| The tree peony(Paeonia suffruticosa)is a worldwide well-known ornamental flower,however,it is couldn't be live for long in pot cultivation.Which is an obstracle in the tree peony industial seedlings.To broaden the cultivation scope of tree peony,the morphological indexes of potted peony,the rule of soluble sugar content in different development stages,the sucrose transporting pathway,some key genes such as sucrose transporter genes(Ps SUT2)were studied with Paeonia suffruticosa ‘Luo Yanghong' as the scions,and Paeonia ostii and Paeonia broteri as stocks,separately.The paper provides theory and technology support in molecular breeding and genetic improvement of the tree peony.The main results were as follows:1.The morphological indexesThere were no significant differences in the indexes such as the plant height,the crown wide of the two kinds of tree peony in the annual growth period.,however,In Paeonia suffruticosa ‘Luo Yanghong' grafted in Paeonia broteri,the annual branch length,the bud number,bud height,bud diameter were all bigger than Paeonia suffruticosa ‘Luo Yanghong' grafted in Paeonia osti.,and the differences were significant.The Paeonia broteri is a better material as stock of potted peony.2.The soluble sugar contentThe leaf sucrose content of Paeonia suffruticosa ‘Luo Yanghong' grafted in Paeonia ostii was higher than the one grafted in Paeonia broteri in the annual growth period(exclusion of summer dormancy stage).These results indicated of small bud number and the weaker sink strength in the peony in Paeonia ostii.And also,it was root provided carbon source material for bud development in the tree peony.Leaf stipe was a main channel for sucrose transportation,and sometimes it could be used to store the sucrose temporarily.The post-anthesis stage is crucial for the sucrose accumulation and metabolism in bud,so increase of P,K fertilizer is beneficial to the bud development.Root and stem were the main organs for sucrose storage in the winter dormancy stage.Stem showed more capable on the sucrose storage in the peony grafted in Paeonia ostii,while root more capable in the peony grafted in Paeonia broteri.When the tree peony was germinant,the sucrose content continuously decreased in the grafted Paeonia broteri root,we speculate that it provides carbohydrate for bud developement.In the growth stage after autumn,Paeonia suffruticosa ‘Luo Yanghong' grafted in Paeonia broteri was still vigorous in the leaves,stipes and buds compared with the one grafted in Paeonia ostii.The prolong of the growth stage after autumn help the leaves of the peony grafted in Paeonia broteri compound more sucrose transporting to the root,and it is the reason why peony grafted in Paeonia broteri breeds more buds.3.The sucrose transporting pathwayThe results showed that the CF was confined in the phloem cells,and the SE/CC was isolated to the PP in the main vein of the leaf in the growth stage and before the dormancy stage.while the CF was diffused in the stipe,the current stem,the perennial stem and the root in spite of the different signal intensity.It was considered that the symplasmic unloading pathway of the sucroseexist in the transport phloem cells including the stipe,the current stem,the perennial stem and the root.There was no significant difference in the Paeonia suffruticosa ‘Luo Yanghong' grafted together with the two kinds of stock.According to the ultrastructure of phloem and its surrounding parenchyma cells in the main vein of the leaf,the stipe,the petal,the root in the growth stage,the grafted location before the winter dormancy stage,the grafted Paeonia ostii root before the winter dormancy stage,the SE/CC complex and their surrounding PP cells have seldom plasmodesmata,and at the same time,there were paramural body,vesicles,cell wall ingrowth of SE and CC,the intercellular space was bigger between the PP cells and the vesicles in them.As a result,the apoplasmic unloading pathways exist mainly between them.The symplasmic unloading in the grafted Paeonia broteri root may prompt the sucrose backflow to the root.4.The cloning and expression analysis of sucrose transporter gene Ps SUT2Sucrose transporter genes was cloned from the leaves of Paeonia suffruticosa ‘Luo Yanghong' by RACE technique,named Ps SUT2,accession number was KC542396 in the Gen Bank.The full length c DNA of Ps SUT2 was 2 347 bp,encoding a protein of 601 amino acids.Its molecular mass is 64.6 KD,and p I is 6.14.The identities of putative amino acid sequence of Ps SUT2 compared with that of SUT gene from Vitis vinifera is 75.27%.Ps SUT2 protein contains twelve transmembrane helical structures,which belongs to the major facilitator superfamily.Expression of Ps SUT2 gene in different organs were performed with RT-q PCR at the different developmental stage of Paeonia suffruticosa ‘Luo Yanghong' grafted in the two kinds of stocks.The main results showed that the profile of Ps SUT2 gene was similar in the two kinds of stock,and Ps SUT2 expressed mainly in the leaf,the stipe,the bud,the current stem,the perennial stem,petal and the root in the autumn growth stage.5.Mining of key genes involving in sucrose transporting and metabolizing pathway in Paeonia suffruticosa ‘Luo Yanghong' by RNA-seq.The transcriptome of Paeonia suffruticosa ‘Luo Yanghong' petals in small bell stage and flowering stage were studied by RNA-seq.De novo assemblies yielded 59 616 unigenes and 33919 unigenes were annotated.There were 4 324 differentially expressed genes in flowering,the number of up-regulated genes and down-regulated genes were 1 886 and 2 338 respectively.KEGG pathway enrichment analysis of differentially expressed genes showed that there were 118 pathways enriched,the carbon metabolism and starch and the sucrose metabolism were the important pathways.The genes which significantly differentially expressed in these pathways may playe an important role in the regulation of Paeonia suffruticosa ‘Luo Yanghong' response to flower.Ps SUT1 gene was up-regulated in the SUT family,and 8 new members(SWEET)for sucrose transporting in the Paeonia suffruticosa ‘Luo Yanghong' were founded(3 up-regulated and 5 down-regulated).8 sucrose metabolism enzyme genes differentially expressed,Inv genes 4(2 up-regulated and 2 down-regulated),SS genes 4(all up-regulated),while SPS genes and Ps SUT2 were not differentially expressed.We speculate that these 17 differentially expressed genes may play an important part in the sucrose transportation and metabolism during the flowering of Paeonia suffruticosa ‘Luo Yanghong'. |
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