response to various environmental stimuli and plant hormones. Conclusion: In this study, we performed genome-wide identification, characterization, and expression pattern analysis of the XTH gene family in Brachypodium, which provide valuable information for further elucidation of the biological functions of BdXTH genes in the model grass B. distachyon.