Functional Study On The Regulation Of Flowering Time And Plant Height By GmGAMYB Gene In Soybean

China has a vast territory across latitudes from north to south,soybean varieties growing in the south will blossom late or even not blossom when transplanted to the north,while the northern varieties will enter the mature stage too early and lead to extremely low grain yield in the south.Therefore,flowering time is a key agronomic character that directly affects whether soybean can successfully adapt to different latitudes and farming systems.Soybean（Glycine max）is a photoperiod sensitive short-day plant.The cultivation of new soybean varieties with reduced photoperiod sensitivity and wide adaptability and early maturity is of great significance to the promotion of soybean to higher latitudes in Heilongjiang Province.Gibberellin plays a physiological role in regulating plant growth and development.GAMYB gene is the first positive regulator identified in gibberellin signal transduction pathway,which can affect the flowering time and anther number of soybean,thus controlling the growth and development process and yield traits of soybean.So far,many studies have been carried out on GmGAMYB in soybeans.However,there are relatively few studies on photoperiod sensitivity of soybean GmGAMYB gene.The study of GmGAMYB gene in gibberellin transduction pathway has important agricultural application value for the improvement of soybean growth period traits and the exploration of soybean gibberellin signal transduction pathway.The T₁ generation of transgenic GmGAMYB soybean was obtained in our laboratory.This study will further analyze the role of GmGAMYB-ox gene in soybean.Transgenic soybeans were treated with LDs and SDs,and the phenotypic characters of overexpressed soybeans were analyzed by observing flowering and agronomic traits.The promoter sequence of GmGAMYB gene was analyzed by Plant CARE and PLACE online prediction tools.The transcriptome sequence of GmGAMYB gene was sequenced by RNA-seq technique.The internode cell morphology of GmGAMYB-ox and WT soybean was observed by scanning electron microscope.The sensitivity of GmGAMYB-mediated GAs hypocotyl elongation was determined by gibberellin administration.The main experimental results are as follows:（1）Under long-day and short-day conditions,the phenotypes of two T₃ generation GmGAMYB-ox soybean lines were tall and early flowering.（2）The cis-acting elements prediction of the promoter sequence of GmGAMYB gene were carried out by using Plant CARE and PLACE websites,and it was found that it was rich in a large number of light-response elements（3-AF1 binding site,AE-box,AT1-motif,Box 4,G-Box,TCT-motif）and a gibberellin response element（GARE-motif）.It is speculated that the promotion of early flowering by GmGAMYB gene may be caused by a large number of light response elements,and the phenotype of higher plant height of GmGAMYB-ox may also be regulated by gibberellin.（3）The transgenic GmGAMYB soybean was sequenced by RNA-seq.The results showed that the expression of three members of soybean FUL gene family was significantly up-regulated,so it is speculated that GmGAMYB gene may promote early flowering of soybean by positively regulating the expression of Gm FULc,Gm FUL1a and Gm FUL2b genes.GmGAMYB is regulating three genes related to plant height regulation:gibberellin 20-oxidase（GmGA20ox,Glyma.09G149200）,Gm TCP8（Glyma.05G027400）and Gm TCP12（Glyma.06G193000）.It is speculated that the plant height of GmGAMYB-ox is significantly higher than that of WT,which may be the result of GmGAMYB up-regulation of GmGA20ox expression.RNA-seq sequencing was performed on T₂generation transgenic soybean GmGAMYB.The results showed that the expressions of three members of the FUL gene family（Gm FULc,Gm FUL1a and Gm FUL2b）were significantly up-regulated,which suggested that GmGAMYB might promote the early flowering of soybean by positively regulating the expressions of Gm FULc,Gm FUL1a and Gm FUL2b.GmGAMYB positively regulates three genes related to plant height regulation:gibberellin 20-oxidase（GmGA20ox,Glyma.09G149200）,Gm TCP8（Glyma.05G027400）and Gm TCP12（Glyma.06G193000）.The significantly higher plant height of GmGAMYB-ox than WT might be the result of GmGAMYB upregulating the expression of GmGA20ox to increase plant height.（4）The hypocotyl of GmGAMYB-ox transgenic soybean seedlings induced by exogenous GAs was significantly longer than that of WT seedlings.The results showed that the sensitivity of transgenic soybean with GmGAMYB-ox gene to gibberellin was higher than that of WT,GmGAMYB as a positive response factor of GAs pathway.In addition,the stem epidermal cells of transgenic soybean GmGAMYB-ox and WT were observed by scanning microscope,and it was found that the height of GmGAMYB-ox soybean was caused by the increase of internode cells in the stem.