Studies On Selection Of Pathenocarpic Fruit Inducers For ’Cuiguan’ Pear And Molecular Mechanism Of Gibberellin-Induced Parthenocarpy

Parthenocarpy refers to the development of a fruit without prior fertilization.Fruits thus produced are generally seedless,which has been recognized as a highly attractive agronomic trait.As one of the important temperate fruit trees,pears are widely cultivated throughout China.However,due to self-incompatibility,pollinizers and artificial pollination are indispensable to ensure the yield.Besides,pear blooms early and is vulnerable to the extreme weather in the spring,leading to poor fertilization and affecting volume.Previous studies have shown that exogenous plant hormones and plant growth regulators could effectively induce pear parthenocarpy.However,application of single plant hormones such as gibberellins could result in malformed fruit with persistent sepals,and affecting its marketability.Therefore,it is necessary to improve the ingredients of the original inducer or develop new inducers for parthenocarpic fruit.In addition,most of the current studies on artificial parthenocarpic fruit still focused on the physiological changes and molecular mechanisms during the process of young fruit enlargement,and few works have been done on the molecular mechanisms underlying early fruit-setting process.In this study,’Cuiguan’pear（Pyrus pyrifolia Nakai）,a leading cultivar in South China,was chosen to be the experimental material for us to study parthenocarpic effects of different inducers,to construct preliminary regulatory network of early fruit-setting,and to mine transcription factors involved in regulating early fruit-setting.The results are as follows:1)The combination of gibberellin and various ethylene inhibitors could reduce fruit shape index and fruit skewness.In addition,GA₄₊₇+Spd treatment could increase the content of soluble sugar content and soluble solid in mature parthenocarpic pears.Polyamines（putrosamine,spermidine）and Cu SO₄ treatments could successfully induce parthenocarpic fruit with deciduous calyxes.2)The early parthenocarpic fruit-setting regulatory network was constructed.The transcriptome analysis of GA₄₊₇-induced parthenocarpic’Cuiguan’pear was carried out,and the core genes of up-regulated modules at early fruit setting stage were screened and the regulatory network was preliminarily constructed.Transcriptome sequencing was performed on the young fruitlets of’Cuiguan’pears.A total of 219.8 Gb of original data were obtained,and the average mapping ratio to the reference genome of’Cuiguan’was as high as 87.76%.A total of 32512 genes were expressed,and 26108differentially expressed genes were obtained after filting.A total of 26 modules with different expression trends were obtained after WGCNA analysis,which were divided into two groups:GA-upregulated modules and CK（control）-upregulated modules.KEGG enrichment analysis showed that DEGs in GA-upregulated group mainly enriched in the process of genetic information transferring,RNA transport,proteasome process,TCA-cycle,amino acid biosynthesis and nitrogen metabolism.DEGs in the CK-upregulated modules are mainly enriched in the process of ubiquitination degradation,transcription,plasma membrane transport,and biosynthesis of various enzymes.A regulatory network for early fruit-setting of‘Cuiguan’pear based on GO enrichment pathway was preliminarily constructed and hub genes in up-regulated modules were selected.3)Hub transcription factors regulating parthenocarpic fruit setting were selected.A total of 2005differentially expressed transcription factors were identified,among which the transcription factor families with the largest number of members were AP2/ERF,MYB,BHLH,NAC and C2H2.The number of significantly over-expressed TF families reached the maximum on CK14.We have identified 10 fruit-setting associated pathways including plant hormone synthesis and signal transduction,cell cycle and cell expansion,cell wall biosynthesis and modification,photosynthesis and carbohydrate biosynthesis and transport.Genes in these pathways were used as baits to identify key TFs regulating fruit setting process via correlation analysis.Finally,the net work was constructed by WGCNA,the connection of TFs and target fruit-setting associated pathways were preliminarily confirmed.