Using Omics Analysis To Study The Mechanism Of Endogenous NO In The Clonal Plant Glechoma Longituba In Defensive Metabolism In Heterogeneous UV-B Environment

Clonal plants are distributed in almost all ecosystems.The clonal integration is very important for clonal plants' environmental adaptability.As an important environmental factor,ultraviolet-B(UV-B)has a significant effect on the growth and development of plants.Previous studies have shown that in heterogeneous UV-B radiation environment,NO played a role in regulating the clonal integration of defense materials but the pathway of endogenous NO production and its molecular mechanisms in response to UV-B stress are still not clear.Therefore,in this study we investigated the production pathway of endogenous NO in clonal plants under heterogeneous UV-B condition,and reveal the role of NO in the defense metabolic process of clonal plants with the omics analysis,for the purpose of understanding the mechanism of clonal plants in response to environmental stress.In this study,the ramets pair of clonal plant Glechoma longituba were growth in heterogeneous UV-B environment.The control group(A group),indirect UV-B radiated group(BI group)and direct UV-B radiated group(BII group)were compared with transcriptomics and metabolomics analysis.The main results are as follows:1.The analysis results of the endogenous NO synthesis pathway showed that the NO content in the leaves of the ramets in the heterogeneous radiation environment was significantly increased.The nitric oxide synthase(NOS)activity and carotenoid content had increased in the direct exposure to UV-B radiation's ramets(BII);however,the NOS?nitrate reductase(NR)activity?the content of nitrate and carotenoids had increased in ramets which without UV-B radiation(BI).2.The results of transcriptome analys is identified 27,582 differentially expressed genes between ramets of the control group(A)and heterogeneous UV-B radiation groups(BI,BII).These differential genes are mainly involved in plant biochemical processes,cellular components and molecular functions.Among them,most of the genes are involved in metabolic processes,followed by genes involved in catalytic activity,intracellular processes,integration,and single tissue processes.These differential genes were significantly enriched in 20 pathways,mainly including the biosynthesis of secondary metabolites,the metabolism of starch and sucrose,the biosynthesis of phenylalanine,carbon metabolism and so on.In addition,enrichment analysis of signal molecule synthesis-related pathways revealed that the genes expression of nitrogen metabolism(related to NO synthesis and regulation),arginine and proline synthesis metabolism were changed under heterogentous UV-B radiation condition.3.433 metabolites were detected with metabolomic analysis,amo ng them,29 differential metabolites were shared in A and BI groups,160 differential metabolites in A and BII groups,138 differential metabolites in BI and BII groups,and 18 differential metabolites in three groups.These metabolites are mainly flavonoids,terpenes,alkaloids and amino acids and their derivatives.These metabolites of the three groups are mainly enriched in the biosynthetic pathways of amino acids(such as phenylalanine biosynthesis,arginine and proline metabolic pathways,etc.)and fla vonoid and flavonol.The BII group owned the most amino acids and their derivatives,and group BI had the least.Moreover,there are the more flavonoid metabolites in BII group than A and BI groups.4.The conjoint analysis of differential genes and differential metabolites showed that trend of gene expression of C YP73 A,GOT1,hpp D,and PAL among the three groups were: BII>BI>A;MIF and aim E gene expression levels were: A>BI>BII;trans-cinnamic acids content was: BII>BI>A.The expression levels of arginine and proline metabolism-related GOT1 and P4 HA genes were: BII>BI>A;thats of MPAO,PAO1,NOA1 genes were: A>BI>BII.Furthermore,proline content trend was: BII>A,and BII>BI;that ofarginine content was: A>BII.In the flavonoid and the expression level of flavonol biosynthesis related E2.1.1.76 genes was: BII>A;CYP75A gene expression level was A>BI>BII.The content of apigenin and trihydroxyflavone were: BII>A,BII>BI;luteolin glucoside and glucoside tetrahydroxyflavone content were: A>BII;and kaempferol galactoside content was A>BII,BI>BII.Based on the above results,we believe that heterogeneous UV-B radiation induced a significant increase in NO content in the leaves of Glechoma longituba by activating the enzymatic pathway involving NOS and NR and the non-enzymatic pathway involving carotenoids and nitrite.The pathways of NO synthesis in the leaves of the ramets irradiated with(BII)and their connected ramets without UV-B(BI)were different.The increased NO in the leaves promoted the synthesis of proline and activates the phenylalanine metabolism pathway and further promoted the biosynthesis of flavonoids and flavonols,and finally activated the defensive metabolic reaction of Glechoma longituba.Moreover,with the interconnected stolons,the signals or substances between the ramets are integrated in the clonal network.Therefore,even clonal ramets that without UV-B radiation can induce a defensive response,which helped the pre-adaptation of the genet to the environment.The results of this study revealed the possible mechanism of the defense response of clonal plants in heterogeneous UV-B radiation environment,which is helpful understanding the environmental adaptability of clonal plants and their molecular mechanism.