HYPERSENSITIVE TO RED AND BLUE 1 and its C‐terminal regulatory function control FLOWERING LOCUS T expression

Abstract

The red and far-red light-absorbing phytochromes and UV-A/blue light-absorbing cryptochromes regulate seedling de-etiolation and flowering responses. The signaling steps that mediate the photoreceptor regulation on key flowering genes remain largely unknown. We report that a previously identified photomorphogenic mutant, hypersensitive to red and blue 1 (hrb1), flowered late and showed attenuated expression of FLOWERING LOCUS T (FT) over both long days and short days. Transgenic plants that overexpress the full-length HRB1, or its C-terminal half, flowered early and accumulated more FT messages under short-day conditions. The transgenic plants also displayed hyposensitive de-etiolation phenotypes, and the expression of these phenotypes requires the action of PIF4. The double mutant of hrb1/cry2 showed a flowering phenotype and an FT expression pattern similar to hrb1 under long-day conditions, suggesting that HRB1 may function downstream of cry2 under long-day conditions. In contrast, hrb1/phyB-9 showed a flowering phenotype and an FT expression pattern similar to phyB-9 over both long days and short days, indicating a modulatory role of HRB1 in the flowering pathway mediated by phyB. Overexpression of HRB1 did not affect the expression of the central clock oscillators, TOC1 and CCA1. HRB1 therefore represents a signaling step that regulates FT expression downstream of red and blue light perception.

An efficient Agrobacterium‐mediated transient transformation of Arabidopsis

“…As a proof of concept, this transient transformation system was used to analyze the subcellular localization of an Arabidopsis protein, HYPERSENSITIVE TO RED AND BLUE 1 (HRB1) (Kang et al. , 2005, 2007).…”

Hypersensitive to Red and Blue 1 and Its Modification by Protein Phosphatase 7 Are Implicated in the Control of Arabidopsis Stomatal Aperture

“…The hypersensitive to red and blue 1 ( hrb1 ) mutant has a short hypocotyl phenotype under red or blue light and a late flowering phenotype [20]–[21]. HRB1 is a small nuclear protein of 23 kDa with an unknown biochemical function [20], but its N-terminal ZZ-type zinc finger motif is likely involved in protein-protein interaction [22].…”

Functional analysis ofTaDi19A, a salt-responsive gene in wheat

“…2006). Although AtDi19‐7/HRB1 appears to regulate phytochrome B mediated red and cryptochrome mediated blue light responses (Kang, Chong & Ni 2005; Kang et al. 2007), the function of the other gene family members has yet to be identified.…”

“…Some of the seven Di19 genes present in A. thaliana are transcriptionally induced by abiotic stress, but not by ABA (Milla et al 2006). Although AtDi19-7/HRB1 appears to regulate phytochrome B mediated red and cryptochrome mediated blue light responses (Kang, Chong & Ni 2005;Kang et al 2007), the function of the other gene family members has yet to be identified.…”