MYBL2 is a substrate of GSK2-like kinase BIN2 and acts as a corepressor of BES1 in brassinosteroid signaling pathway in Arabidopsis

The purpose was to understand how BES1, a transcription factor in the BR signaling,  regulates the repression of gene transcription. That is how they found MYBL2, another  transcription factor, that initially was shown to be a direct target of BES1, which repressed it transcriptionally. But further analysis of MYBL2 also demonstrated that could act as a positive regulator on the BR signaling, which was shown in genetic studies with bri1-5 and bes1-D. In addition MYBL2 can bind BES1 (in vitro and in vivo), and apparently together direct the down-regulation of a set of BR-repressed genes. Nevertheless, BIN2 phosphorylation stabilizes MYBL2, which is the opposite to BES1-BZR1, where that leads to their degradation. This dual role of BIN2 phosphorylation raises some questions in the mechanisms of regulation of BR signaling, make it more complex to what we know until now. Is interesting for example to try to reveal why MYBL2 transcription is repressed by BES1 (by BR and in bes1-D), when it is also a positive regulator of the BR pathway. And why a negative regulator as BIN2 stabilizes it.

PNAS vol.109, no.49