Loss or retention of chloroplast DNA in maize seedlings is affected by both light and genotype

Abstract

We examined the chloroplast DNA (cpDNA) from plastids obtained from wild type maize (Zea mays L.) seedlings grown under different light conditions and from photosynthetic mutants grown under white light. The cpDNA was evaluated by real-time quantitative PCR, quantitative DNA fluorescence, and blot-hybridization following pulsed-field gel electrophoresis. The amount of DNA per plastid in light-grown seedlings declines greatly from stalk to leaf blade during proplastid-to-chloroplast development, and this decline is due to cpDNA degradation. In contrast, during proplastid-to-etioplast development in the dark, the cpDNA levels increase from the stalk to the blade. Our results suggest that DNA replication continues in the etioplasts of the upper regions of the stalk and in the leaves. The cpDNA level decreases rapidly, however, after dark-grown seedlings are transferred to light and the etioplasts develop into photosynthetically active chloroplasts. Light, therefore, triggers the degradation of DNA in maize chloroplasts. The cpDNA is retained in the leaf blade of seedlings grown under red, but not blue light. We suggest that light signaling pathways are involved in mediating cpDNA levels, and that red light promotes replication and inhibits degradation and blue light promotes degradation. For five of nine photosynthetic mutants, cpDNA levels in expanded leaves are higher than in wild type, indicating that nuclear genotype can affect the loss or retention of cpDNA.

Chloroplast DNA in Mature and Senescing Leaves: A Reappraisal

“…Our findings cannot be reconciled with those of Bendich and coworkers, who have claimed that ptDNA sharply declines or even vanishes completely from chloroplasts long before the onset of senescence in several species, notably including Arabidopsis and maize Rowan et al, 2004Rowan et al, , 2009Oldenburg et al, 2006;Shaver et al, 2006). The reasons for these differences are not entirely clear, but in our opinion, the reported findings are not conclusive because of artifact-prone methods and the lack of appropriate controls checking the biochemistry used.…”

“…In addition to the concerns previously raised by Li et al (2006), three examples may illustrate this. First, undetectability of stainable DNA, even if the plastids were not treated with DNase during the isolation procedure, is not a valid criterion per se to postulate the absence of DNA or to assess nature and impact of changes of in-gel DNA structures remaining after lysis of embedded chloroplasts Rowan et al, 2004Rowan et al, , 2009Oldenburg et al, 2006;Shaver et al, 2006). Besides possible technical problems with insufficient dye penetration (Selldé n and Leech, 1981;Evans et al, 2010), leaf tissue, especially if more mature, is known to contain endogenous nucleases that can be sufficiently active to destroy accessible DNA in organelle preparations (Selldé n and Leech, 1981).…”

“…It was concluded that, in fully expanded leaves, most chloroplasts contain no or only insignificant amounts of DNA long before the onset of leaf senescence Rowan et al, 2004;Oldenburg et al, 2006;Shaver et al, 2006;Rowan et al, 2009). Retention of ptDNA was proposed to be dispensable after the photosynthetic machinery was established in that the plastome-encoded photosynthesis genes were no longer needed in adult leaves.…”

“…However, since contradictory data were reported for the same species that were grown under comparable, if not identical, conditions (Rowan et al, 2004(Rowan et al, , 2009Li et al, 2006;Oldenburg et al, 2006;Shaver et al, 2006;Zoschke et al, 2007;Evans et al, 2010;Udy et al, 2012), it is apparent that some of them must reflect methodological insufficiencies of the experimental approaches employed.…”

Chloroplast DNA Replication Is Regulated by the Redox State Independently of Chloroplast Division in Chlamydomonas reinhardtii

“…Chloroplasts also contain multiple copies of DNA (approximately 1,000 copies; Boffey and Leech, 1982;Miyamura et al, 1986;Baumgartner et al, 1989;Oldenburg and Bendich, 2004;Oldenburg et al, 2006;Shaver et al, 2008). In algae, chloroplast DNA is replicated in a manner that keeps pace with chloroplast and cell division in order to maintain the proper DNA content per chloroplast (i.e.…”