Mining And Functional Identification Of Branching Angle Related Genes In Crape Myrtle

Plant architecture can contribute to economically valuable properties of crops and horticultural plants.Improving plant architecture is increasingly valued by plant breeders.Among ornamental plants,varied plant architectures provide natural beauty.Branching angle is a vital plant architecture characteristic that has a great contribution to the formation of plant architecture.In recent years,researches on branching angles have been increasing,mainly focusing on Gramineae,such as rice and corn.However,the regulatory mechanism of controlling the branching angle is poorly understood in woody plants.Crape myrtle,which exhibits various plant architectures,has a large number of flowers and a long flowering period.Therefore,Lagerstroemia are widely used in gardens.Lagerstroemia are rich in branching angles and suitable materials for studying the branching angle mechanism of woody plants.To investigate the branching angle mechanism,phenotypic analysis,exogenous GA₃ treat,transcriptional profiling and virus induced gene silencing in extreme branch angle progenies from a BC₁population was performed.The BC₁ population were derived from the backcross of individual with large branch angles?female?in F₁ population and L.fauriei?male?.The F₁ population was generated from L.fauriei?female?and L.indica‘Creole'?male?.The main results are as follows:?1?The 174 progenies in the BC₁ population were arranged from large to small according to the branching angle.The average branching angle of the first 10 progenies was 66.95°,which constituted an extreme pool of large branching angle and was denoted as W type.The average branching angle of the last 10 progenies was 12.51°,which constituted an extreme pool of small branching angle and was denoted as U type.Among U-type and W-type crape myrtle,plant canopy angle and plant height were significantly different.In the paraffin sections,U type exhibited obvious endodermal cells and phloem fibers,while W type did not.The axillary buds of W-type plants showed large branching angle just after germination.At six-internode stage,the bending growth of branches had been completed.Then,the branches gradually grew in the horizontal direction or in the direction of gravity,and finally drooped.While,U type grew in the direction of negative gravity throughout the growing season.After exogenous GA₃ treatment,the new branches from W type grew in a negatively geotropic manner and inhibited bending.However,the growth direction of the previous branches did not change.They indicated that the branching angle mainly determined during the early development of buds.?2?KEGG enrichment analysis indicated that starch and sucrose metabolism,circadian rhythm-plant,phenylpropanoid biosynthesis and plant hormone signal transduction pathways may be involved in the regulation of the branch angle in Lagerstroemia.Weighted gene co-expression network analysis indicated that hormone-related pathways,including diterpenoid biosynthesis,brassinosteroid biosynthesis and plant hormone signal transduction were related to the regulation of the branch angle in Lagerstroemia.In addition,starch and sucrose metabolism,flavonoid biosynthesis,phenylalanine metabolism and phenylpropanoid biosynthesis pathways were also strongly correlated with branching angle and significantly enriched.?3?A negative element of GA signaling,Lfi GRAS1,possessed higher transcription level in axillary shoots and stems of W type than it in U type.Reducing the expression of Lfi GRAS1 could decrease the branching angle and rescue or delay the bending of some new branches in W type.It indicated that Lfi GRAS1 can regulate the branching angle in Lagerstroemia.The expression level of Lfi GA2ox in W-type axillary buds,axillary shoot,and stems was significantly higher than that of U type in the same tissue.The Lfi GA2ox-silenced plants had more axillary buds.Lfi DAD2 is highly expressed in axillary buds and axillary shoots of U type.Inhibiting the expression level of Lfi DAD2 could promote the growth of axillary buds in U type.It indicated that Lfi GA2ox and Lfi DAD2 can regulate the branching number in Lagerstroemia.The study preliminary analyzed the key genes that regulate the branch angle by analyzing the key factors affecting the branch angle in Lagerstroemia.The results of this study provided candidate genes and theoretical basis for the targeted cultivation of Lagerstroemia.