LZF1, a HY5‐regulated transcriptional factor, functions in Arabidopsis de‐etiolation

Abstract

SummaryWe surveyed differential gene expression patterns during early photomorphogenesis in both wild-type and mutant Arabidopsis defective in HY5, an influential positive regulator of the responses of gene expression to a light stimulus, to identify light-responsive genes whose expression was HY5 dependent. These geneexpression data identified light-regulated zinc finger protein 1 (LZF1), a gene encoding a previously uncharacterized C2C2-CO B-box transcriptional regulator. HY5 has positive trans-activating activity toward LZF1 and binding affinity to LZF1 promoter in vivo. HY5 is needed but not sufficient for the induction of LZF1 expression. Anthocyanin content is significantly diminished in lzf1 under far red, which is the most efficient light for the induction of LZF1. The expression of PAP1/MYB75 is elevated in plants overexpressing LZF1, which leads to the hyperaccumulation of anthocyanin in transgenic Arabidopsis. The transition from etioplast to chloroplast and the accumulation of chlorophyll were notably compromised in the lzf1 mutant. We provide molecular evidence that LZF1 influences chloroplast biogenesis and function via regulating genes encoding chloroplast proteins. In the absence of HY5, mutation of LZF1 leads to further reduced light sensitivity for lightregulated inhibition of hypocotyl elongation and anthocyanin and chlorophyll accumulation. Our data indicate that LZF1 is a positive regulator functioning in Arabidopsis de-etiolation.

BBX32, an Arabidopsis B-Box Protein, Functions in Light Signaling by Suppressing HY5-Regulated Gene Expression and Interacting with STH2/BBX21

“…Previous studies have shown that several B-box proteins, including STH2 and LZF1 (STH3), which both directly interact with HY5, play roles in light signaling (Datta et al, 2007(Datta et al, , 2008Chang et al, 2008;Kumagai et al, 2008). Despite extensive efforts, we did not detect any direct interaction between BBX32 and HY5, nor did we find an interaction of BBX32 with DNA.…”

“…HY5 is known to interact with other B-box proteins like STH2/BBX21 and LZF1/STH3/BBX22, which function positively in light signaling with HY5; null mutations in STH2/BBX21 and LZF1/STH3/BBX22 genes cause phenotypes similar to the hy5 mutants (Datta et al, 2007(Datta et al, , 2008Chang et al, 2008). BBX32 might either directly interact with HY5 and/or bind one or more of the other B-box proteins that interact with HY5.…”

“…STH2/ BBX21 and LZF1/STH3/BBX22 are positive regulators of red, far-red, and blue light signaling. They physically interact with HY5 through the B-box motifs, promote anthocyanin accumulation in concert with HY5, and LZF1/STH3/BBX22 was shown to be ubiquitinated by COP1 (Datta et al, 2007(Datta et al, , 2008Chang et al, 2008). Some other double B-box proteins, DBB1a/ BBX18, DBB1b/BBX19, and STO/BBX24, have been shown to function negatively in light signaling (Indorf et al, 2007;Kumagai et al, 2008;Khanna et al, 2009).…”

“…CO acts as a positive regulator of the floral transition in response to inductive photoperiods, whereas COL3 has been shown to act as a positive regulator of red light signaling (Putterill et al, 1995;Datta et al, 2006). Both CO and COL3 proteins contain two N-terminal B-box motifs and a CCT (for CO, CO-LIKE, TOC) domain in the C terminus (Wenkel et al, 2006;Chang et al, 2008;Khanna et al, 2009). Several other B-box proteins have been implicated in light-regulated development.…”

“…Several other B-box proteins have been implicated in light-regulated development. STH2/BBX21 and LZF1/STH3/BBX22 contain two B-box motifs in the N terminus but lack the CCT domain (Datta et al, 2007(Datta et al, , 2008Chang et al, 2008;Kumagai et al, 2008;Khanna et al, 2009). STH2/ BBX21 and LZF1/STH3/BBX22 are positive regulators of red, far-red, and blue light signaling.…”