Plant growth and development depends on different signaling pathways. However, there is a degree of interaction between pathways that is being currently studied, especially to uncover molecular mechanisms underlying regulation between hormones. Gibberellin (GA) and brassinosteroids (BRs) regulate common physiological responses, which suggest that here are links between these two hormones, but until now no molecular mechanisms has been proposed.

In this paper the authors show that both hormones act synergistically to promote hypocotyl elongation of light-grown seedlings, but also demonstrated that BRs mediate GA action promoting skotomophogenesis in etiolated seedlings, which suggest also that two pathways do not always act in parallel. In more detail, the article shows that integration of both signaling involves known signaling elements of both pathways. DELLA protein GAI, a major negative regulator of the GA pathway, interact and inactivates BZR1, a transcription factor that broadly regulates gene expression in response to BRs. Since DELLA proteins also are known for bind and regulate PIFs, they propose a model depicting the molecular mechanisms for the integration of GA, BR, and light signaling.

PNAS August 14, 2012. Vol. 109 No. 33