18 research outputs found
The Arabidopsis thaliana Brassinosteroid Receptor (AtBRI1) Contains a Domain that Functions as a Guanylyl Cyclase In Vitro
BACKGROUND: Guanylyl cyclases (GCs) catalyze the formation of the second messenger guanosine 3′,5′-cyclic monophosphate (cGMP) from guanosine 5′-triphosphate (GTP). Cyclic GMP has been implicated in an increasing number of plant processes, including responses to abiotic stresses such as dehydration and salt, as well as hormones. PRINCIPLE FINDINGS: Here we used a rational search strategy based on conserved and functionally assigned residues in the catalytic centre of annotated GCs to identify candidate GCs in Arabidopsis thaliana and show that one of the candidates is the brassinosteroid receptor AtBR1, a leucine rich repeat receptor like kinase. We have cloned and expressed a 114 amino acid recombinant protein (AtBR1-GC) that harbours the putative catalytic domain, and demonstrate that this molecule can convert GTP to cGMP in vitro. CONCLUSIONS: Our results suggest that AtBR1 may belong to a novel class of GCs that contains both a cytosolic kinase and GC domain, and thus have a domain organisation that is not dissimilar to that of atrial natriuretic peptide receptors, NPR1 and NPR2. The findings also suggest that cGMP may have a role as a second messenger in brassinosteroid signalling. In addition, it is conceivable that other proteins containing the extended GC search motif may also have catalytic activity, thus implying that a significant number of GCs, both in plants and animals, remain to be discovered, and this is in keeping with the fact that the single cellular green alga Chlamydomonas reinhardtii contains over 90 annotated putative CGs
Differential expression of the brassinosteroid receptor-encoding BRI1 gene in Arabidopsis
Abstract Brassinosteroid (BR)-regulated growth and
development in Arabidopsis depends on BRASSINOSTEROID
INSENSITIVE 1 (BRI1), the BR receptor that
is responsible for initiating the events of BR signalling.
We analysed the temporal and spatial regulation of BRI1
expression using stable transgenic lines that carried BRI1
promoter:reporter fusions. In both seedlings and mature
plants the tissues undergoing elongation or differentiation
showed elevated BRI1 gene activity, and it could be
demonstrated that in the hypocotyl this was accompanied
by accumulation of the BRI1 transcript and its receptor
protein product. In seedlings the BRI1 promoter was also
found to be under diurnal regulation, determined primarily
by light repression and a superimposed circadian control.
To determine the functional importance of transcriptional
regulation we complemented the severely BR insensitive
bri1-101 mutant with a BRI1-luciferase fusion construct
that was driven by promoters with contrasting specificities.
Whereas the BRI1 promoter-driven transgene fully restored the wild phenotype, expression from the photosynthesisassociated
CAB3 and the vasculature-specific SUC2 and
ATHB8 promoters resulted in plants with varying morphogenic
defects. Our results reveal complex differential regulation
of BRI1 expression, and suggest that by influencing
the distribution and abundance of the receptor this regulation
can enhance or attenuate BR signalling