Phytochrome controls the number of endoreduplication cycles in the Arabidopsis thaliana hypocotyl

Abstract

SummaryA majority of the cells in the Arabidopsis hypocotyl undergo endoreduplication. The number of endocycles in this organ is partially controlled by light. Up to two cycles occur in light-grown hypocotyls, whereas in the dark about 30% of the cells go through a third cycle. Is the inhibition of the third endocycle in the light an indirect result of the reduced cell size in the light-grown hypocotyl, or is it under independent light control? To address this question, the authors examined the temporal and spacial patterns of endoreduplication in light-or dark-grown plants and report here on the following observations: (i) during germination two endocycles take place prior to any significant cell expansion; (ii) in the dark the third cycle is completed very early during cell growth; and (iii) a mutation that dramatically reduces cell size does not interfere with the third endocycle. The authors then used mutants to study the way light controls the third endocycle and found that the third endocycle is completely suppressed in far red light through the action of phytochrome A and, to a lesser extent, in red light by phytochrome B. Furthermore, no 16C nuclei were observed in dark-grown constitutive photomorphogenic 1 seedlings. And, finally the hypocotyl of the cryptochrome mutant, hy4, grown in blue light was about three times longer than that of the wild-type without a significant difference in ploidy levels. Together, the results support the view that the inhibition of the third endocycle in light-grown hypocotyls is not the consequence of a simple feed-back mechanism coupling the number of cycles to the cell volume, but an integral part of the phytochrome-controlled photomorphogenic program.

In planta quantification of endoreduplication using fluorescent in situ hybridization (FISH)

“…Our initial attempts to analyze the in situ polyploidization pattern in tomato pericarp relied on DAPI fluorescence intensity measurement on digital images, using a method similar to that of Gendreau et al (1998). However, we were rapidly confronted with difficulties related to the structural characteristics of tomato pericarp.…”

“…Endopolyploidy has been described as being associated with increased gene expression (Galitski et al, 1999;Raslova et al, 2003) and increased cell growth (Lee et al, 2009). In plants, a strong correlation between cell size and endoreduplication has been reported in a broad range of species (Melaragno et al, 1993;Gendreau et al, 1998;Cheniclet et al, 2005;Jovtchev et al, 2006;Bourdon et al, 2010).…”

“…The in situ measurement of ploidy levels was achieved in Arabidopsis leaf and stem epidermis using a microspectrofluorometer (Melaragno et al, 1993). The fluorometric method was also used in combination with image analysis to directly measure the relative nuclear DNA content of individual cells from DAPI-stained Arabidopsis hypocotyls in situ (Gendreau et al, 1998) or in Arabidopsis meristematic cells treated with different drugs (Grandjean et al, 2004). So far the in situ measurement of ploidy levels by densitometric or fluorometric methods has been applied either to young tissues with small cells and nuclei, monolayer tissues (epidermis) or paraffin sections.…”

RHL1 is an essential component of the plant DNA topoisomerase VI complex and is required for ploidy-dependent cell growth

“…2), RHL1 is likely to have an essential role in ploidy-dependent cell growth in Arabidopsis. Endoreduplication is generally thought to provide a mechanism to increase cell size (3), although the corre- lation between ploidy level and cell size is not always tight (4,34,35). In rhl1-2 leaf epidermis, the maximum DNA content (Fig.…”

Eternal Youth, the Fate of Developing Arabidopsis Leaves uponRhodococcus fasciansInfection

“…During organ formation, primordium growth is initially driven by cell proliferation, whereas the second growth phase is primarily attributed to postmitotic cell expansion of the differentiating cells through endoreduplication and vacuolization (Donnelly et al, 1999;den Boer and Murray, 2000;Nath et al, 2003). Usually, ploidy levels and cell size are positively correlated, indicating that cell expansion and differentiation depend on the endocycle (Cionini et al, 1983;Melaragno et al, 1993;Gendreau et al, 1998;Joubès et al, 1999;Beemster et al, 2003;Tsukaya, 2006), but ploidy-independent growth mechanisms also exist (De Veylder et al, 2001;Beemster et al, 2002;Jasinski et al, 2002;Schnittger et al, 2003;Ferjani et al, 2007).…”