Screening And Studing Of Gibberellin-regulated F-box Genes In Arabidopsis

Gibberellins(GAs) act as one plant hormone, which play an important role in the regulation of plant growth and development, but the molecular mechanism for GA-mediated plant growth regulation remain to perfect further. F-box proteins are the subunits of SCF complex and also work as determinant the ubiquitination degration of target protein via the specific recognition of substrates, playing an important role in plant hormone signal transduction. The purpose of the study is to find out the F-box genes controlled by GA, and the results as following:(1) 38 candidate F-box genes regulated by GA were selected through the analysis of gene microarray data in Arabidopsis using bioinformatics methods, and six of which were verified by real-time PCR. Furthermore, we also found that there are thirty F-box genes have GA response elements and other elements involved in IAA, ABA, light, temperature and drought stresses or circadian clock in the promoter sequence.(2) Besides, the analysis of interactions of proteins provided by Bio Grid databases show that eighteen candidate F-box proteins have direct or indirect correlation with GA2ox1, GA3ox1 and GA3ox3. T he gene expression profiles tell us that the candidate F-box genes express at all tissues and organs in Arabidopsis, and have responses to IAA, ABA, light, temperature and drought stresses, or photoperiod.(3) To confirm the above results, one of the candidate F-box genes, FKF1 was chosen for subsequent experimental analysis. Here we found that the expression of FKF1 is down-regulated in WT Arabidopsis treated by exogenous GA3. The fkf1 mutants have short hypocotyl phenotype in blue light, which displayed increased hypocotyl growth in the presence of GA3, but the hypocotyls of fkf1 cannot completely reached to the length of WT plants. And the hypocotyl elongation of fkf1 seedlings were more sensitive to GA synthesis inhibitor, paclobutrizol(PAC) or ancymidol, when GA biosynthesis was blocked by PAC or ancymidol, the fkf1 exhibited weak hypocotyl elongation than the WT seedlings in response to GA3, but not in the dark, suggesting that the deletion of FKF1 results in reduced GA response during seedling growth in light.(4) Under the blue light and circadian rhythm influence, the expression of GA biosynthetic and catabolic genes were decreased in fkf1 mutants, and so did DELLA genes. T hese tell me that FKF1 control both downstream GA response and upstream GA biosynthesis in a light-dependent manner during seedling growth. In GA receptor mutant gid1a/b/c, the FKF1 showed weaker responsed to GA than that of wild type, indicating that it is involved in GA reponse. Moreover, the transcription levels of FKF1 were increased in the rga and gai mutants, suggesting that FKF1 and DELLA demonstrate antagonistic effect in GA signal pathway.(5) A preliminary report was confirmed that DELLA protein RGL1 has interaction with FKF1 based on yeast two-hybrid. By the technology of yeast one-hybrid, we fonud that FKF1 promoter may interact with transcription factors, including IAA5, ARF20,E2 FC,WER, SPL1, SPL15,BZIP61 and BHLH094.In conclusion, the present results preliminary suggested that FKF1 regulate the hypocotyl elongation by modulating GA biosynthesis and signal transduction in Arabidopsis.