The Changes In Morphology And Transcriptome Of Lodicules During Floret Opening And Closing In Barley

Artificial regulation of floret opening and closing is an important attempt to control anthesis,which in turn to obtain the synchronization of anthesis between parents in hybrid seed production.Lodicules are the two diminutive organs lying between the lemma and the ovary basis in the grass floret.At anthesis of cereal crops,rapid swelling and subsequent wilting of the lodicules plays a crucial role in mediating floret opening and closing.Barley is the fourth largest cereal crop in the world,but the utilization of heterosis for it has not yet been practically applied.One of the critical reasons is that most of the cultivated barley are cleistogamous and very few information on their floret opening and closing has been achieved till present.In this research,therefore,the morphological characteristics of lodicules of a non-cleistogamous barley cultivar Hu 1154 were well investigated during the process of the floret opening and closing.Furthermore,the transcriptiona]profile of lodicu]es during the process of the floret opening and closing was also scanned by RNA-Seq analysis.The following results were obtained:(1)The change in the lodicule size was synergistic with the stamen development and exsertion.During the floret opening process,the thickness of lodicules varied continuously,whereas the width of lodicules only changed when the floret was open to the maximum stage.The maximum volume of the lodicule during the opening process was approximately 1.6 times of the initial stage.(2)In lodicule,only the specific parenchyma cells surround the vascular bundle changed with the process of floret opening.Prior to floret opening,these parenchyma cells in lodicule accumulated a great amount of starch granules inside,and existed in a bent shape.During the floret opening process,their cell wall started to stretch,then the volume gradually enlarged coupled with the starch granules degrading.When the floret opening finished,the structure of these parenchyma cells gradually collapsed which finally led to their death.(3)The results of transcriptome analysis showed that a total of 10005 differential expression genes were detected in response to the process of floret opening and closing.PCA analysis indicated that six stages(prior stage S1,initial stage of opening S,median stage of opening S3,maximum stage of opening S4,median stage of closing S5 and final stage of closing S6)during the floret opening and closing could be classified into 4 groups,i.e.S1.S2,S3-S5 and S6.There were 974 genes showing the similar changing trend along with the process of floret opening and closing.(4)The morphological changing of lodicules was mainly resulted from the changes of cell wall structure and intracellular concentrations of K+ and soluble sugars.Of them,K+ was mainly transported by the channels like AKT2 and SKOR.and soluble sugars were degraded from polysaccharide or transported from vascular bundles.(5)Serine/threonine protein kinase 1,which the homologous alignment with CIPK14 in Arabidopsis thaliana,was expressed drastically in the S3 and S5 stages during the process of floret opening and closing,suggesting a possible role of it in regulating the floret opening-closing in barley.