C-5-1 - Using chimeric constitutive activators and repressors to define HY5 transcription activity in Arabidopsis
Sunday, July 15
1:03 PM - 1:23 PM
Yogev Burko, PhD
The Salk Institute for Biological Studies, Howard Hughes Medical Institute
The Arabidopsis transcription factor HY5 plays an important role during many plant developmental processes such as root growth, temperature response and flowering time, as well as the transition from the etiolated (dark-grown), to de-etiolated (post light exposure) growth program. While all reports agree that HY5 works downstream of the photoreceptors to control gene expression, they are divided on whether HY5 works primarily by activating or repressing expression of its direct target genes. In this study we aim to determine the dominant activity of HY5 during de-etiolation and relate this to other HY5 dependent phenotypes. To this end, we generated dominant repressor and dominant activator HY5 fusion proteins (HY5-SRDX and HY5-VP16, respectively), to control the expression of HY5 target genes. We confirmed their activity and compared these lines with HY5 overexpression (HY5ox) and the hy5 loss of function mutant by RNA-seq, ChIP-seq and multiple phenotypes to determinate the dominant activity of HY5. These data combined demonstrate that HY5 acts primarily as an activator of gene expression at the molecular level. This activity is reflected in the phenotypes observed under all conditions tested. These data allow us to identify high confidence direct targets of HY5. Unexpectedly, we found that HY5-VP16 had a partial de-etiolation phenotype when grown in the dark, suggesting that HY5 works in an activation complex that requires light. Lastly, we expressed HY5-VP16 and HY5-SRDX in tomato plants as proof of concept that we can use these fusion proteins to modulate growth in crop plants. We suggest that this strategy can be used to define the transcription regulation activity and direct targets of other transcription factors for which there is a debate. Future studies are directed toward identifying members of HY5 complexes that are required to activate its direct targets.
Mark Zander – The Salk Institute for Biological Studie, Howard Hughes Medical Institute; Joseph Ecker – The Salk Institute for Biological Studie, Howard Hughes Medical Institute; Joanne Chory – The Salk Institute for Biological Studie, Howard Hughes Medical Institute