The Omics Study On Sink-source Regulation Pathway In Leaves Of Populus×Xiaohei T.S. Hwang Et Liang Cutting Seedlings And Its Nitrogen Starvation Conditions

During the process of plant leaf sink-source conversion,its sink-source regulation pathway is very important for plants to obtain high yield and good quality.In addition,nitrogen also plays an important role in leaf sink-source regulation pathway.In this study,three weeks old Populus×xiaohei T.S.Hwang et Liang cutting seedlings were treated with 1 mmol·L^-1NH₄NO₃（control group）and 0 mmol·L^-1 NH₄NO₃（treatment group）respectively.At the same time,the physiological indexes related to sink-source of plant leaves were measured and cluster analysis was carried out to determine the period and specific position of Populus×xiaohei T.S.Hwang et Liang leaves from sink leaf development to sink-source transition leaf.The molecular mechanism of sink-source regulation pathway in sink leaf,sink source transition leaf and source leaf and the effect of N on regulation pathway were analyzed by omics method combined with the changes of growth and physiological indexes.The research results are as follows:（1）The morphology,biomass,photosynthetic parameters,chlorophyll content,chlorophyll fluorescence parameters and other indicators of plant sink leaf（leaf 1）in the treatment group and the control group were measured according to the time sequence of leaf development（every three days）.Through cluster analysis,the results showed that 1 leaf（sink leaf）of seedlings in the two groups developed to the stage of sink-source transition leaf on the 9th day.Through further analysis,it is determined that the hub indicators of the process are:P_n,C_i,ФPSⅡ,ETR,N and MC.（2）The biomass,photosynthetic parameters,total phenol content,nitrogen metabolizing enzymes and carbohydrate metabolizing enzymes of the leaves in each leaf sequence of the two groups of seedlings cultivated to the 9th day were measured.The results of cluster analysis showed that in the two groups of seedlings,the leaves with leaf rank 5 were in the position of performing the function of sink-source transition leaves,which was consistent with the position of sink-source transition leaves determined by the time sequence of leaf development.The study on the physiological function of leaves in each leaf rank of seedling plant shows that its hub functional indexes are GS、C_i、G_s、T_r、MDA、CAT、POD、LA、Fru、TP、Y（NPQ）and Y（NO）.（3）miRNA analysis showed that UGD5（potri.010g159800）in the sink leaf specific module（turquoise module）and UGD4（potri.017g092000,potri.004g118600）in the sink-source transition leaf specific module（yellow module）regulated by Novel＿104 were differentially expressed in metabolic pathway of starch and sucrose metabolism.Hub genes analysis identified 26 highly associated hub genes.These hub genes are closely related to photo-assimilation,starch metabolism,sucrose metabolism and photorespiration in sink-source regulation pathway.The results of transcription factor analysis showed that the differentially expressed transcription factors in the sink leaf specific module（turquoise module）were significantly enriched in the protein ubiquitination pathway,and the differentially expressed transcription factors in the sink-source transition leaf specific module（yellow module）were significantly enriched in starch metabolism and sucrose metabolism.In the source leaf specific module（blue module）,the differentially expressed transcription factors were mainly enriched in leaf senescence and nitrogen compound transport.（4）miRNA analysis showed that the target genes of differentially expressed miRNAs were mainly concentrated in biological processes such as pigment synthesis and metabolism,biosynthesis and secondary metabolite biosynthesis under nitrogen starvation.Hub genes analysis identified 17 highly associated hub genes under nitrogen starvation.These hub genes are closely related to carbon and nitrogen transport,proteolysis,protein ubiquitination and xylem development.Under nitrogen starvation,the differentially expressed transcription factors in sink leaf were significantly enriched in leaf senescence.The differentially expressed transcription factors in sink-source transition leaf were significantly enriched in the regulation of protein hydrolysis,nitrogen compound transport,carbohydrate transport,starch metabolism and sucrose metabolism.The differentially expressed transcription factors in the source leaf were significantly enriched in carbohydrate transport and starch metabolism.In conclusion,it is the first attempt to determine the time from the development of sink leaf to the sink-source transition leaf and the location of the plant by using the physiological indicators related to sink and source from the two dimensions of time and space.To screen the highly correlated hub genes in the regulation pathway of sink-source and under the condition of nitrogen starvation.It provides gene resources for coordinating the sink and source between leaves through sink-source regulation,so as to finally improve the biomass of poplar.