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Light provides crucial positional information in plant development, and the morphogenetic processes that are orchestrated by light signals are triggered by changes of gene expression in response to variations in light parameters. Control of expression of members of the RbcS and Lhc families of photosynthesis-associated nuclear genes by light cues is a paradigm for lightregulated gene transcription, but high-resolution expression profiles for these gene families are lacking. In this study, we have investigated expression patterns of members of the RbcS and Lhc gene families in Arabidopsis (Arabidopsis thaliana) at the cellular level during undisturbed development and upon controlled interference of the light environment. Members of the RbcS and Lhc gene families are expressed in specialized territories, including root tip, leaf adaxial, abaxial, and epidermal domains, and with distinct chronologies, identifying successive stages of leaf mesophyll ontogeny. Defined spatial and temporal overlap of gene expression fields suggest that the light-harvesting and photosynthetic apparatus may have a different polypeptide composition in different cells and that such composition could change over time even within the same cell.
Plants are exquisitely sensitive to their light environment and have evolved sophisticated biochemical systems to perceive intensity, quality, direction, and duration of the light signal (Chen et al., 2004). Information regarding these parameters is used to modulate an amazing variety of developmental processes throughout the plant's life, thus defining light as one of the most important cues in plant development (Fankhauser and Chory, 1997; Franklin et al., 2005). Most of the events choreographed by light require changes in gene expression (Simpson and Herrera- Estrella, 1990; Thompson and White, 1991), and regulation of gene expression by light, particularly that of the genes encoding the small subunits of the Rubisco (RbcS) and the light-harvesting chlorophyll a/b-binding proteins (Lhc; previously known as Cab), has been the subject of extensive investigation (Arguello-Astorga and Herrera-Estrella, 1998).
The enzyme Rubisco is located in the stroma of the chloroplast, where it catalyzes the carboxylation of ribulose bisphosphate in the Calvin cycle and the oxygenation of the same substrate in the photorespiratory pathway (Jensen and Bahr, 1977). Rubisco is a multimeric enzyme consisting of eight small subunits and eight large subunits (Baker et al., 1975), and while the large subunits are encoded by a single chloroplast gene...