Regulation Of Silique Morphology By Ovate Family Protein AtOFP15 In Arabidopsis

Transcription factors are trans-acting factors that can regulate gene expression via interacting with cis-acting elements in the promoter region of their target genes.Transcription factors play important roles in regulating plant growth and development,hormone responses,secondary metabolism and stress resistance.Ovate Family Proteins(OFPs)is a plant specific family of transcription factors that regulate multiple aspects of plant growth and development.Functions of OFP transcription factors have been reported in several different plants including Arabidopsis,banana,tomato and rice.Arabidopsis thaliana OFPs(AtOFPs)family contains 19 members.Out of them,AtOFP15 has been reported to regulate silique morphology.To further characterize AtOFP15's function in regulating silique morphology,we first generated GFP-AtOFP15 fusion protein to examine its subcellular localization,and found that AtOFP15 is located in the nucleus.By using protoplast transient transfection assays,we further confirmed that AtOFP15 functions as a transcriptional repressor.To examine whether AtOFP15 functions as a passive or activate repressor,we fused the strong activator VP16 with AtOFP15,and examined AtOFP15-VP16's transcriptional activities in transient transfected protoplast.We found that AtOFP15-VP16 function as a transcription activator,indicating that AtOFP15 is a passive repressor.The blunt-end silique phenotype observed in the AtOFP15 overexpressing plants is similar to that in the erecta(er)mutants,suggesting that AtOFP15 and ER may function in the same signaling pathway to regulate plant growth and development.To examine whether that is the case,we overexpressed ER in the transgenic plants overexpressing AtOFP15,and we found the AtOFP15 transgenic plants were restored to a wild type phenotype by overexpressing ER.On other hand,the double mutant er ofp15 showed a phenotype similar to the er single mutant.These results suggest that ER may functions upstream of AtOFP15 in regulating silique morphology in Arabidopsis.It has been shown that ER function at the upstream of the MAP kinase signaling pathway in regulating plant growth and development,we thus examined whether phosphorylation status of AtOFP15 may affect its function in regulating silique morphology in Arabdopsis.Because the serine(S)or the threonine(T)before the proline in the proteins have been shown to be phosphorylation sites,and the S216 and S219 in AtOFP15 are in a position before proline,thus we taken created point mutations to replace the S amino acids by a alanine(A),or a aspartic acid(D)to generated un-phosphorylated and continue phosphorylated form of AtOFP15,and examined their function in regulating silique morphology by generating transgenic plants overexpressing the mutated AtOFP15.We found that all the transgenic plants obtained showed a wild type phenotype,suggesting that phosphorylation status of the S216 and S219 do not affect AtOFP15's functions in regulating silique morphology.