The Function Analysis Of BZR1-interacting Protein BIP1 In Arabidopsis Thaliana

Brassinosteroid (BR) is a kind of essential phytohormone, participates in the regulation of plant growth and development process as well as the response to the biotic and abiotic stress. Research on the BR signal’s transduction have important scientific significance. BZR1 is the key transcription factor of BR signal, however, the molecular mechanism of how BZR1 regulates it’s down-stream target genes remains largely unknown.In this study, we attempt to analysis the molecular mechanism of BZR1’s transcription function through screening and identifying it’s interacting protein. Through yeast-two-hybridization assay(Y2H), we identified a protein that can direct interact with BZR1, and we named it BZR1 Interacting Protein 1(BIP1). The Luciferase Complementary Imaging assay(LCI) and the Bimolecular Fluorescence complementation assay(BiFC) also indicate that BIP1 can directly interact with BZR1.We constructed the binary vector 35S::BIP1-GFP to test the subcellular localization of BIP1 protein and found that BIP1 mainly locate in the cytoplasm. However, when we co-expressed BIP1 with BZR1, the subcellular localization of BIP1 changed. We can find the GFP signal both in the cytoplasm and the nucleus. This result implies that BIP1 can shuttle between the cytoplasm and the nucleus, and this process may rely on the existence of BZR1.We then make a study on the BIP1 T-DNA insert mutant line bipl-1. We found that bipl-1 shows typical photomorphogenesis phenotype in dark growth condition, with a shorter hypocotyl and opened cotyledons. These phenotypes are similar to the BR biosynthesis deficient mutant det2 and BR insensitive mutant bin2. We then construct the genetic material bipl-1/bzrl-1D and bipl-1135s::BZR1-7Myc-6 His through hybridization, and we find that BIP can significantly repress their phenotype of longer hypocotyl. This results indicate that BZR1’s function may at least partially depend on BIP1.The qRT-PCR data reveals that BZR1 target genes’expression, like PRE1 and SAUR-AC, were remarkablely reduced in bipl-1 mutant compared with the wild-type Col-0. However,the light-signal downstream transcription factors’ expression, like GATA2 and GATA4, were dramatically induced in bipl-1. this results were in corelate with the shorter hypocotyl and opened cotyledons mutant phenotype. These data reveal that BIP1 may involved in the BZR1-depended photomorphogenesis process.In conclusion, BIP1 can physically interact with the BR signal’s core transcription factor BZR1 and co-regulate the photomorphogenesis process related genes’ expression. This research have a great importance of further understand of how the BZR1 operate it’s function as an important transcription factor, and controls downstream genes expression.