Target genes and regulatory domains of the GAMYB transcriptional activatorin cereal aleurone

GAMYB is an MYB transcription factor which is expressed in cereal aleurone cells in response to gibberellin (GA). HvGAMYB binds to the TAACAAA box of a high-pI alpha-amylase gene promoter and transcriptionally activates its e xpression. In this study, we examined the role of HvGAMYB in activating exp ression of other GA-regulated genes encoding hydrolytic enzymes. In transie nt expression experiments, HvGAMYB transactivated expression of reporter ge nes fused to a low-pI alpha-amylase gene promoter, an EII(1-3,1-4)-beta-glu canase gene promoter and a cathepsin B-like protease promoter. HvGAMYB DNA binding specificity was determined using a PCR-based random site selection using HvGAMYB fusion protein isolated from E. coli. The deduced consensus c losely resembled gibberellin response elements in alpha-amylase promoters. Functional analysis of HvGAMYB by transient expression of C terminal HvGAMY B deletions in barley aleurone cells identified two transcriptional activat ion domains (TADs) which function in transcriptional regulation of both hig h- and low-pI alpha-amylase promoters. The same TADs were identified using a heterologous yeast expression system. Together, these results indicate th at HvGAMYB has two TADs. These domains are C-terminal to its DNA-binding do main.