BRXTRAFFIC · Plasma membrane to nucleus trafficking of the transcriptional co-activator BRX - characterization of a novel hormone signaling pathway in plants
FP7 — People (Marie Curie Actions)
- Duration
- 2009-09-01 → 2011-08-31
- EU contribution
- €180,801
- Participants
- 1
- Scheme
- MC-IEF
Lines connect the coordinator with its partners.
Results in brief
Plasma membrane to nucleus trafficking of the transcriptional co-activator BRX - characterization of a novel hormone signaling pathway in plants
The focus of the proposed research was to unravel how BRX, a highly conserved plant-specific transcriptional regulator, resides at the plasma membrane and how it is subsequently translocated to the nucleus upon auxin treatment. To investigate this potential novel auxin signaling pathway, we elaborated on the hypothesis that PRAF proteins would be instrumental for BRX localisation and translocation. Nevertheless, by microscopically analyzing transgenic lines, that were established during the first term of the fellowship, localisation of PRAF1 could be clearly demonstrated at the plasma-membrane and in the nucleus thus overlapping with BRX localization. In addition, Bimolecular Fluorescence Complementation (BiFC) assays also indicated that interactions occur between some PRAF family members and some BRX family members, mainly at the level of the plasma-membrane, supporting our initial hypothesis. PRAF proteins however did not follow BRX behaviour: attempts to change the localisation by auxin and/or MG132 treatment were unsuccesful. PRAF proteins possess FYVE and PH domains which are presumably important for membrane trafficking as they are lipid binding domains. However, our experiments could not confirm the importance of these domains for membrane binding as a dominant negative approach in which we mutagenised the PH domain did not change the localisation pattern of the PRAF protein: it was still observed at the PM and occasionally in the nucleus as the WT PRAF protein, in the Col-0 background. Interestengly, in the brx2 background however, a minor change in expression window (i.e. expression appears earlier than compared with the WT) and localisation (i.e. more cytosolic) was noted.
Data: CORDIS, © European Union
Project objective
A major question in biology is how external and internal cues are perceived by the organism and translated into an adequate response at the cellular level. For instance, organ growth in plants involves a phase of cell expansion, which requires extensive rearrangement of cell wall structure and is triggered by systemic cues, such as phytohormones. The complex topic how such cues are interpreted is of major interest in the field of cell biology, which has succeeded in deciphering various intra-cellular signaling pathways. Nevertheless, additional, conceptually different pathways very likely remain to be discovered. A recent example for a conceptually novel pathway is the perception of the phytohormone auxin in the nucleus by direct binding to and regulation of a certain class of E3 ubiquitin ligases, the auxin receptors . Auxin is of pivotal importance in various processes of plant development throughout the life cycle, mainly through its dose-dependent influence on cell proliferation and elongation. In this proposal, we aim to investigate a novel, parallel auxin signaling pathway involving the plant-specific BRX protein that has been recently discovered in the host lab. Unlike the nuclear auxin receptor pathway, this pathway involves plasma membrane to nucleus signaling and responds to alterations in trans-cellular auxin transport, a key phenomenon in plant organogenesis. The aim of this proposal is to solidify the evidence for this pathway and characterize it in more detail to answer two key questions: i) how is BRX, a transcriptional co-activator, targeted to the plasma membrane in a polar fashion? and ii) what is the mechanistic basis for endocytosis-rate and hormone-triggered nuclear import of BRX? We expect that the anticipated results will not only shed light on a novel pathway of pivotal importance in cellular growth of plants, but also conceptually add to our understanding of intra-cellular signaling pathways in general.
Original text from CORDIS.
Participants
- UNIVERSITE DE LAUSANNE · LAUSANNECoordinatorSwitzerland
Links
Data: CORDIS, © European Union