Study On Transcript Responses Of Exogenous Plant Growth Regulators Treatment And Analysis Of The BHLH Gene Family In Cenchrus Purpureus Schumach Cv.Purple

Cenchrus purpureus Schumach cv.Purple is a perennial larger C4 herb of Tribulus genus of Gramineae,which has been widely cultivated in Southern part of China.It has been known as a world-recognized high-yield and quality gramineous forage because of its high hay yield,good palatability and high nutritional value.In addition,due to its quick regeneration,high photosynthetic efficiency,and high combustion calorific value,it can also be used as an energy grass.Elephant grass grows fast,it can grow to 150 cm in more than 20 days.However,the mechanism of C.purpurea response to plant growth regulator has not been thoroughly studied and discussed.In this study we analyzed the effects of exogenous gibberellin（GA₃）and paclobutrazol（PAC）treatment on the content of endogenous gibberellin GA₁ and GA₄ in Cenchrus purpureus Schumach cv.Purple,and on transcript responses in GA biosynthesis and signal transduction.Then,the gene family of bHLH transcription factors was analyzed,which plays an important role in regulating the growth and development of the elephant grass,and the response mechanism of Cenchrus purpureus Schumach cv.Purple to plant growth regulators was preliminarily clarified.The results are as follows:1.After treatment with exogenous GA₃,the contents of endogenous GA₁ and GA₄in C.purpurea increased significantly（P<0.05）,and the contents showed an upward trend with the increase of treatment time,which indicated that exogenous GA₃treatment may promote the accumulation of endogenous gibberellin.After treatment with exogenous PAC,the contents of GA₁ and GA₄were significantly reduced（P<0.05）,which indicated that exogenous PAC treatment could inhibit the accumulation of endogenous gibberellin.2.A total of 16,393 differentially expressed genes（DEGs）were identified by transcriptome sequencing of shoot tips treated with exogenous GA₃ and PAC（0h,1h,48h）,and about 126.53 Gb of effective sequences were obtained.Enrichment analysis of metabolic pathways showed that these DEGs were mainly enriched in biological metabolic pathways such as carbon metabolism,translation,amino acid metabolism and plant hormone signal transduction.WGCNA analysis identified 10 gene co-expression modules.The GO and KEGG enrichment and expression analysis of the module genes preliminarily confirmed that GA20ox and GID1 genes play an important role in the GA signal transduction pathway in C.purpurea.A total of 30 types of transcription factors have been identified,such as bHLH,MYB,C3H,etc.Among them,bHLH transcription factor plays an important role in the response to plant hormone signal transduction pathway of elephant grass.3.A total of 229 bHLH transcription factor members were identified at genome-wide level,which were not evenly distributed on 14 chromosomes.The results of phylogenetic analysis revealed that 229 CpbHLHs could be classified into 18 subgroups.The results of gene structure analysis showed that the bHLH transcription factors in elephant grass were similar to those in other plants,which the members of each subfamily have similar gene structures and conserved motifs.Therefore,it was speculated that the bHLH transcription factors in the same group might have similar functions.The transcriptional expression profile showed that there were 55,65 and 51,56 CpbHLH genes differentially expressed after GA₃ and PAC treatment for 1 h and 48h,respectively.qRT-PCR results showed that 9 genes were differentially expressed after exogenous GA₃ and PAC treatment,suggesting that these 9 genes may be related to GA₃ and PAC mediated signaling pathways.