Legume Genomics and Genetics 2025, Vol.16, No.5, 225-233 http://cropscipublisher.com/index.php/lgg 228 Figure 1 Alterations of H3K4me3 in nitrogen and carbon metabolic pathway between nodules and remaining roots. Heatmaps show fold change of expression and H3K4me3 level in genes along ureide and purine biosynthesis pathway between nodules and remaining roots. Red color indicates higher level while blue color indicates lower level in nodules. 2-OG, 2-oxoglutarate; Gln, Glutamine; Glu, Glutamate; GOGAT, Glutamate synthetase; GS, Glutamine synthetase; NH4+, Ammonium; R5P, Ribose 5-phosphate; PRS, Phosphoribosylpyrophosphate synthetase; PRPP, 5-phosphoribosy1-1-pyrophosphate; PPAT, Glutamine phosphoribosyldiphosphate amidotransferase; RRA, 5-phosphoribosylamine; GARS, GAR synthetase; GAR, 5-phosphoribosylglycinamide; GART, GAR transfromylase; FGAR, 5-phosphoribosyl-N-formylglycinamide; FGAMS, FGAM synthetase; FGAM, 5-phosphoribosyl-N-formylglycinamidine; AIRS, AIR synthetase; AIR, 5-phosphoribosylaminoimidazole; AIRC, AIR carboxylase; CAIR, 1-(5-phosphoribosyl)-5-amino-4-carboxyimidazole; SAICARS, SAICAR synthase; SAICAR, 1-(5-phosphoribosyl)-4-(N-succinocarboxamide)-5-aminoimidazole; ADSL, adenylosuccinate lyase; AICAR, 1-(5-phosphoribosyl)-5-amino-4-imidazolecarboxamide; AICART/IMPC, AICAR transformylase/IMP cyclohydrolase; IMP, inosine monophosphate; IMPD, IMP dehydrogenase; XMP, Xanthosine monophosphate; 5NT, 5′-nucleotidase; PNP, purine-nucleoside phosphorylase; NSH2, nucleoside hydrolase 2; XA, xanthine; XDH, Xanthine dehydrogenase; UA, uric acid; UO, urate oxidase(uricase); 5HTP, 5-hydroxyisouratre; HIUH, hydroxyisourate hydrolase; OHCU, 2-oxo-4-hydroxy-4-carboxy-5-ureidoimidazoline decarboxylase; OHCUD, OHCU decarboxylase; AT, allantoinase; Suc, Sucrose; SS, Sucrose synthase; AI, Alkaline invertase; Fru, Fructose; HK, hexokinase; FK, fructokinase; G6P, glucose-6-phosphate; PGI, glucose-6-phosphate isomerase; F6P, fructose-6-phosphate; PFK, 6-phosphofructokinase phosphohexokinase; F1,6BP, fructose 1,6-bisphosphate; Aldo, aldolase; GADP, glyceraldehyde 3-phosphate; TPI, triosephosophate; DHAP, dihydroxyacetone phosphate; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; 1,3BPG, 1,3-bisphosphoglyceric acid; PGK, phosphoglycerate kinase; 3PG, 3-phosphoglycerate; PGM, 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase; 2PG, 2-phosphoglycerate; Enol, enolase; PEP, phosphoenolpyruvate; PEPC, PEP carboxylase; OAA, Oxaloacetate; MDH, malate dehydrogenase. N = nodules, RR = remaining roots (Adopted from Wang et al., 2020) 4.3 Epigenetic feedback loops and hormonal interplay Epigenetic regulation alone is not enough; the intervention of plant hormones should not be ignored either. During the development of root nodules, there is a rather special regulatory mode-epigenetic feedback circuits, which link several mechanisms including DNA methylation, histone modification and chromatin remodeling together (Davalos and Esteller, 2022). These circuits can act as a "stabilizer", keeping gene expression in a relatively fixed state and preventing it from fluctuating excessively with environmental changes. However, things are often not that absolute. When developmental signals or hormone gradients change, such as fluctuations in auxin or cytokinin levels, these feedback loops will also respond. They may readjust their state by regulating the activity of chromatin modification enzymes, allowing external signals to eventually be stably "translated" into the occurrence
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