The Research On Molecular Mechanism Of Tillering Development And Identification Of PvMAX2 And TCP Transcription Gene Family In Switchgrass

Switchgrass?Panicum virgatum L.?is a perennial C₄ plant that is widely used as a source of biofuel and for soil and water conservation.Under extreme conditions,switchgrass can produce a large number of tillers,which is one of the most significant factors contributing to the formation of biological yield.Therefore,research on the molecular mechanisms underlying tiller formation has important implication with respect to the genetic improvement of switchgrass.Furthermore,the insight gained from research on this crop will provide a valuable reference for studies on other crops.In this study,two relative EMS mutagenic mutants?multi-tiller and small-tiller mutants abbreviated ht and lt?were used for physiological,biochemical,and cytological analyses to examine the mechanisms underlying tiller formation in switchgrass.We also performed a comparative analysis of the genetic transcription differences between the two mutants?Ht and It?.The key gene PvMAX2 in the strigolactone pathway of switchgrass,was cloned and its biological function was verified.In addition,downstream regulatory genes in the monocaprolactone pathway of the TCP family of transcription factor genes were identified and analyzed.The results of these analyses will provide a basis for studying the mechanism of tillering regulation in switchgrass.The following are the main results of this study.?1?Analyses of paraffin sections of the stem base of the Ht mutant and mutant phenotype showed that differences in tiller number can be attributed to differences in tiller bud elongation rate.After topping,the elongation rate of the tiller bud in lt was significantly slower than that of the ht mutant,which indicated that the elongation rate of tiller bud and the stem base of tiller bud have similar regulatory mechanisms.The content of stolonolactone and abscisic acid in the mutants lt showed that the synthesis and signal of the mutant were stronger than those of the ht mutant,which indicated that the aboveground parts of the mutant show less response to gravity than those of the Ht mutant.These differences can probably be ascribed to the different effects of strigolactone content in the transport of auxin.?2?There were 5410 genes with more than twofold differences between the transcription of ht and lt mutants.Among these genes,2065 were up-regulated and 3345were down-regulated.These genes are involved in several biological processes,particularly those related to responses to environmental stimuli and plant hormone signal transduction pathways.?3?With reference to the published sequences of the genomes of switchgrass and other species,we designed primers and cloned the key gene PvMAX2.The expression pattern of PvMAX2 was analyzed and found to be present in all tissues.The results showed that expression levels were higher in roots and stems than in other tissues.In addition,over-expression of PvMAX2 in the Arabidopsis thaliana MAX2 mutant was found to effectively increase the number of tillers,thereby indicating the conserved function of the PvMAX2 and A.thaliana MAX2 proteins.?4?The TB1/FC1 gene is an important downstream response gene in the strigolactone pathway.TB1 is a member of the TCP transcription gene family.A total of 41 TCP transcription factors were identified in the entire switchgrass genome,which were evenly distributed on the switchgrass chromosomes.These genes can be divided into two subfamilies,namely TCP-P and TCP-C.Analysis of conserved structure and gene structure on this family of genes in A.thaliana,rice,and switchgrass revealed that family members in rice and switchgrass showed the closest relationships.The results of tissue expression analysis revealed that different TCP members have different expression patterns in different tissues,which indicates that these TCP members may have different effects on developmental processes in switchgrass.