| Taking the dwarf mutant abs1-1D as its subject, aimed at analysising the relationshipbetween abs1-1D and BR, the study investigated the function and expression pattern of ABS1.At the same time, I did some research about ABS1homologous gene At5g47980. The mainresults are as follows:(1) A dwarf mutant, abs1-1D, significantly different from wild type during plant growthand development was obtained from Arabidopsis mutant library established by activationtagging. Compared with wild type, abs1-1D present seriously dwarf phenotype. The leaves ofabs1-1D were abnormal curvature and could not be fully expanded. Plants of abs1-1Ddeveloped fewer leaves, deeper leaf color and shorter petioles compared with that of wild type.And abs1-1D is a semi-dominant dwarf mutant.(2) After the Southern hybridization, I found the activation tagging T-DNA was linkedwith abs1-1D dwarf phenotype. With the help of plasmid rescue technique, I found theT-DNA was inserted in chromosome IV between At4g15400and At4g15410. The right borderof T-DNA was adjacent toward to At4g15400. The result of Northern hybridization helps usto know that the expression level of At4g15400was significantly increased in abs1-1D.(3) A binary vector which consists of At4g15400full-length cDNA controlled byconstitutive CaMV35S promoter was constructed to transform into wild-type Arabidopsis.The phenotype of transgenic lines was similar to abs1-1D. Expression profiles revealed bysemi-quantitative RT-PCR showed that，the expression level of ABS1was significantly highin these transgenic dwarf plants. All these results suggest that, overexpression of At4g15400is the cause of dwarf phenotype of abs1-1D. That is to say, At4g15400is ABS1.(4) The insertion site of abs1-1T-DNA mutant (WiscDsLox474E11) is in the ABS1coding region,49base pairs apart from the stop codon. Expression profiles revealed bysemi-quantitative RT-PCR showed that, full-length ABS1transcripts were not detectable inabs1-1plants. There were no obviously phenotypic differences between abs1-1and wild typeunder light condition. Seven days old abs1-1seedlings showed significantly enhancedelongation of hypocotyl compared with that of wild type under dark condition.(5) Though the result of sequence alignment, I found that ABS1is a member of BAHDacyltransferases, there are two conserved motifs (HXXXD and DFGSG) of in ABS1amino acid sequence. The two closest homologues of ABS1are At5g47980and At5g23970, whichshare51.7%and42.1%amino acid identity with ABS1, respectively.(6) Expression profiles revealed by semi-quantitative RT-PCR showed that, ABS1ishighly expressed in root tissue. Low expression detected in seedlings, rosette leaves, siliqueand flower. For At5g47980, we detected the expression of it in the root tissue only. At5g23970is mainly expressed in flowers. A binary vector consisting of a GUS fusion controlled byABS1promoter was transformed into wild-type plants. The result of GUS staining fortransgenic plants shows that, ABS1mainly expressed in root, hydathodes and silique. Thesub-cellular localization results showed that, ABS1was localized in cytoplasm.(7) The dwarf phenotype of abs1-1D is similar with that of mutants which are short ofBR or in which the BR signal transduction is blocked. The chlorophyll content was not onlyhigher in abs1-1D than that of wild-type plants. Chlorophyll content in ABS1overexpressingplants was also higher than that of wild-type plants. The hypocotyl length of abs1-1D wassignificantly shorter compared with that of wild type grown in the dark for7days. The resultof longitudinal sections of leaf petioles shows that, cell length of abs1-1D and det2-1,which isshort of BR, significantly reduced when compared with those of wild-type plants.(8) We found that phenotypes of abs1-1D and det2-1were rescued by being growndirectly or transplantation into MS medium containing epi-BL. The elongation of leafpetioles，the expansion of leaves and the elongation of hypocotyls were discovered inabs1-1D and det2-1in MS medium containing epi-BL. Expression profiles revealed bysemi-quantitative RT-PCR showed that, classic BR biosynthesis genes were highly expressedin abs1-1D, OE-1, OE-3, and det2-1plants when compared with those expressed in wild type.The expression of ABS1and At5g47980were increased in wild-type plants under thetreatment of epi-BL, against this, the expression of CPD and DWF4were decreased. Thetranscription level of ABS1was induced and that of CPD was reduced in bes1-D.(9) The results of genetic analyses show that, there are synergistic interactions betweenthe function of ABS1and DET2, bes1-D, which is a BR constitutive signal transductionmutant, is a genetic suppressor of abs1-1D, overexpression of ABS1can inhibit thephytochrome gene PHYTOCHROME B mutant phyB-1mutate phenotype.(10) According to the results of gene chip, there were383genes up regulated in abs1-1Dfor two times or more,238genes down regulated for two times or more. Many genes involvedin BR biosynthesis pathway were up regulated in abs1-1D. Other genes related to flavonoidbiosynthesis pathway were down regulated, such as some TT family members.(11) We found that dwarf is also a phenotype of At5g47980overexpressing lines.However, the dwarf tendency of At5g47980overexpressing lines is not obviously as abs1-1D plants. From the phyllotaxis arrangement of At5g47980overexpressing lines, the leaf numberof them was less than that of wild-type plants, and the leaves were more round. At5g47980overexpressing lines became de-etiolated under dark condition. Poor fertility can be found inAt5g47980overexpressing lines. The result of GUS staining for transgenic plants, into whichwas transformed a binary vector consisting of GUS fusion controlled by At5g47980promoter,combined with the expression profiles revealed by semi-quantitative RT-PCR, show that,At5g47980only expressed in root. |
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