@entity30402 : A Mesophyll Cell-Specific Positive Regulator of Light-Controlled Gene Expression in XXXX .

@entity958 @entity30402 @entity25368 @entity11231
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 @entity11231 ( @entity11231 ) of photosystem II. To understand the mechanism by which light signals nuclear gene expression, we developed a genetic selection to identify mutants with reduced @entity11231 transcription. Here, we describe a new @entity958 locus, @entity30402 (for @entity11231 underexpressed). 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 @entity11231 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, @entity25368 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 @entity11231 expression were unaffected in etiolated @entity30402 seedlings; however, induction of @entity11231 transcription by pulses of red and blue light was reduced, suggesting that @entity30402 acts downstream from both phytochrome and blue light photoreceptors. @entity30402 appears to play a role in the primary derepression of mesophyll-specific gene expression in response to light, because @entity30402 mutants are severely deficient at establishing photoautotrophic growth. Based on this characterization, we propose that @entity30402 is a cell-specific positive regulator linking light and intrinsic developmental programs in @entity958 leaf mesophyll cells.
