Developmentally regulated expression of the BRI1 brassinosteroid receptor in Arabidopsis thaliana

Brassinosteroids (BRs) are important regulators of morphogenic events during plant development. The lack of active transport and well-characterized biosynthesis offer ideal conditions for studying the local and temporal effects of this hormone group. While recent studies have found clear coincidence between the sites of BR accumulation and organ differentiation, they have also provided evidence for developmental changes in hormone susceptibility. In order to investigate the role of the BR receptor BRI1 in the modulation of hormone sensitivity, we studied the time course and localization of BRI1 gene activity in Arabidopsis seedlings. To this end, we generated transgenic lines carrying BRI1 promoter-driven luciferase or GUS reporter genes and characterized the expression patterns of these chimeric genes. Our results showed increased BRI1 expression in dark grown seedlings, particularly in the elongation zone of the hypocotyl, and also at the sites of organ development in green seedlings. These data indicate that, in addition to local increases in the hormone level, the abundance of the receptor can also be instrumental in eliciting the BR response

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

Timothy syndrome 1 genotype without syndactyly and major extracardiac manifestations.

Timothy syndrome 1 (TS1) is a rare genetic disorder characterized by multisystem abnormalities including QT prolongation, congenital heart defects, facial dysmorphism, episodic hypoglycemia, and neurological symptoms. A morphological hallmark of TS1 is syndactyly, present in all cases. TS1 is caused by the canonical p.Gly406Arg mutation in the alternatively spliced exon 8A in the CACNA1C gene, encoding for the main cardiac L-type calcium channel. A variant case of TS1 is reported. The proband had intermittent fetal bradycardia with heart rate of 72 bpm. On the first day of life bradycardia due to 2:1 atrioventricular (AV) block and marked QTc prolongation of 600 ms was noted. On medical therapy with propranolol and mexiletine 1:1 AV conduction returned with QTc prolongation of 470-580 ms. The patient lacked other extracardiac manifestations, most importantly syndactyly, neurological complications or autism. On genetic analysis, the canonical TS1 causing mutation, p.Gly406Arg in exon 8A of the CACNA1C gene was detected. The CACNA1C p.Gly406Arg variant was not present in the parents, but was detected in different DNA samples of the index patient. Our case highlight further phenotypic variability in TS. Most importantly, it underlines that the lack of syndactyly does not exclude the presence of a TS1 genotype. (c) 2017 Wiley Periodicals, Inc