Central metabolism produces carbohydrates and amino acids that are tightly correlated to plant growth and thereby crop productivity.Malate is reported to link mitochondrial respiratory metabolism with cytosolic biosyn...Central metabolism produces carbohydrates and amino acids that are tightly correlated to plant growth and thereby crop productivity.Malate is reported to link mitochondrial respiratory metabolism with cytosolic biosynthetic pathways.Although the function of malate metabolism-related enzymes in providing carbon has been characterized in some plants,evidence for this role in the fleshy fruit of cucumber is lacking.Here,radiolabeled bicarbonate fed into the xylem stream from the cucumber roots was incorporated into amino acids,soluble sugars,and organic acids in the exocarp and vasculature of fruits.The activities of decarboxylases,especially decarboxylation from NADP-dependent malic enzyme(NADP-ME),were higher in cucumber fruit than in the leaf lamina.Histochemical localization revealed that CsNADP-ME2 was mainly located in the exocarp and vascular bundle system of fruit.Radiotracer and gas-exchange analysis indicated that overexpression of CsNADP-ME2 could promote carbon flux into soluble sugars and starch in fruits.Further studies combined with metabolic profiling revealed that the downregulation of CsNADP-ME2 in RNA interference(RNAi)lines caused the accumulation of its substrate,malate,in the exocarp.In addition to inhibition of glycolysis-related gene expression and reduction of the activities of the corresponding enzymes,increased amino acid synthesis and decreased sugar abundance were also observed in these lines.The opposite effect was found in CsNADP-ME2-overexpressing lines,suggesting that there may be a continuous bottom-up feedback regulation of glycolysis in cucumber fruits.Overall,our studies indicate that CsNADP-ME2 may play potential roles in both central carbon reactions and amino acid metabolism in cucumber fruits.展开更多
基金This work was supported by the National Natural Science Foundation of China(32272695 and 31972398 to X.S.)the National Key Research and Development Program of China(2019YFD1000300)+3 种基金the National Natural Science Foundation of China(31960591 to N.S.)the Max-Planck Society and European Union’s Horizon 2020 research and innovation programme,project PlantaSYST(SGA-CSA No.664621 and No.739582 under FPA No.664620)the China Agriculture Research System of MOF and MARA(CARS-23)the 111 Project of Ministry of Education of P.R.C.(B17043).
文摘Central metabolism produces carbohydrates and amino acids that are tightly correlated to plant growth and thereby crop productivity.Malate is reported to link mitochondrial respiratory metabolism with cytosolic biosynthetic pathways.Although the function of malate metabolism-related enzymes in providing carbon has been characterized in some plants,evidence for this role in the fleshy fruit of cucumber is lacking.Here,radiolabeled bicarbonate fed into the xylem stream from the cucumber roots was incorporated into amino acids,soluble sugars,and organic acids in the exocarp and vasculature of fruits.The activities of decarboxylases,especially decarboxylation from NADP-dependent malic enzyme(NADP-ME),were higher in cucumber fruit than in the leaf lamina.Histochemical localization revealed that CsNADP-ME2 was mainly located in the exocarp and vascular bundle system of fruit.Radiotracer and gas-exchange analysis indicated that overexpression of CsNADP-ME2 could promote carbon flux into soluble sugars and starch in fruits.Further studies combined with metabolic profiling revealed that the downregulation of CsNADP-ME2 in RNA interference(RNAi)lines caused the accumulation of its substrate,malate,in the exocarp.In addition to inhibition of glycolysis-related gene expression and reduction of the activities of the corresponding enzymes,increased amino acid synthesis and decreased sugar abundance were also observed in these lines.The opposite effect was found in CsNADP-ME2-overexpressing lines,suggesting that there may be a continuous bottom-up feedback regulation of glycolysis in cucumber fruits.Overall,our studies indicate that CsNADP-ME2 may play potential roles in both central carbon reactions and amino acid metabolism in cucumber fruits.
