| Gibberellin and its inhibitor uniconazole,a kind of high efficient plant growth regulator.are comprehensively used in crops,fruit trees and ornamental plants to strongthen seedlings,control plant height,increase yield.Regulatory mechanism of these plant growth regulators become a research hotspot.The root system is an essential organ of-soybean,which anchors the plant in its substrate,mines water and mineral,plays a role in biological fixation of nitrogen.So,study of the regulatory mechanism of regulators on soybean root system contributes to explain the regulation function of gibberellin and uniconazole.In this study,soybean seed were treated with GA3 and uniconazole solution by seed soaking,and the root morphology,anatomical structure of root,physiological activity and transcriptomics were studied to explore the regulation effect of GA3 and uniconazole on soybean root.Moreover,the the effect of GA3 and uniconazole on soybean agronomic traits were also investigated.The detailed results are as follows:This study showed that GA3 and uniconazole have opposite effects on root morphology.GA3 treatment by seed soaking resulted in thinner root diameter,shorter root,reduced root surface area and root volume,little apical number at 4 days,and the difference became larger with the increasing of concentrations of GA3.In addition,GA3 treatment also promoted the formation of lateral root primordiums in early phage,and the number of lateral root primordiums in the treatment group was significantly higher than that of the control group at 72 h,but the number of lateral root in the treatment group was significantly decreased at 96 h,which indicated GA3 treatment was not beneficial to the development of lateral root primordiums to lateral roots.Uniconazole treatment resulted in thicker of roots diameter,longer root,more root tips,and increased root surface and root volume.The gradient effect is observed.Root microstructure results showed that 30,60 mg·L-1 exogenous GA3 treatments resulted in a significant decrease of the thickness of the cortex,a smaller diameter of the central sheath and a smaller cell size,and the blurry boundaries of the primary and the secondary layers of the cell wall,and the root development is inhibited.Uniconazole treatment increased the thickness of the main cortex and the size of the cortical parenchyma cells at 60 h and 72 h.Physiological study showed that GA3 treatment kept the content of GA3 in a high level all the time.Uniconazole treatment significantly decreased the content of GA in root(1d and 3 d),and the effect disappeared on the 5th day,and the content of GA bounced on the 10th day,which may be caused by the feedback regulation.On the first day after treatment,the high concentration of uniconazole decreased the content of IAA,and the content of IAA bounced on the 5th day.Uniconazole treatment also has a certain effect on oxidase of reactive oxygen scavenging.and 1mg L-1 uniconazole treatment increased the activity of SOD and CAT enzyme at 12 h.Transcriptome sequencing results showed that in transcriptome profile of root after GA3 treatment,a total of 1317 different expression gene(DEGs)were identified,and 377 DEGs were up-regulated,while 943 DEGs were down-regulated.KEGG enrichment analysis showed that those DEGs distributed in 76 metabolism pathways,and plant-pathogen interaction(PATH:ko04626)and plant hormone signal transduction(PATH:ko04075)were dominant pathways.In order to adapt to the high concentration of GA,3 GA20ox in gibberellin biosynthesis pathway was down-regulated.Except for the GA biosynthsis patheway,the GA signal pathway was also significantly affected.GA receptor F-box protein GID2,acyl-activating enzyme 12,FMO GS-OX5 etc and transcript factors bHLH130,MYB39,RAX2,PWRKY53 were down-regulated,while acyl-activating enzyme 5 and transcript factors Myb15,LEP,RAX3,Snakin-2 were up-regulated.There were 58 DEGs related to cell wall biogenesis and degradation,including the downregulation of cell wall loosing related DEGs,such as 1 expansin and 10 glucosidase.The downregulation of these genes may contribute to the smaller cortical cells.The downregulation of glucosidase is identical to the activity decrease of glucosidase.GA3 treatment also affects the pathway of phenylethane and its branch pathway flavonoid pathway which participate in the synthesis of lignin,and the differential expression of these genes should be related to cell wall changes.Reinforcement of cell walls by the deposition of extensin may be a general requirement for penetration of the root cortex by a newly formed meristem,and there are 8 extensin proteins down-regulated among DEGs in root.qRT-PCR of 3 EXTs genes showed that those genes were all down-regulated at the different timepoints.The different expression of extensin genes was one of reasons of the morphology changes of soybean cell and make the lateral root primordium difficult to breakthrough the root cortex.Transcriptome of root after uniconazole treatment showed there were 1269 DEGs detected 5 and 592 DEGs were activated,while 677 DEGs were down-regulated.These DEGs belonged to 67 KEGG pathways,and plant-pathogen interaction(PATH:ko04626)and plant hormone signal transduction(PATH:ko04075)were also dominant pathways.Transcriptome of root showed that the important oxidases in GA synthesis pathway were up-regulated,which reflects a feedback regulation of plant to the low concentration of GA.Meanwhile,uniconazole treatment also affect regulation genes of GA biosynthesis pathway.Analyses of phytohormone-associated genes for endogenous hormones changes showed the strong upregulation of ethylene biosynthesis key enzyme ACS gene(log2FC 7.56):and ethylene response factor ERF1 and ERF 109(log2FC>5),and the expression of ERF109 were all up-regulated at the different timepoints.ERF1 and ERF109 in ethylene signal pathway interact with PXY signal pathway to maintain cell division of vascular bundle.So,this pathway is proposed as one of the main pathways that uniconazole affects root growth,the results indicated that plant hormone signal transduction and interaction play a important role in the uniconazole regulation of root development.Besides,some DEGs were related to cell division and cell wall modification.Therefore,the transcriptome of the soybean root indicated that the changes in the morphology of soybean roots induced by uniconazole treatment may be related to the several molecular networks,including plant hormones signaling pathway,crosstalk of hormones,the regulation network of various transcription factors,genes related to cell division and cell wall modification.The study of effect of plant growth regulator on agronomic traits by soaking seed showed that GA3 treatment by seed soaking increased the plant height of soybean seedling,and uniconazole treatment by seed soaking inhibited the plant height of soybean seedling.In the harvest period,the plant height of the high concentration of 60 mg·L-1 GA3 treatment was lower than that of control,and the length of 3th and 12th-14th knots were significantly lower than those in the control group which lead to the significantly decrease of plant height.GA3 and uniconazole treatment both increase the width of internodes,and 30 mg·L-1 GA3 treatment and 0.25 mg·L-1 uniconazole treatment showed the maximal increase slope.GA3 treatment decreased the petiole length on the bottom and increased the petiole length on the top,and uniconazole treatment increased the petiole length on the bottom.Both regulators changed the canopy structure.In the seedling period,0.25 mg·L-1,1 mg·L-1 uniconazole treatment signiificantly increased the content of chlorophyll,and 60 mg·L-1 GA3 treatment significantly reduced the chlorophyll content.In the flowering period,0.25 mg·L-1 uniconazole treatment and 15 mg-L"1 GA3 treatment significantly increased transpiration rate,stomatal conductance,net photosynthetic rate.0.25 mg·L-1 uniconazole treatment significantly increased the number of grains per plant,the pods number per plant and the theoretical yield,and the mean amount of production increase were 599 kg·hm-2,by 15.14%. |
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