25.07.2012

<strong>ZMBP Special Seminar</strong> Friday, July 27 10:00 Uhr, Zhiyong Wang Carnegie Institution/Stanford University USA

"Brassinosteroid, gibberellin, and light signaling pathways impinge on a central network controlling photomorphogenesis."

Hörsaal N11, Auf der Morgenstelle 3

Abstract
Plant development is controlled by multiple environmental signals and endogenous hormones. The
molecular mechanisms of signalling integration remain largely unknown. One of the best examples
of signal coregulation is the regulation of photomorphogenesis by light, brassinosteroid (BR), and
gibberellic acid (GA). These signals have similar (or opposite) effects on the same cellular and
developmental responses, but act through distinct signalling pathways, which have all been
characterized in detail. But how the BR-signaling pathway is integrated with the light- and GAsignaling
pathways has remained an outstanding question. Contrary to the traditional thoughts that
environmental signals regulate growth by changing the hormone level or sensitivity, there has been
no evidence for light regulation of BR synthesis or signalling. Instead, we found that BR activation of
the BZR1 transcription factor represses the expression levels of many components of the lightsignalling
network, including photoreceptors and light-stabilized transcription factors. Furthermore,
we provide genetic, genomic, and biochemical evidence showing that BZR1 and phytochromeinteracting
factor 4 (PIF4) interact with each other, and interdependently mediate gene-expression
and cell-elongation responses to BR, dark, shade, and high temperature. The activity of the BZR1-
PIF4 complex is, however, inhibited by the GA-inactivated DELLA proteins, which bind to and inhibit
DNA binding of both PIFs and BZR1. As such, the BZR1-PIF4-DELLA trio integrates multiple
signalling pathways into a central transcription network that controls the developmental switch
between etiolation and de-etiolation.