FIGURE 4 Heat map of
exogenous melatonin regulating the expression of OsGR3 ,OsGPX1 , OsNR2 , OsGS1 , and OsGOGAT1 in
seedlings under NaCl stress. (a) indicates the expression of theOsGR3 and OsGPX1 , (b) indicates the expression of theOsNR2 , OsGS1 and OsGOGAT1 .
3.5 | Expression regulation, GO annotation,
and KEGG metabolic pathway of exogenous melatonin for enzymes involved
in the AsA-GSH cycle and nitrogen metabolism in seedlings under NaCl
stress
GO functional annotations can be divided into three categories:
biological processes, molecular functions, and cell composition (Dong et
al.,
2021).
Based on the results of GO annotations and KEGG metabolic pathways of
rice OsGR3 , OsGPX1 , OsNR2 , OsGS1 , andOsGOGAT1 , these genes are involved in biological processes, such
as redox and cytosolic composition; functions, such as oxidoreductase
activity; and three metabolic pathways, including nitrogen metabolism,
alanine, aspartate and glutamate metabolism, and glutathione metabolism
(Figure 5a, b). Exogenous melatonin regulated gene expression in the
AsA-GSH cycle and nitrogen metabolism pathway in seedlings under NaCl
stress (Figure 6). NR reduces nitrate to nitrite, and then converts it
to ammonia, which is
converted under the action of GS and GOGAT for Gln and Glu. Further,
exogenous melatonin regulates the activities of NR, GS, and GOGAT by
upregulating the expression of OsNR2 , OsGS1 , andOsGOGAT1 , ultimately affecting the nitrogen metabolism whole
process. Glu can produce GS through the action ofglutamate cysteine
ligase (GCLM) and glutathione synthetase (GS II). In contrast, GSH can
synthesize Glu via γ-glutamyltranspeptidase (γ-GT), which connects the
AsA-GSH cycle with nitrogen metabolism, forming a complete metabolic
channel network (Fig. 6). Under the action of GR and GPX, a balance
between GSSG and GSH can be achieved, and the circulation and
regeneration of GSH can be promoted. Exogenous melatonin may upregulated
the expression of OsGR3 and OsGPX1 , therefore, upregulated
the activity of GR and GPX, and participated in the AsA cycle. The
purpose of the AsA-GSH cycle is to eliminate excessive ROS and reduce
the toxic effects of NaCl stress on seedlings.