DBB1a, involved in gibberellin homeostasis, functions as a negative regulator of blue light-mediated hypocotyl elongation in Arabidopsis

Abstract

Double B-box 1a (DBB1a) belongs to the zinc-finger family proteins in Arabidopsis thaliana. Transcriptional analysis uncovered that the DBB1a gene expression was blue light-dependently regulated, and the transcript level of DBB1a in cry1cry2 was decreased but not in phyAphyB compared to wild type under blue light conditions. Transgenic plants containing pDBB1a:GUS (β-glucuronidase) displayed GUS activity in the vascular system of leaves and petioles. Green fluorescent protein (GFP)-fused DDB1a (DBB1a-GFP) protein was found in the nucleus in transient transformation assays with onion epidermal cells as well as in stable transgenic Arabidopsis plants. To investigate the function of DBB1a, we generated DBB1a over-expressing and under-expressing transgenic Arabidopsis plants. Analysis of hypocotyl growth of these lines indicated that DBB1a promoted hypocotyl elongation under blue light condition. The phenotype of transgenic plants with DBB1a over-expression could be impaired by a gibberellin (GA)-biosynthesis inhibitor. Moreover, the expression analysis of GA metabolic and catabolic genes in DBB1a transgenic lines indicated that the DBB1a suppressed GA2-oxidase1 (GA2ox1) and GA2-oxidase8 (GA2ox8) expression, but induced GA3β-hydroxygenase1 (GA3ox1) and GA20-oxidase1 (GA20ox1) expression under blue light. Taken together, we concluded that DBB1a promotes hypocotyl elongation under blue light condition through an increase in bioactive GA levels in Arabidopsis.

The BBX subfamily IV

“…Light fluence-response analyses of BBX18 gain-and-loss-of-function lines proved that this gene is involved in blue light-dependent hypocotyl elongation as a negative regulator, and its phenotype is related to gibberellin signaling pathways. 65 Further experiments have proved that BBX18 is involved as a negative regulator of basal and acquired thermotolerance. 66 In addition, BBX18 has been related to flower development.…”

“…39 The expression of both transcripts is regulated by the circadian rhythm, and 35S:BBX18 and 35S:BBX19 overexpression plants display hyposensitivity to red and far-red light. Experiments by Wang and colleagues 65 demonstrated that BBX18 is a nuclear-localized protein. Light fluence-response analyses of BBX18 gain-and-loss-of-function lines proved that this gene is involved in blue light-dependent hypocotyl elongation as a negative regulator, and its phenotype is related to gibberellin signaling pathways.…”

“…65,71 Independent experiments demonstrate that BBX21, BBX22 and BBX24 have transactivating capacity in transcriptional systems, 44,45,51,60 although no DNA binding ability has been described. The proposed mechanism of action uses the interaction with other transcription factors that bind to DNA, such as HY5 and HYH (Fig.…”

Light-Responsive Double B-Box Containing Transcription Factors Are Conserved inPhyscomitrella patens

“…[13][14][15] AtBBX18/DBB1a is involved in gibberellin homeostasis and the regulation of hypocotyl elongation in response to blue light. 16) Interestingly, AtBBX21/ STH2 and AtBBX22/STH3/LZF1 appear to be targets of COP1. 14,15) Based on knowledge from the seed plant A. thaliana, here we asked a fundamental question as to whether BBX-IV homologues are conserved in P. patens.…”

“…AtBBX18/DBB1a is primarily responsive to blue light and AtBBX22/STH3/LZF1 to far-red light. 16,17) It is suggested, apart from regulatory mechanism, the property of light induction in PpBBX-IVg expression is conserved in P. patens. Here, another critical question is whether expression of them is subject to the diurnal oscillation in light and dark cycles, because it is known that most AtBBX-IV members, including AtBBX18 and AtBBX24, are under the control of the circadian clock.…”