Poster: Intracellular Signaling

Abs # 840: An Arabidopsis Protein with Sequence Similarity to Animal TGF-beta Receptor Interacting Protein is Phosphorylated by the BRI1 Receptor Kinase in vitro.

Presenter:	Ehsan, Hashimul , hehsan@unity.ncsu.edu
Authors	Ehsan, Hashimul  (A)   Ray, William K. (B)   Huber, Steven C. (A)   Clouse, Steven D. (A)
Affiliations:	(A): North Carolina State University (B): Michigan State University

Brassinosteroids (BRs) regulate the expression of numerous genes associated with plant development and require the activity of BRI1, a Ser/Thr receptor kinase, to realize their effects. The Transforming Growth Factor-beta (TGF-beta) family of peptides, acts via Ser/Thr receptor kinases to prominently impact several pathways involved in animal development and adult homeostasis. In animals, TGF-beta Receptor Interacting Protein (TRIP-1) is an intracellular substrate of the TGF-beta Type II receptor kinase and plays an important role in TGF-beta signaling. We recently found that transcript levels of TRIP-1 homologs in plants are regulated by BR treatment under a variety of conditions, and that transgenic plants expressing antisense TRIP-1 RNA exhibit a broad range of developmental defects including some that resemble the phenotype of BR-deficient and –insensitive mutants. Furthermore, we have shown that recombinant BRI1 kinase domain phosphorylates recombinant TRIP-1 in vitro. These findings suggest that TRIP-1 may mediate some of the molecular mechanisms underlying the regulation of plant growth and development by BRs, possibly as a direct substrate of the BRI1 receptor kinase. We have identified three Thr residues in TRIP-1 that are the putative targets of BRI1 phosphorylation, using MALDI and Q-TOF mass spectrometry. Immunoprecipitation followed by mass spectrometry is also being used to identify in vivo phosphorylation sites of TRIP-1 and their possible dependence on an active BRI1 receptor kinase.