Effect Of Phytohormones On Lagerstroemia Plant Height And Isolation Of Key Genes Regulating Plant Height

Plant architecture is closely connected with the yield,quality and ornamental value of crop,horticultural and ornamental plants.Plants with different growth habits that may generate economic or ornamental value are in great demand by orchards and nurseries.However,the molecular basis of the architecture of woody perennial plants is poorly understood due to the complexity of the phenotypic and regulatory relationships.Plant height is one of the most important characters of plant architecture.It is always a popular research topic.Internode cellular patterning in stems which refers to the cell number and cell size contributing to the internode length,and phytohormone regulation have become two important aspects in researching the plant height of woody plants.To elucidate the molecular mechanism of plant height and excavate the key genes modulating plant height of Lagerstroemia,the non-dwarf and dwarf progenies from the F1 population of L.fauriei(non-dwarf)and L.indica'Pocomoke'(dwarf)were used as experimental materials.The phenotype,histology and phytohormone metabolite levels were investigated,and the effects of exogenous hormones on the non-dwarf and dwarf progenies were analyzed.Transcriptional profilings of non-dwarf and dwarf crapemyrtles were performed,and potential target genes and their metabolic pathways were identified to reveal the morphophysiological changes,including changes in the phenotype,anatomy and endogenous hormone levels.The bioinformatics and gene expression analyses were used to analyze the expression rules of genes regulating the Lagerstroemia plant height.The function of key gene was confirmed through transforming Nicotiana tabacum.The main conclusions are shown as follows:1.Analyses on phenotypes related to Lagerstroemia plant height indicated that branch length was a critical determinant of Lagerstroemia plant height.The branch length of Lagerstroemia was determined by internode length instead of internode number.Therefore,internode length was used as the breakthrough point to study the plant height of crape myrtle.Anatomy analysis showed that the reduced internode length of dwarf progenies resulted from a decrease in the cell number of pith and xylem and a reduction in the elongation capability of xylem cells.Phytohormone determinant showed that auxin might play important roles in regulating cell division within SAM and cell elongation after these cells leaving the SAM to regulate the internode length.GA4 was also important phytohormone affecting the cell elongation in Lagerstroemia.2.To further explore the regulation of phytohormone on plant height,exogenous hormones were treate to the non-dwarf and dwarf progenies.The results showed that the insufficient auxin transport or abnormal signalling pathway might be principle reasons resulting in the reduced internode length of dwarf progenies.Exogenous GA4 might partly rescue the defective auxin pathway,thereby increasing the cell number within the SAM and the cell length of internode in the dwarf progenies.Additionally,the exogenous GA4 seemed to enhance the apical dominance of the dwarf progenies,which led to decreased branching number.3.Combined the results on phenotype,histology and phytohormone metabolite levels with the transcriptome analyses,the differentially expressed genes(DEGs)involved in the regulation of auxin transport and signalling pathways as well as three CYCD genes and two TCP transcription factors were finally identified.The 12 screened genes named LfiIAA26,LfiAUX22,LfiRF1,LfiARF9,LfiPIN1 LfiPINIC,LfiPIN5,LfiCYCD3;1,LfiCYCD5;1,LfiCYCD6;1,LfiTCP12 and LfiTCP14.4.To preliminarily verify the funtions of genes,LfiAUX22,LfiARFl,LfiCYCD3;1,LfiCYCD5;1,LfaCYCD6;1,LfiTCP12 and LfiTCP14 were cloned and analyzed by bioinformatics.The results showed that the protein sequences of different members belonging to the same family not only contain the conserved domain of the family,but also have their own sequence specificity.Subcellular localization results indicated that LfiAUX22,LfiARF1,LfiCYCD6;1 were located exclusively in the nucleus.LfiCYCD3;1,LfiCYCD5;1,LfiTCP12 and LfiTCP14 were mainly located in the nucleus,suggesting that they play major roles in the nucleus.5.Further gene expression analyses indicated that the LfiIAA26,LfiARF1,LflARF9,LfiPIN1,LfiPINIC,LfiPIIN5,LfiCYCD3;1,LfiCYCD5;1,LfiCYCD6;1,LfiTCP12 and LfiTCP1 were key genes involved in regulating the Lagerstroemia plant height.The expression of these genes showed significant differences in different tissues between non-dwarf and dwarf progenies.After GA4 treatment,the expression of these genes was significantly different.The expression levels of these genes all changed most significantly at 30min after GA4 treatment.6.The result of PCR confirmed the transgenic tobacco whose genome harbored LfiCYCD3;1 gene The expression of LfiCYCD3;1 was further detected by qRT-PCR in T3 plants.Phenotype determination showed that the plant height of transgenic tobacco was significantly higher than that of the control plants,and the transgenic potted tobacco was observed with curved stem.Analyses of longitudinal sections of stem segments indicated that there were no significant differences on cell length between the transgenic plants and control plants in tissue culture.While the cell number of transgenic plants was significantly increased.Results suggested that LfiCYCD3;1 was crucial gene contributing to cell division and further regulating the branch morphogenesisThese findings will provide a foundation for elucidating the molecular mechanism of plant height of woody plants and improve the efficiency of ornamental plant molecular breeding.