The Molecular Mechanism Of Betacene Synthesis Under High Nitrogen Stress In Suaeda Salsa L.

Liaohe Estuary is the most important estuarine wetlands in China.In recent years,the wetland area of Liaohe Estuary has deteriorated seriously owning to human factors and rapidly expanding economy.Suaeda salsa L.（Suaeda salsa）of Chenopodiaceae is a key plant in the ecological restoration of coastal wetlands.Nitrogen application has a good effect on the growth and soil nutrition improvement of Suaeda salsa.It is significant that betacene is osmotic regulation substances in Suaeda salsa,which can effectively improve the ability of plants to resist stress.Based on factors such as exogenous nitrogen input in Liaohe Estuary,this study selected Suaeda salsa as the test organism under high salinity in the field to explore t he effects of low（10 g N/m²）,medium（20 g N/m²）and high nitrogen（40 g N/m²）conditions on betacene synthesis of Suaeda salsa for 24 h.The contents of betacene,chlorophyll,malondialdehyde^[1]and hydrogen peroxide（H₂O₂）in Suaeda salsa were determined.They were explored the relationship between nitrogen sources and betaine accumulation,and use transcriptome technology to study the molecular mechanism of betaine synthesis in Suaeda salsa,and analyze the differentially expressed genes and signaling pathways.Specific research results are as follows:（1）The content of chlorophyll and betacene in Suaeda salsa increased with time under medium nitrogen condition,and a large amount of betacene and chlorophyll in Suaeda salsa were accumulated within 12 h.It is indicated that suitable nitrogen conditions could increase the contents of betacene and chlorophyll in Suaeda salsa.In addition,the betacene as a water-soluble nitrogen-containing pigment,when the nitrogen concentration increased,its content increased.（2）Under increasing in nitrogen application rate,the content of MDA and H₂O₂ in Suaeda salsa gradually decreased,indicating that nitrogen application can enhance the stress resistance of plant leaves,reduce the membrane lipid peroxidation,and effectively remove the reactive oxygen species produced by Suaeda salsa under salt stress.（3）According to GO enrichment analysis of differential genes,nitrogen application affected photosynthesis,plant hormone signal transduction,carbon metabolism,starch and sucrose metabolism and other metabolic pathways.The differences of genes in biological process,cell composition and molecular function were significant of different treatment time.（4）The KEGG enrichment analysis showed that the differential gene expression were mainly focused on photosynthesis,plant hormone signal transduction,carbon metabolism,starch and sucrose metabolism,and there were differentially expressed genes in tyrosine metabolism and beet pigment biosynthesis pathway.In addition,the effect of nitrogen source on the accumulation of betacene in the leaves of Suaeda salsa may be achieved by regulating the expression of 4,5-DOA dioxygenase gene.In summary,transcriptome techniques were used to analyze the effects of nitrogen application on the molecular mechanism of betacene synthesis,and it was found that the application of appropriate amount of nitrogen fertilizer was conducive to the accumulation of betacene pigment in Suaeda salsa,which provided a basic theoretical basis for further ecological restoration of Liaohe estuary wetland.