Transcriptome Analysis-based Study On Molecular Mechanism Of Gibberellin-Induced Parthenocarpy In ’Cuiguan’ Pear

Due to natural cross-pollination,and the gametophyte self-incompatibility,a certain number of pollination trees or pollination branches should be set up during pear production in order to ensure the yield.When the fruit trees encounter extreme weather such as frost,low temperature and increased spring rainfall,the pollination and pollen vigor will be affected,resulting in a decrease in fruit yield due to poor fertilization.Artificial induction of parthenocarpy by exogenous gibberellin,auxin,and cytokinin growth regulators can reduce losses and increase fruit set rate.It is important to study the molecular mechanism of fruit set,as it can provide theoretical basis for the development of parthenocarpy inducer formulation and parthenocarpy molecular breeding.In this study,’Cuiguan’,which is widely cultivated in southern China,was used as the experimental material.Based on the previous research of our lab,the effect of gibberellin-induced parthenocarpy was verified.The gibberellin-induced parthenocarpic and water-treatment control fruitlets at different developmental stages were selected for phytohormone content measurement,cytological observation and transcriptional pattern analysis.The molecular mechanism of parthenocarpy was explored from the metabolic and transcriptional levels in this study.The main results are as follows:1.Appication of GA3.GA4+7 and GA4+7+NAA at anthesis can induce parthenocarpy in’Cuiguan’pear,while ethylene inhibitors 1-MCP.,PZA and ATA showed no effects on induce inducing parthenocarpy.Compared with GA4+7 treatment,GA3 or GA4+7+NAA can improve fruit appearance quality by reducing fruit shape index and fruit fruit shape skewness to a certain extent,and improve the internal quality of the fruit by increasing fruit edible rate,soluble solids and soluble sugar content.,reducing fruit organic acid content.2.The content of gibberellin and auxin increased in gibberellin-induced parthenocarpic fruitet,while abscisic acid and ethylene synthesis were inhibited.In addition,the single fruit weight,horizontal and vertical diameter,cell diameter and cell layer of gibberellin-induced parthenocarpic fruitlets were significantly higher than those of control.It indicated that gibberellin treatment can maintain the division and enlargement of cells in the ovary by regulating the homeostasis of gibberellin,auxin,abscisic acid and ethylene,so that fruit setting can be induced without pollination.3.In total.219.8 Gb data were generated from 33 transcriptome sequencing libraries.And about 70%reads could be mapped to the reference genome、a total of 38,788 enes were detected,and 4.378 transcrips were predicted as new genes.There are 14284 genes differentially expressed in gibberellin-induced parthenocarpic fruitlets,including 1040 transcription factor encoding genes.The differentially expressed phytohormone metabolism,transport,signal transduction related genes and core cell cycle and expansins gene family genes were identified,and they have similar trends with related phenotypes.It indicated that gibberellin can regulate fruit set by regulating the metabolism,polar transport.signal transduction process of different plant hormones,and cell division and cell expansion.After screening by clustering parameters min.std>0.1,member.ship>0.5,9933 differentially expressed genes were divided into 5 groups according to the expression patterns.The results of KEGG enrichment analysis showed that genes of photosynthesis,plant hormone signal transduction,carbohydrate metabolism,and secondary metabolite biosynthesis pathways were involved in the parthenocarpy process.4.Based on cluster analysis and weighted gene co-expression network analysis.we found 2791 candidate positive regulatory genes in gibberellin-induced parthenocarpy.Functional verification of some candidate genes has demonstrated a possible network of parthenocarpic transcriptional regulation:Gibberellin may regulate metabolism and signal transduction processes by regulating other plant hormones such as ethylene,auxin,etc.The expression of downstream structural genes may be activated or inhibited by transcription factors such as MADS-box,etc.,thereby inducing parthenocarpy.