Integrative Analysis Of Mango Floral Induction By SPD Through Metabolomicand Transcriptome

Mango(Mangifera indica L.)is an important tropical economic fruit tree in China.At present,more than 50% of main mango producing areas in China often use soil spraying with paclobutrazol to control shoots and promote flowers.However,long-term use of PBZ or improper control of the amount of PBZ in soil will easily lead to soil residue and decline of tree potential,which will affect the yield and fruit quality.Therefore,it is a difficult problem for mango industry to select green low-residue flower regulator.Previous studies found that foliar spraying of mepiquat chloride and uniconazole(SPD)with appropriate concentration can significantly promote the flowering rate of mango,and it is safe and low in residue.However,the mechanism of regulating flowering of mango fruit is still unclear.Therefore,studying the key regulation ways and regulation factors of mango flowering in response to SPD treatment can lay a theoretical foundation for analyzing the regulation network of mango flowering in response to SPD treatment,and is of great significance for guiding the green and efficient production of mango and understanding the regulation theory of mango flowering.In this study,mango ’Tainong No.1’ was used as the experimental material,and the effect of exogenous SPD treatment on flowering of mango was clarified.The critical period of SPD promoting flowering of mango was observed by paraffin section,and the transcriptome and metabolomic maps of terminal buds at different stages after SPD treatment and clean water control treatment were further constructed,and the key regulatory ways and ways of responding to SPD treatment to promote flowering of mango were identified.The main results are as follows:(1)The effect of SPD on flowering of mango fruit and the period of flower bud differentiation were clarified.The flowering rate and single plant yield of mango trees sprayed with SPD for two consecutive years were significantly higher than those of the control,and the flowering rate exceeded 80% in both years,which proved that SPD was effective in promoting mango flowering.Morphological and cytological observations were made on the tip of the sp D-treated group and the control group at different stages(30,60,80 and 100d)after treatment.It was found that the external and internal morphological characteristics of the terminal bud changed significantly at80 days after SPD treatment compared with the control group,which showed swelling and lateral expansion of the shoot tip and loss of its dome shape.Therefore,it is speculated that 80 d after treatment is the key period for SPD to promote flower bud formation of mango fruits.(2)Transcriptome maps of terminal buds at different development stages after SPD treatment and control treatment were constructed.Transcriptome sequencing was carried out on the terminal bud samples of SPD treatment group(TA,TB,TC,TD)and control group(A,B,C,D)after 30,60,80 and 100 d days,and 15322 differentially expressed genes(DEGs)were screened.To identify the differentially expressed genes that promote flowering of mango fruit in response to SPD treatment,1249 DEGs were obtained by analyzing the common DEGs among TA vs TC,TA vs TD,C vs TC and D vs TD by Wayne diagram.These DEGs are significantly enriched in starch and sucrose metabolism,plant hormone signal transduction,photosynthesis phenylpropanoid biosynthesis and circadian rhythm pathway.(3)Plant hormone signal transduction pathway,starch and sucrose metabolism,flowering regulation pathway and related genes in response to SPD regulation of mango flowering were identified.For plant hormone signal transduction pathway,Auxin signal-related genes(AUX1,AUX/IAA,SAUR),cytokinin signal-related genes(CRE1,AHP,B-ARR),gibberellin signal-related genes(DELLA,PIF3),abscisic acid signal-related genes(PP2C,ABF),ethylene signal-related genes(ETR,SIMKK,EIN3,ERF).CYCD3),jasmonic acid signal-related genes(JAR1,JAZ,MYC2)and salicylic acid signal-related genes(TGA)were differentially expressed in TA vs TC,TA vs TD,C vs TC and D vs TD.And starch sucrose metabolism,PYG,HK,ots B,endoglucanase,beta-glucosidase,INV,bgl X,bgl B,GN1＿2＿3 were differentially expressed in TA vs TC,TA vs TD,C vs TC and D vs TD.At the same time,it was found that the expression of transcription factors that positively regulate flowering,such as CO,SOC1,FT and AP1,SPL and AGL,was higher than that of the control at 80 and/or 100 days after SPD treatment.The expression of transcription factors negatively regulating flowering,such as AP2,was lower than that of the control at 80 and/or 100 days after SPD treatment.(4)The metabolomic maps of terminal buds in different development stages after SPD treatment and control treatment were constructed.A total of 582 metabolites were detected in the metabolic group,including 129 lipids,63 organic acids,49 nucleotides and their derivatives,187 phenolic acids,72 amino acids and their derivatives and 82 others.Metabolites with VIP≥1 calculated based on OPLS-DA model and difference multiple Fold Change ≥ 2(up-regulation)/Fold Change ≤ 0.5(down-regulation)were selected as screening criteria.A total of 398 different metabolites were screened from16 pairwise comparisons.(5)The key metabolites responding to SPD regulation of mango flowering were identified.After 80 ～ 100 days of SPD treatment,with the dormancy of terminal buds released,metabolites such as lipids,phenolic acids,amino acids,carbohydrates and vitamins in terminal buds changed significantly with time.Lysophosphatidylcholine(LPC)was significantly up-regulated from 80 to 100 days,and proline,ascorbic acid,carbohydrate and tannin increased continuously.But there was no significant change in the control.(6)Based on the WGCNA analysis of transcriptome and key metabolites,the key modules and genes that promote mango flowering in response to SPD were identified.Taking L-proline,L-glutamic acid,1-aminocyclopropane-1-carboxylic acid,γ-aminobutyric acid and lysophosphatidylcholine 16:2 as phenotypic data,and combining with differentially expressed genes,12 coexpression modules were constructed,among which the gene of turquoise module was related to L-proline,Lglutamic acid,1-aminocyclopropane-1-carboxylic acid and γ-aminobutyric acid.There are 4 proline proteins and 1 proline receptor highly related to L-proline.Furthermore,the coexpression network of the core genes of turquoise module was constructed.Generally speaking,from the perspective of transcription regulation,SPD can promote mango blossom by regulating plant hormone signal transduction,starch and sucrose metabolism,flowering regulation pathway and related gene expression.From the metabolic point of view,SPD can promote mango blossom by regulating the metabolic changes of lipids,phenolic acids,amino acids,carbohydrates and vitamins.At the same time,based on WGCNA analysis,the core genes related to amino acids are also discovered.