The Mechanism Of Key Genes In Sucrose Metabolic Pathway Involved In The Leaf-head Formation In Brassica Rapa

Chinese Cabbage(Brassica rapa,2n=20,AA),as one of the important economically cultivated Brassica crops,belongs to the Cruciferae family with the characteristics of wide geographical distribution,rich morphological diversity.Sucrose metabolism including sugars synthesis,translocation,partitioning and utilization,is vital for growth and development of cabbage crops,such as the process of seed germination,flowering formation induced by vernalization,pollen development,leaf-head formation,as well as other key agricultural traits which relate to economic production and nutritional quality.Moreover,the soluble sugars formed by sucrose metabolism not only affect the cabbage taste but also improve the cold resistance of cabbage crops by changing sugars content and/or sugar singal.For example,a better taste for cabbage leaves by increasing the soluble sugar content and longer freshness for the detached pakchoi plants by slowing the degradation of sucrose and hexose consumption after an appropriate low temperature.Additionally,the intermediates from sugar metabolism are usually as precursors for other important components(such as precursors of glucosinolates)or linked with flavonoids involving in the nectar guide of cabbage flower to attract insects to pollinate.Furthermore,sucrose metabolism response to a variety of biotic and abiotic stresses to improve environmental adaptability through the formation of osmotic substance or sugar signals.The leafy-head formation of Chinese cabbage,since it has better edibility,storage and marketability,is often concerned as the primary agronomic trait by breeding workers.As so far,the research on the regulation mechanism of leaf-head formation has been carried out from different aspects ranging from histology,physiology,geometric structure,genetic law,plant hormones and light intensity,etc.Sucrose metabolism,although as the most basic metabolic pathway,involves the distribution of photosynthetic products in different leaves and cells in the early stage of head formation,causing uneven growth of leaves and promoting the leaf-head formation.The related molecular mechanism is not clear.Moreover,in recent years,the regulatory network involved in sucrose metabolism and its signal transduction pathway is complex and huge.The research on sucrose in cabbage crops mainly focuses on the measurement of related soluble sugars,and the analysis and excavation of its regulation network are rarely deep.Therefore,to understand the regulation mechanism of sucrose metabolism in Chinese cabbage to participate in the formation of leafy head,in this study,the sucrose metabolism key player of SWEETs,SUTs and INVs family genes which involved in sucrose transport,distribution and utilization were firstly analyzed by bioinformatics methods in the different plant taxa and cruciferous groups to explore its evolutionary footprint and functional differentiation.Secondly,the duplication patterns,sequence characteristics and expression pattern of SWEETs,SUTs and INVs family genes in the Chinese cabbage were analyzed to understand their basic information in the Chinese cabbage.Then,by combing RNA-Seq transcriptome with iTRAQ quantitative proteome technology,low-temperature-induced leafy-head formation for two phenotypes from an early stage of heading Chinese cabbage "chifu" was investigated.The key findings are as follows:1.The footprint and functional differentiation of SWEETs,SUTs and INVs in 92 sequenced genomes from different plant taxa were first investigated by homologous.Identification and phylogenetic relationship suggested that SWEETs with sucrose transport activity were originally from vascular plants,each SUT subclassifications had independent evolution patterns,and the newest CWINs subgroup of INVs originally appeared in gymnosperms plants.Further the footprint and phylogenetic relationship analysis for cruciferous genome-sequenced plants shown that gene members were differentially amplified for those three families but all conservative in Lineage I and part of the loss in Lineage III of Cruciferae family.Additionally,analysis for homologous identification,phylogenetic relationship,conserved domain and expression analysis in different tissues for BrSWEETs,BrSUTs,and BrINVs in triplicated B.rapa genome suggested that some of the retained members have missed part of domain or motif,and/or didn't check any expression in any tissues.In summary,the work reported here provides the groundwork for SWEETs,SUTs and INV in B.rapa crops,which will lead to a more detailed understanding for sucrose involved sugar translocation,partitioning and utilization involved plant growth and development,as well as a better adaptation for the environment,the trait for a global picture of the molecular dynamics.2.By combing RNA-Seq transcriptome with iTRAQ quantitative proteome technology,low-temperature-induced leafy-head formation for two phenotypes from an early stage of heading Chinese cabbage "chifu"was investigated A total of 2931 transcripts and 365 proteins were identified with significantly changed levels in abundance from heading and non-heading Chinese cabbage.The correlation analysis from transcripts to proteins suggested that rare genes related for all identified transcripts(R=0.1914)and quantitative proteins but reluctant good correlation for significantly different changed members(R=0.7179 for the members with same changing trend and R=0.5294 for members with the opposite changing trend)?KEGG functional shown that considerable numbers were enriched to the pathways of starch/sucrose metabolism and Glycolysis/Gluconeogenesis.And further analysis suggested that sucrose related genes of BrSWEET12-MF2,BRSWEET13-LF,BrSWEET14MF1,BrSWEET14-MF2,BrSWEET15-LF,BrSWEET15-MF1 and BrSWEET15-MF2may increase sugar accumulation by the hold-up of the phloem loading process.Besides,BrSWEET1-MF1,BrSWEET16-MF1,BrSWEET17-MFI andBrSWEETI 7-MF2,BrSUTILF,BrSUTl-LF,BrSUT9-LF,BrSUT9-MF1 from SUT family,BrCWIN2-MFl,BrCIN6LF,BrCWIN4-MF2,BrCWIN5-LFb,BrCWIN5-MF1,BrVIN1-MF2 from INV family may respond to the process of head formation for Chinse cabbage by involving in sucrose translocation and degradation.