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"Scaffold-mediated Assembly of the Brassinosteroid Signaling Components by TTL proteins"

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Thursday 30 June 2016, 11:00 - 12:30


Brassinosteroids (BRs) is a group of plant steroidal hormones that play critical roles in multiple aspects of plant growth and development. BR signal is transduced from receptor kinases at the cell surface to the nucleus through well-characterized kinases and phosphatases, leading to dephosphorylation and nuclear re-localization of the key transcription factors BES1 and BZR1. Previous studies show that all these components associate forming an autonomous interconnected signaling pathway, although it is not known how these proteins are brought together for transducing BR signaling. We report that the plant-specific Tetratricopeptide Thioredoxin-Like TTL proteins function as a scaffold of the BR pathway in Arabidopsis. TTL3 interacts with all core components involved in transducing BR signaling (BRI1, BSK1, BSU1, BIN2 and BZR1). Consistent with this role, a triple ttl1/ttl3/ttl4 of the most expressed TTL genes shows acute defects in BRs responses. We also show that a functional TTL3-green fluorescence protein is mainly localized in the cytoplasm and that BR causes a rapid association to the plasma membrane. We propose a novel mechanistic model for BR signaling, in which cytoplasmic components bound to TTL proteins are translocated from the cytoplasm to the plasma membrane upon BR perception, which in turn allow the formation of a complete BR signaling complex with the goal of ensuring TF de-phosphorylation and nuclear accumulation of the transcription factors. Interestingly, this novel model for BR signaling strongly resemble that of Wnt signaling in which TTL proteins would act as Axin1 by regulating assembly and disassembly of a functional complex.

Location Jozef Schell seminar room
Contact Prof Miguel Angel Botella
The Institute for Mediterranean and Subtropical Horticulture (IHSM-UMA-CSIC)
Department of Molecular Biology and Biochemistry
University of Málaga