Regulation Of DgD14 And DgD27 Gene In Shoot Branching Of Dendranthema Grandiflorum ’jinba’

Shoot branching plays an important role in determining plant architecture, and has a highly plastic response to environmental stresses. Auxin and Strigolactones (SLs) negatively regulate shoot branching through interaction with auxins, while cytokinins provide a balance to regulate shoot branching. SLs can also respond to conditions of low or absent phosphate or nitrogen to play important roles in the regulation of plant architecture. Recently, the reasech of SLs pathway in regulating shoot branching in chrysanthemum were preliminary, the molecular nature of their function in respond to conditions of low or absent phosphate or nitrogen is as yet uncharacterized. Here, we further analyzed roles of DgD14 and DgD27 in regulation of shoot branching in chrysanthemum(Dendranthema grandiflorum ’Jinba’).The results are shown as belows.1) The D14 gene encodes a protein of the α/β-fold hydrolase superfamily, which is a probable candidate as an SL receptor in rice, petunia, and Arabidopsis. To investigate the roles of D14 in shoot branching of chrysanthemum, we isolated the D14 homolog DgD14. Functional analysis showed that DgD14 is a nuclear-localized protein. Gene expression analysis revealed that DgD14 was expressed at the highest levels in stem, was weakly expressed in root, and was up-regulated by exogenous auxin. We obtained 1588 bp promoter sequence, which has ABA and GA response element. DgD14 could complementated of Arabidopsis d14-1. Decapitation could down-regulate DgD14 expression, but this effect could be restored by exogenous auxin. In addition, DgD14 transcripts produced rapid responses in shoot and root under conditions of phosphate absence, but only mild variation in bud and stem with low nitrogen treatment. Indistinct reductions of P levels in shoot were observed in plants grown under low nitrogen conditions. The absence of phosphate and low levels of nitrogen negatively affected plant growth; this resulted in a decrease in FW (fresh weight) and the number of shoot branches, and also promoted PR (primary root) elongation. These results demonstrated that P levels in shoots had a close relationship with the fact that N did not directly regulate DgD14 expression in shoots. Taken together, these results demonstrated that DgD14 played an important role in shoot branching of chrysanthemum.2) The D27 gene encodes an iron-containing protein, which acts upstream of CCD7 and CCD8 in the SLs biosynthesis pathway in rice and Arabidopsis. To investigate the roles of D27 in shoot branching of chrysanthemum, we isolated the D27 homolog DgD27, and obtained 1588 bp promoter sequence. Functional analysis showed that DgD27 is a plastid-localized protein. Gene expression analysis revealed that DgD27 was expressed at the highest levels in stem, was weakly expressed in leaf and petiole, and was up-regulated by exogenous auxin. DgD27 could complementated of Arabidopsis d.27-1. DgD27 responded to CKs and GA both in buds and stems might play different roles in response to hormone treatments in the regulation of shoot branching. The dark treatment negatively affected plant growth and could down-regulate DgD27 expression in bud. Decapitation could down-regulate DgD27 expression, but this effect could be restored by exogenous auxin. In addition, DgD27 transcripts produced rapid responses in shoot and root under conditions of phosphate absence, but only mild variation in bud, stem, and root with low nitrogen treatment. DgBRCl transcripts produced mild variation in bud with low nitrogen treatment, which demonstrate that nitrogen regulates shoot branching not via SLs pathway. Different hormone types respond to conditions of phosphate absence and low nitrogen treatment in chrysanthemum. The levels of IAA, ZR, and ABA aused by P deficiency in bud, while the levels of IAA and ABA aused by low N treatment in bud, and there was no difference in he level of GA under P deficiency or low N treatment. The over expression of DgD27 transgene into chrysanthemum, we get the transgenic plants. These results demonstrated that DgD27 played an important role in shoot branching of chrysanthemum.In summary, we suggest that DgD14 and DgD27 play an important role in shoot branching of chrysanthemum, and can respond to conditions of light, low or absent phosphate or nitrogen in regulating shoot branching in chrysanthemum.