AtMYB44 suppresses transcription of the late embryogenesis abundant protein gene AtLEA4-5.

AtLEA4-5 is a member of the group 4 late embryogenesis abundant (LEA) proteins, which are involved in the tolerance of water deficit in Arabidopsis thaliana. Chromatin immunoprecipitation assays revealed that the transcription factor AtMYB44 bound directly to the AtLEA4-5 gene promoter region under normal conditions, but was eliminated in response to osmotic stress (mannitol treatment). A quantitative reverse transcription PCR assay revealed that transcription of the AtLEA4-5 gene was induced in response to either salt (salinity) or mannitol (osmosis) treatment. The abiotic stress-induced increase in AtLEA4-5 transcripts was reduced in 35S:AtMYB44 transgenic plants, indicating that the transcription factor AtMYB44 represses gene transcription. More RNA polymerase II stalled at the transcription start site (TSS) of the AtLEA4-5 gene loci under osmotic stress, but the increment was reduced in the 35S:AtMYB44 plants. Histones are evicted from the promoter region under osmotic stress; however, histone eviction was hampered in the 35S:AtMYB44 plants. Under osmotic stress, the acetylated histones remaining at the TSS region was significantly lower in the 35S:AtMYB44 plants compared with wild-type plants. These results indicate that AtMYB44 suppresses polymerase-mediated transcription of the AtLEA4-5.