Abstract
BackgroundChloroplasts are the green plastids where photosynthesis takes place. The biogenesis of chloroplasts requires the coordinate expression of both nuclear and chloroplast genes and is regulated by developmental and environmental signals. Despite extensive studies of this process, the genetic basis and the regulatory control of chloroplast biogenesis and development remain to be elucidated.ResultsGreen cauliflower mutant causes ectopic development of chloroplasts in the curd tissue of the plant, turning the otherwise white curd green. To investigate the transcriptional control of chloroplast development, we compared gene expression between green and white curds using the RNA-seq approach. Deep sequencing produced over 15 million reads with lengths of 86 base pairs from each cDNA library. A total of 7,155 genes were found to exhibit at least 3-fold changes in expression between green and white curds. These included light-regulated genes, genes encoding chloroplast constituents, and genes involved in chlorophyll biosynthesis. Moreover, we discovered that the cauliflower ELONGATED HYPOCOTYL5 (BoHY5) was expressed higher in green curds than white curds and that 2616 HY5-targeted genes, including 1600 up-regulated genes and 1016 down-regulated genes, were differently expressed in green in comparison to white curd tissue. All these 1600 up-regulated genes were HY5-targeted genes in the light.ConclusionsThe genome-wide profiling of gene expression by RNA-seq in green curds led to the identification of large numbers of genes associated with chloroplast development, and suggested the role of regulatory genes in the high hierarchy of light signaling pathways in mediating the ectopic chloroplast development in the green curd cauliflower mutant.
Highlights
Chloroplasts are the green plastids where photosynthesis takes place
The green curd cauliflower mutant serves as an excellent model system for investigating the genetic basis of chloroplast biogenesis in plants
Many genes involved in chlorophyll biosynthesis were found to be expressed highly in green curd in comparison with white (Figure 3)
Summary
Chloroplasts are the green plastids where photosynthesis takes place. The biogenesis of chloroplasts requires the coordinate expression of both nuclear and chloroplast genes and is regulated by developmental and environmental signals. Chloroplast biogenesis from proplastids requires coordinate expression of nuclear and chloroplast genes [1], and is largely regulated by developmental and environmental cues such as light. 3000 proteins in chloroplasts are encoded by the nucleus [2] They participate in a large number of functional processes that are required for chloroplast biogenesis. These processes include import of nuclear encoded proteins through the Toc/Tic complexes, protein assembly and disassembly with chaperone proteins, thylakoid formation, pigment synthesis, plastid divisions, and retrograde been genetically characterized as a positive regulator of photomorphogenesis under a broad spectrum of light and affects chloroplast development [4,11]. Determining how these genes are coordinately expressed during chloroplast development requires a genome-wide examination of gene expression during the transition from non-colored plastids into chloroplasts
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