Analysis Of Key Genes Regulating Stamen Petaloidy In Lagerstroemia Speciosa

Lagerstroemia speciosa L.(Lythraceae),a large deciduous or semi-deciduous tree species,is plentifully applied in tropical or sub-tropical urban landscapes with numerous purple flowers blooming in summer.For the first time a double-flower variant with all stamens petaloid has been discovered among the whole genus.In this research,the morphologies and transcriptomes of single-(S)and double-flower(D)buds at three stamen developing stages have been contrasted.Measurement of gene expression can provide important clues about the molecular basis of this variation.The main results can be concluded as below:(1)All anthers in single flowers growed as usual while were totally converted into petal-like tissue in double flowers.The floral organ differentiation in L.speciosa buds is similar to regular plants as been studied.However,it takes quite little time on the differentiation of petal primordium,and probably the carpel and stamen primordia differentiate at the same time.The three organs developed rapidly once the carpel had grown up to cover the ovule.It was the key point for anther development when the diameter of bud was around 0.3 cm.In double flowers,the connection between epidermal cells of petal and petaloid stamen was reduced as they were covered by less cell wall lines.(2)The expression of most DEGs involved in plant hormone signals and transcription factors were down-regulated.DEGs involved in AUX,JA and GA signal transduction showed significant different expressions.In the regulation of transcription factors,3 MADS-box family genes Unigene0022847(AG),Unigene0026169(MADS16),Unigene0056437(AG1)were significantly differently expressed,and TF families like MYB?ERF?bHLH also had important regulation.(3)13 key genes were predicted to regulate stamen petaloidy in double flowers,and other four foral homeotic genes(MADS16,Unigene0026169;AP2,Unigene0042732;SOC1,Unigene0046314;AG,Unigene0056437)were highly involved in this variation.WGCNA was conducted and highly co-expressed genes were identified.A highly co-expressed gene network in Module brown has been constructed to have a key regulation to stamen petaloidy,in which the gene expressions were generally conserved during the three stages but significantly different in the two kinds of flowers.DEGs involved in plant hormone,TF,protein modification or degradation and biotic stress had a significant regulation to stamen petaloidy in this module.(4)Based on gene cloning,the expression vector of the key DEG Unigene0056437(AG)has been constructed and transferred into wild Arabidopsis and ag mutant to identify gene function.As a result,the robust transcriptional regulation of stamen petaloidy in double-flower L.speciosa was deduced.The comprehensive expression data in this study have been analyzed innovatively in this species up to date.It will help unravel the regulatory mechanism of several specific genes in stamen petaloidy and therefore serve as resource of double-flower molecular breeding in this species or even the whole genus.