Evidence for karyoplasmic homeostasis during endoreduplication and a ploidy-dependent increase in gene transcription during tomato fruit growth

Abstract

SUMMARYEndopolyploidy is a widespread process that corresponds to the amplification of the genome in the absence of mitosis. In tomato, very high ploidy levels (up to 256C) are reached during fruit development, concomitant with very large cell sizes. Using cellular approaches (fluorescence and electron microscopy) we provide a structural analysis of endoreduplicated nuclei at the level of chromatin and nucleolar organisation, nuclear shape and relationship with other cellular organelles such as mitochondria. We demonstrate that endopolyploidy in pericarp leads to the formation of polytene chromosomes and markedly affects nuclear structure. Nuclei manifest a complex shape, with numerous deep grooves that are filled with mitochondria, affording a fairly constant ratio between nuclear surface and nuclear volume. We provide the first direct evidence that endopolyploidy plays a role in increased transcription of rRNA and mRNA on a per-nucleus basis. Overall, our results provide quantitative evidence in favour of the karyoplasmic theory and show that endoreduplication is associated with complex cellular organisation during tomato fruit development.

Light signaling controls nuclear architecture reorganization during seedling establishment

“…To test this, overall RNA Pol II transcriptional activity was determined by quantifying the proportion of elongating (phosphorylated Serine 2, S2P) versus poised (nonphosphorylated, NP) RNA Pol II forms in individual cotyledon nuclei isolated from dark-and light-grown seedlings (51,52). Because ploidy levels significantly increase during cotyledon de-etiolation (29) and are positively correlated with the amount of RNA Pol II (53,54), measurements of S2P and NP RNA Pol II signals were obtained separately for the nuclei of each ploidy class (Fig. S6).…”

The Importance of Cardiolipin Synthase for Mitochondrial Ultrastructure, Respiratory Function, Plant Development, and Stress Responses in Arabidopsis

“…These two probes were used in parallel not only to explore complementary spectral domains but also to appreciate nonspecific binding (to lipids and waxes), which tends to be higher with DiOC 6 (5), even though it is a potential-sensitive dye, than with MitoTracker Red (Bourdon et al, 2012). Using confocal microscopy, we clearly identified active mitochondria in Col-0 leaf mesophyll ( Figure 4A) and epidermal ( Figure 4B) cells.…”

Tissue-Specific Control of the Endocycle by the Anaphase Promoting Complex/Cyclosome Inhibitors UVI4 and DEL1

“…Furthermore, endoreplication is believed to be an important trigger for cell and organ growth, because cell size is frequently correlated with the DNA ploidy levels (Melaragno et al, 1993;De Veylder et al, 2011), although such a relationship is not always observed (Beemster et al, 2002). In tomato (Solanum lycopersicum), increased ploidy levels are correlated with increased levels of rRNA and protein synthesis per-nucleus, indicating increased metabolism to support cell growth (Bourdon et al, 2012). Endoreplication has also been demonstrated to instruct cell fate, as observed for Arabidopsis trichomes .…”