Accumulation And Distribution Characteristics And Transport Mechanism Of Photosynthetic Products In Camellia Oleifera

Camellia oleifera is a unique woody oil tree species in south of China.It has high economic value,strong adaptability,wide application and great potential for comprehensive development and utilization.China actively develops the camellia oil industry,which is of great significance to ensuring the safety of grain and oil,easing the pressure of cultivated land,and increasing farmers’income.Improving the output and quality of Camellia oleifera has become one of the key scientific problems to be solved urgently.Therefore,it is of great scientific value and theoretical significance to elucidate the distribution,transport and storage characteristics of photosynthetic products of Camellia oleifera,study the differential factors,and screen the key genes and functions.In this paper,the characteristics of photosynthetic product accumulation and distribution of Cen Ruan No.3 and Xiang Lin 210 were studied by ¹³C isotope labelling.Transcriptome sequencing technology was used to obtain sucrose transporter genes and verify their functions,to interpret and regulate photosynthetic product distribution and transport mechanism,which can provide theoretical basis for the regulation of Camellia oleifera source reservoir,and provide technical support for the improvement of Camellia oleifera yield and quality.The main research results are as follows:（1）Photosynthetic parameter:The light saturation point（LSP）of Xiang Lin 210 was275.02μmol·m^-2·s^-1;Cen Ruan No.3 was 263.20μmol·m^-2·s^-1.The light compensation point（LCP）of Xiang Lin 210 was 29.11μmol·m^-2·s^-1;Cen Ruan No.3 was 26.51μmol·m^-2·s^-1.The maximum net photosynthetic rate(P_nmax)of Xiang Lin 210 was 10.80μmol·m^-2·s^-1.Cen Ruan No.3 was 14.09μmol·m^-2·s^-1.The maximum net photosynthetic rate of Cen Ruan No.3 and Xiang Lin 210 in each period was measured.During the whole fruit development period,the maximum net photosynthetic rate increased first and then decreased.The maximum values of the two varieties both reached in July,which were 10.08μmol·m^-2·s^-1and 14.09μmol·m^-2·s^-1;The lowest values appeared in June,6.57μmol·m^-2·s^-1 and 6.22μmol·m^-2·s^-1.（2）Transport characteristics of photosynthate:the leaves were fed with carbon isotopes in June,as time changes,the isotopic abundance of the marked leaves decreased gradually in Cen Ruan No.3 and reached the lowest value after 48 h（1.0794%）;the lowest branches of isotope abundance gradually rise and reached the maximum in 72 h（1.0914%）;the change of fruit abundance was consistent with that of the branches and fruit abundance peaked at 72 h（1.0823%）.The isotope abundance of the marked leaves and branches of Xiang Lin 210 increased first and then decreased,while the isotope abundance of the fruit increased slowly and reached the maximum value at 72 h（1.0866%）.（3）Accumulation of photosynthetic products:after carbon isotope feeding and sampling in June,July,September and Octobe.With the development and maturity of fruits,the isotope abundance of Cen Ruan No.3 marker leaves gradually increased,reaching the maximum in October;while that of Xiang Lin 210 marker leaves reached the maximum in September,and the abundance decreased slightly in October.The isotopic abundance of Cen Ruan No.3 branch decreased first and then increased,and reached the minimum value in September（1.0818%）.The variation trend of branch abundance of Xian Lin 210 was basically consistent with Cen Ruan No.3,but reached the minimum value in July（1.0824%）.The variation trend of Cen Ruan No.3 and Xiang Lin 210 fruit abundance was basically the same,both of which increased first,then decreased and then slightly increased.The minimum values of the two varieties appeared in June,which were 1.0823%and 1.0866%respectively.The maximum value appeared in July,which were 1.0892%and1.0909%respectively.（4）Change characteristics of soluble sugar content:in Cen Ruan No.3 and Xiang Lin210,the changes of soluble sugar content in the leaves increased first and then decreased,and finally leveled off,and reached the maximum value in July.The soluble sugar content of fruit increased first,then decreased,then increased slightly,and reached the maximum value in July.（5）Transcriptome gene assembly and functional interpretation:a total of 54,217unigene sequences were obtained by sequencing Cen Ruan No.3 and Xiang Lin 210transcriptome.After sample correlation test,most of the correlations in biological repeats were above 0.8.After comparing each unigene sequence in the public database,a total of43,998 unigene sequences could match the known genes in the public database,accounting for 81.15%of all non-redundant genes.By comparison in COG database,a total of 18,600unigene genes have homology with genes in COG database,which can be divided into 25categories according to their functions.After comparing with the GO database,a total of138,546 GO function comments were obtained,which can be divided into 3 categories and50 subcategories.In the KEGG database comparison,16,798 unigene were involved in 130known metabolic or signaling pathways.（6）Screening of differentially expressed genes:by analyzing the differentially expressed genes of Cen Ruan No.3 and Xiang Lin 210 in different periods,the number of differentially expressed genes in June was huge compared with that in other three periods,Among them,Cen Ruan No.3 has a maximum of 11,182,and Xiang Lin 210 has a maximum of 1,1179.However,there were relatively few differentially expressed genes in July,September and October.The lowest number of Cen Ruan No.3 is 152,and the lowest number of xiang Lin 210 is 269.With the development of fruit,the related genes of starch synthase,fructokinase and sucrose synthase were up-regulated,while amylase and phosphorylase were down-regulated.The synthesis of fat is transformed by starch metabolism,and the oil of Camellia oleifera fruit is mainly transformed at the later stage.The up-regulation and down-regulation of related enzyme genes are consistent with the development process of fruit.Through further analysis and screening,7 sucrose transporter-related genes were obtained,namely,SUC1-like、SUC2-1、SUC2-2、SUC2-3、SUC2-4、SUC2-like and SUC4.