Preliminary Study Of Gene Families And Metabolic Pathways Related To Nitrogen Utilization In Cucumber

Cucumber,one of the main vegetables cultivated in facilities,is a shallow root crop with a relatively poor ability to absorb fertilizers and water,and its growth and development strongly depend on the nitrogen supply.In agricultural production,a large amount of nitrogen fertilizer was applied to increase crop yields.However,excessive application of nitrogen fertilizer usually showed negative effects on cucumber quality and resulted in a series of environmental pollution problems.Therefore,it is very important to improve the nitrogen utilization efficiency of cucumber.Nitrate transporter 1/peptide transporter family(NPF),amino acid transporters(AAT),ammonium transporters(AMT)and nitrogen assimilation related genes(NAG)were widely involved in plant nitrogen metabolism and were able to regulate nitrogen transport and distribution in plants.However,genes related to nitrogen utilization in cucumber have not been fully identified.In this paper,on a basis of systematic identification and analysis of genes related to nitrogen utilization in cucumber,the tissuespecific expression patterns of NPF,AMT,AAT and NAG genes in cucumber plants under different nitrogen conditions were investigated by transcriptome sequencing and qRT-PCR assay.Finally,the functions of these genes and the law of nitrogen metabolism and transport in cucumber were preliminarily analyzed combined with the determination of nitrogen compounds in different tissues of cucumber plants.The finding will provide clues for the comprehensive analysis of cucumber nitrogen absorption,assimilation and transport pathways,as well as provide a basis for improving the nitrogen utilization efficiency of cucumber plant.The main results are as follows:1.A total number of 54 CsNPF genes were identified from cucumber genome.Tissue expression analysis revealed that CsNPF6.4 specifically expressed in roots,CsNPF6.3 exhibited a high expression in petioles,and CsNPF2.8 was highly expressed in fruits.According to the function of homologous genes in Arabidopsis,CsNPF6.4 may be responsible for the absorption of NO3-in roots,CsNPF6.3 may be involved in the storage of NO3-in petiole,and CsNPF2.8 may promote NO3-transport to the embryos.2.There were 8 CsAMT genes in cucumber genome.Tissue expression analysis showed that CsAMT1.1 was highly expressed in old leaves of cucumber,CsAMT1.4 exhibited higher expression level in roots,and CsAMT1.5 was highly expressed in male buds.According to the function of homologous genes in Arabidopsis,CsAMT1.1 could mediate the transport of NH4+in senescent leaves,CsAMT1.4 may be involved in the absorption of NH4+ by plant roots,and CsAMT1.5 may promote nitrogen transport to developing flowers.3.Cucumber genome contained 55 CsAAT genes.The expression profiles obtained from different tissues demonstrated that CsAAP3 and CsAAP4 were highly expressed in cucumber roots and stems,the transcription level of CsLHT7 was up-regulated in roots,CsLHT5 was highly expressed in female flowers,and CsLHT2 was specifically expressed in male buds.According to the function of homologous genes in Arabidopsis,CsAAP3 and CsAAP4 may be involved in the absorption of amino acids in root phloem and the transport of amino acids from xylem to phloem in stems,CsLHT7 may be responsible for the absorption of amino acids in roots,CsLHT5 might regulate floral organ development and fertilization,and CsLHT2 may promote the development of male buds.4.In cucumber genome,identified 18 CsNAGs was encoded the enzymes involved in nitrogen assimilation.Tissue expression analysis were performed and found that CsNIA1 was highly expressed in roots,CsNIA2 and CsNIA3 were specifically expressed in young leaves,and CsGLN2 and CsGLU1 displayed up-regulated expression in leaves.According to the function of homologous genes in Arabidopsis,CsNIA1 may be responsible for nitrate reduction in roots,CsNIA2 and CsNIA3 may be responsible for nitrate reduction in young leaves,and CsGLN2 and CsGLU1 may be mainly responsible for nitrogen assimilation in leaves.5.Amino acids were the major form of nitrogen transport in cucumber plants.Nitrate nitrogen was mainly assimilated in the root,and nitrogen in cucumber root were transported to the shoot in the form of amino acids and nitrate nitrogen.The form of nitrogen that mainly transported to the fruit was amino acids in the cucumber plant.qRT-PCR analysis further verified the function of nitrogen utilization related genes in different tissues.