Plastid Transcription Activity and DNA Copy Number Increase Early in Barley Chloroplast Development

Abstract

Plastid transcription activity and DNA copy number were quantified during chloroplast development in the first foliage leaf in dark-grown and illuminated barley (Hordeum vulgare L.) seedlings. Primary foliage leaves of seedlings given continuous illumination from 2 days post-imbibition reached a final mean length of 15 centimeters at 6.5 days, whereas primary leaves of darkgrown seedlings required 7 days to reach a similar length. Dividing cells were observed in the basal 0.5 to 1 centimeter of primary leaves until 5.5 days post-imbibition. Plastids isolated from cells located in the basal meristem of 4-day-old seedlings were small (-2 micrometers in diameter), exhibited low transcription activity and contained approximately 130 copies of plastid DNA per organelle. Cell size increased from 18 to 60 micrometers in a 1 to 3 centimeter region located adjacent to the leaf basal meristem. In this region, transcriptional activity per plastid increased 10-fold and DNA copy number increased from 130 to 210. Plastid transcriptional activity declined rapidly in illuminated plants with increasing leaf cell age and plastid DNA copy number also declined but with a slower time course. In dark-grown seedlings, plastid transcriptional activity declined more slowly than in illuminated plants while DNA copy number remained constant with increasing cell age. These data show that plastid transcriptional activity and DNA copy number increase early in chloroplast development and that transcriptional activity per DNA template varies up to 5-fold during barley leaf biogenesis.In monocots such as barley or wheat, leaf cells are produced primarily by a meristem located in the leaf base (5). The meristematic cells of the leaf base contain small (1-2 ,um diameter) undifferentiated prochloroplasts (26). In contrast, mesophyll cells located in mature portions of barley leaves contain up to 60 chloroplasts which are 6 to 8 Am in diameter (12,26

Effects of Reduced Chloroplast Gene Copy Number on Chloroplast Gene Expression in Maize

“…3A, left; Supplemental Fig. S2A), in accordance with previous reports that chloroplast DNA copy number decreases modestly in mature chloroplasts, following a maximum early in leaf differentiation (Baumgartner et al, 1989;Zoschke et al, 2007). The ratio of plastid to nuclear gene copy number was estimated for those amplicons whose size and amplification efficiencies were similar to those of the single copy nuclear control (Fig.…”

“…2). Because organelle DNA copy number changes during leaf cell differentiation (Baumgartner et al, 1989;Shaver et al, 2006), we sampled different developmental stages by taking advantage of the developmental gradient in the leaves of maize seedlings (Leech et al, 1973). The second leaf of seedlings at the early three-leaf stage was divided into basal, middle, and apical sections (Fig.…”

“…It is generally agreed that the ratio of chloroplast to nuclear gene copy number decreases as leaf cells mature, although the magnitude of this decrease has been a subject of debate (Baumgartner et al, 1989;Oldenburg and Bendich, 2004a;Rowan et al, 2004;Li et al, 2006;Shaver et al, 2006;Zoschke et al, 2007;Rowan et al, 2009).…”

The Core of Chloroplast Nucleoids Contains Architectural SWIB Domain Proteins

“…If SWIB-4 is indeed functionally related to bacterial architectural proteins, it should influence the shape of chloroplast nucleoids. The structure of plastid nucleoids and DNA topology were proposed to have important consequences for gene expression (Bogorad, 1991;Salvador et al, 1998), which is known to undergo dramatic changes during chloroplast development (Nemoto et al, 1988(Nemoto et al, , 1989Baumgartner et al, 1989;Krupinska and Falk, 1994).…”

Nuclear Mutants of Maize with Defects in Chloroplast Polysome Assembly Have Altered Chloroplast RNA Metabolism

“…During the differentiation of leaf cells, the proplastid differentiates into the much larger, more elongated chloroplast containing the abundant and highly organized thylakoid membrane (reviewed by Mullet, 1988). Accompanying these morphological changes are changes in lipid content (Leech et al, 1973), increases in the abundance of ribosomes and photosynthetic enzymes (reviewed by Mullet, 1988), transient increases in DNA copy number and transcriptional activity (Baumgartner et al, 1989), and an increase in the level of spliced mRNAs relative to their unspliced precursors (Barkan, 1989).…”