2024-03-29T09:02:14Zhttp://digital.csic.es/dspace-oai/requestoai:digital.csic.es:10261/188272016-02-16T06:04:11Zcom_10261_103com_10261_1col_10261_860
Abscisic acid signal transduction: Regulation by HAB1 and interaction with brassinosteroids mediated by BRX
Rodrigues, Americo do Patrocinio
Rodriguez Egea, Pedro
Ácido abscísico
Brasinoesteroides
Arabidopsis
HAB1
Tesis doctoral del Departamento de Biotecnología de la Universidad Politécnica de Valencia, realizada en el Instituto de Biología Molecular y Celular de Plantas
The phytohormone abscisic acid (ABA) is a key regulator of plant growth and
development as well as of plant responses to stress namely water and salt stresses.
To gain further insight into ABA signaling and its role in growth regulation, we
have screened for Arabidopsis thaliana mutants hypersensitive to ABA-mediated root
growth inhibition. In this screen, we have identified a loss-of-function allele of BREVIS
RADIX (BRX) in Columbia background, named brx-2. BRX encodes a key regulator of
cell proliferation and elongation in the root, which has been implicated in the
brassinosteroid (BR) pathway as well as regulation of auxin-responsive gene
expression. Mutants affected in BR signaling that are not impaired in root growth, such
as bes1-D, bzr1-D and bsu1-D, also showed enhanced sensitivity to ABA-mediated
inhibition of root growth. Triple loss-of-function mutants affected in protein
phosphatases type-2C (PP2Cs) that act as negative regulators of ABA signaling
showed impaired root growth in the absence of exogenous ABA, indicating that
disturbed regulation of ABA sensitivity impairs root growth. In agreement with this
result, diminishing ABA-sensitivity of brx-2 by crossing it with a 35S:HAB1 ABAinsensitive
line allowed significantly higher recovery of root growth after BL treatment.
Finally, transcriptomic analysis revealed that ABA treatment negatively affects auxin
signaling in wild type and brx-2 roots and that ABA response is globally altered in brx-2.
Taken together, our results reveal an interaction between BRs, auxin and ABA in the
control of root growth and indicate that fine tuning of ABA response might be required
to prevent a deleterious effect on growth and development in the absence of
environmental stress. ABA response is controlled by a complex network in which
phosphorylation/dephosphorylation events have a very important role. HAB1 is a PP2C
that plays a key role as negative regulator of ABA signaling; however, the molecular
details of HAB1 action in this process are not known. A two hybrid screening revealed
that AtSWI3B, an Arabidopsis homolog of the yeast SWI3 subunit of SWI/SNF
chromatin remodeling complexes, is a prevalent interacting partner of HAB1. The
interaction mapped to the N-terminal half of AtSWI3B and required an intact protein
phosphatase catalytic domain. Bimolecular fluorescence complementation (BiFC) and
coimmunoprecipitation (ChIP) assays confirmed the interaction of HAB1 and SWI3B in
the nucleus of plant cells. Yeast two hybrid and BiFC assays also confirmed the
interaction of SWI3B with ABI1, ABI2 and PP2CA, though this interaction was weaker
than the observed with HAB1. swi3b mutants showed a reduced sensitivity to ABA mediated inhibition of seed germination and growth, and reduced expression of the
ABA-responsive genes RAB18 and RD29B. ChIP experiments showed that the
presence of HAB1 in the vicinity of RD29B and RAB18 promoters was abolished by
ABA, which suggests a direct involvement of HAB1 in regulation of ABA-induced
transcription. Contrary to the phenotypes presented by swi3b mutants, mutants of BRM
and SYD, other putative members of Arabidopsis SWI/SNF complex, showed
hypersensitivity to ABA in germination, root growth and enhanced expression of ABA
responsive genes. Additionally, our results uncover AtSWI3B as a novel positive
regulator of ABA signaling and suggest that HAB1 modulates ABA response through
regulation of a putative SWI/SNF chromatin remodelling complex.
2009-11-19T13:49:18Z
2009-11-19T13:49:18Z
2009
tesis doctoral
http://hdl.handle.net/10261/18827
eng
openAccess
Universidad Politécnica de Valencia