CUE1: A Mesophyll Cell-Specific Positive Regulator of Light-Controlled Gene Expression in Arabidopsis.

Abstract

Light plays a key role in the development and physiology of plants. One of the most profound effects of light on plant development is the derepression of expression of an array of light-responsive genes, including the genes encoding the chlorophyll alb binding proteins (CAB) of photosystem II. To understand the mechanism by which light signals nuclear gene expression, we developed a genetic selection to identify mutants with reduced CAB transcription. Here, we describe a new Arabidopsis locus, COE7 (for CAS ynderexpressed). Mutations at this locus result in defects in expression of several light-regulated genes, specifically in mesophyll but not in bundle-associated or epidermis cells. Reduced accumulation of CAB and other photosynthesis-related mRNAs in the mesophyll was correlated with defects in chloroplast development in these cells, resulting in a reticulate pattern with veins greener than the interveinal regions of leaves.Moreover, chalcone synthase mRNA, although known to be regulated by both phytochrome and a blue light receptor, accumulated normally in the leaf epidermis. Dark basal levels of CAB expression were unaffected in etiolated cueí seedlings; however, induction of CAB transcription by pulses of red and blue light was reduced, suggesting that CUEl acts downstream from both phytochrome and blue light photoreceptors. CUEl appears to play a role in the primary derepression of mesophyll-specific gene expression in response to light, because cueí mutants are severely deficient at establishing photoautotrophic growth. Based on this characterization, we propose that CUEí is a cell-specific positive regulator linking light and intrinsic developmental programs in Arabidopsis leaf mesophyll cells.

Mutations Affecting Induction of Glycolytic and Fermentative Genes during Germination and Environmental Stresses in Arabidopsis1

“…Characterization of three of these regulatory mutants has provided us with information for understanding the molecular mechanism of induction of ADH and PDC1 genes by three different environmental stresses. Li et al (1995) used a similar screening scheme successfully to isolate trans-regulatory mutants of the CAB gene in Arabidopsis.…”

An Arabidopsis Mutant Hypersensitive to Red and Far-Red Light Signals

“…Mutants impaired in far-red light perception but not in phytochrome A levels ( fhy1 and fhy3 ; Whitelam et al, 1993) seem to lack functional proteins involved in regulating secondary branches of the phyA signal transduction pathway. In addition, the cue1 mutation of Arabidopsis (Li et al, 1995) has been implicated in the regulation of plastid development and light-responsive gene expression, and the DOC gene product is hypothesized to be a repressor of chlorophyll a / b binding protein ( CAB ) genes in the dark (Li et al,1994). Recently, Wagner et al (1997) described a putative signal transduction mutant, red1 , that appears to be specific to the phyB pathway.…”

S2F, a leaf-specific trans-acting factor, binds to a novel cis-acting element and differentially activates the RPL21 gene.

“…However, little is known about the cis-and trans-acting factors responsible for the tissue-specific expression of these genes because no clear separation of light-responsive and tissue-specific cis elements was possible (Gilmartin et al, 1990 4T0 whom correspondence should be addressed. E-mail regismache @ujf-grenoble.fr; fax 33-47651 -4336. lowed the identification of a mesophyll cell regulatory gene, CUE7, establishing a link between light and cell-specific activation of photosynthetic genes (Li et al, 1995). Analysis of the photomorphogenic Arabidopsis deetiolated det7 and constitutive photomorphogenic copl mutants indicates that root cells of these mutants contain chloroplasts that are partially differentiated and accumulate significant amounts of light-regulated mRNAs (Chory et al, 1989).…”