Observation Of Flower Bud Differentiation And Transcriptome Analysis Of Pistil Abortion In 'Li Guang Xing'

Gansu is one of the original centers of apricot.‘Li guang xing'(Prunus armeniaca L.var.glabra sun S.X.)is one of the three famous apricots in Gansu Province.It has a long flowering period and a large amount of flowers.However,serious pistil abortion has become one of the key factors affecting fruit bearing,yield and quality.In this experiment,the 8-year-old Li guang xing was used as the experimental material.The physiological differentiation,morphological differentiation and flower bud morphogenesis of ‘Li guang xing' were studied by paraffin section system,and the changes of endogenous hormone content,mineral elements and other physiological indexes in bud during flower bud differentiation were measured.At the same time,the abortive flowers and normal flowers were used as test materials.Based on the observation of their internal morphology,the mechanism of abortion was analyzed by transcriptome.The main results are as follows:1.There were significant differences in the percentage of abortive flowers among different trees,among which 91.26% were weak trees,87.51% were strong trees and 71.08% were middle trees.Among the fruiting branches of different types in the same tree potential,the abortion rate of flower cluster fruit branches was the lowest,which were strong trees(83.41%),middle trees(55.79%)and weak trees(93.85%).By measuring the pollen viability and germination rate of different fruiting branches,we can see that the pollen viability was: bouquet fruit branch > short fruit branch > middle fruit branch > long fruit branch,and the germination rate was: short fruit branch > bouquet fruit branch > middle fruit branch > long fruit branch.2.The differentiation of Li guang xing was completed from June 20 to early October.The differentiation process was divided into seven stages: undifferentiated stage,early differentiation stage,sepal differentiation stage,petal differentiation stage,stamen differentiation stage,pistil differentiation stage and pollen cell stage.The peak period of differentiation was concentrated from August to September,and there were overlapping phenomena in all stages.3.In late June,with the beginning of morphological differentiation,the contents of ABA and CTK decreased and maintained a low level;IAA content increased and peaked in September;the contents of ZR and GA increased first and then decreased,and peaked in September.The ratios of ABA/IAA,ABA/GA and ZR/IAA in June(undifferentiated stage)were significantly higher than those in other periods.The change of ZR/GA showed a trend of first rising and then declining,with the highest value in July and the smallest value in September(pistil differentiation stage).GA/IAA was the highest in June,and decreased gradually after entering the stage of morphological differentiation.The change of ZR/ABA showed a trend of first rising and then declining,with the highest in September.4.The content of total nitrogen and total carbon decreased until the early October differentiation,and C/N ratio increased first and then decreased.There were significant differences in starch content in leaves,branches and flower buds at different differentiation stages.In September,starch content in flower buds was the highest,and most of them were in pistil differentiation stage.The soluble sugar content of flower bud decreased significantly after the completion of flower bud differentiation,reached the highest value in September(pistil differentiation period),and the soluble sugar content of flower bud showed a trend of first decreasing and then descending,and the lowest value appeared in July.During the flower bud morphological differentiation period,more mineral elements are needed to participate in the process.The content of P and Mg first decreased and then increased,and the lowest value appeared in August,but the content of Ca,Cu,Fe,K first increased and then decreased.5.There are many types of pistil abortion.As compared with normal flowers,the pistil appearance of abortive flower is normal,but the ovary development is abnormal.Most of ovaries were characterized by uneven growth points and thin ovaries.The pistil style was lower than filament.Microstructure showed that the pollen grains of abortive flowers were decreased sharply,the ovaries shrunk and the ovule primordia developed stagnately.The hormone levels of ZR,IAA and CTK in abortive flowers decreased significantly.But the content of ABA and GA was significantly higher than that of normal flowers.6.Through RNA-Seq,6647 differentially expressed genes,including 2543up-regulated and 4104 down-regulated genes,were identified.According to the KEGG Pathway,the pyruvate metabolism,plant hormone signal transduction,spliceosome,RNA transport,protein processing in endoplasmic reticulum and other metabolic pathways were significantly enriched.It revealed that AUX1,AUX/IAA,TIR1,ARF,GH3 and SAUR,vital genes displayed identical differential expressionprofiles to auxin transduction pathway,and ABF,SnRK2,PP2 C to abscisic acid,JAZ,MYC2 to jasmonic acid.At the same time,the expression of ERF1/2(DN70415)was up-regulated in normal flowers,and ethylene may be the key regulator of the abortion of ‘Li guang xing'.