Endoreduplication as a part of flower ontogeny in Trifolium pratense cultivars

The trxG protein ULT1 regulates Arabidopsis organ size by interacting with TCP14/15 to antagonize the LIM peptidase DA1 for H3K4me3 on target genes

Plant organ size is an important agronomic trait that makes a significant contribution to plant yield. Despite its central importance, the genetic and molecular mechanisms underlying organ size control remain to be fully clarified. Here, we report that the trithorax group protein ULTRAPETALA1 (ULT1) interacts with the TEOSINTE BRANCHED1/CYCLOIDEA/PCF14/15 (TCP14/15) transcription factors by antagonizing the LIN-11, ISL-1, and MEC-3 (LIM) peptidase DA1, thereby regulating organ size in Arabidopsis. Loss of ULT1 function significantly increases rosette leaf, petal, silique, and seed size, whereas overexpression of ULT1 results in reduced organ size. ULT1 associates with TCP14 and TCP15 to co-regulate cell size by affecting cellular endoreduplication. Transcriptome analysis revealed that ULT1 and TCP14/15 regulate common target genes involved in endoreduplication and leaf development. ULT1 can be recruited by TCP14/15 to promote lysine 4 of histone H3 trimethylation at target genes, activating their expression to determine final cell size. Furthermore, we found that ULT1 influences the interaction of DA1 and TCP14/15 and antagonizes the effect of DA1 on TCP14/15 degradation. Collectively, our findings reveal a novel epigenetic mechanism underlying the regulation of organ size in Arabidopsis.

Endoreduplication in plant organogenesis: a means to boost fruit growth

Endoreduplication is the major source of somatic endopolyploidy in higher plants, and leads to variation in cell ploidy levels due to iterative rounds of DNA synthesis in the absence of mitosis. Despite its ubiquitous occurrence in many plant organs, tissues, and cells, the physiological meaning of endoreduplication is not fully understood, although several roles during plant development have been proposed, mostly related to cell growth, differentiation, and specialization via transcriptional and metabolic reprogramming. Here, we review recent advances in our knowledge of the molecular mechanisms and cellular characteristics of endoreduplicated cells, and provide an overview of the multi-scale effects of endoreduplication on supporting growth in plant development. In addition, the effects of endoreduplication in fruit development are discussed, since it is highly prominent during fruit organogenesis where it acts as a morphogenetic factor supporting rapid fruit growth, as illustrated by case of the model fleshy fruit, tomato (Solanum lycopersicum).

Evolutionary and functional potential of ploidy increase within individual plants: somatic ploidy mapping of the complex labellum of sexually deceptive bee orchids

Background and Aims

Recent tissue-level observations made indirectly via flow cytometry suggest that endoreplication (duplication of the nuclear genome within the nuclear envelope in the absence of subsequent cell division) is widespread within the plant kingdom. Here, we also directly observe ploidy variation among cells within individual petals, relating size of nucleus to cell micromorphology and (more speculatively) to function.

Methods

We compared the labella (specialized pollinator-attracting petals) of two European orchid genera: Dactylorhiza has a known predisposition to organismal polyploidy, whereas Ophrys exhibits exceptionally complex epidermal patterning that aids pseudocopulatory pollination. Confocal microscopy using multiple staining techniques allowed us to observe directly both the sizes and the internal structures of individual nuclei across each labellum, while flow cytometry was used to test for progressively partial endoreplication.

Key Results

In Dactylorhiza, endoreplication was comparatively infrequent, reached only low levels, and appeared randomly located across the labellum, whereas in Ophrys endoreplication was commonplace, being most frequent in large peripheral trichomes. Endoreplicated nuclei reflected both endomitosis and endocycling, the latter reaching the third round of genome doubling (16C) to generate polytene nuclei. All Ophrys individuals studied exhibited progressively partial endoreplication.

Conclusions

Comparison of the two genera failed to demonstrate the hypothesized pattern of frequent polyploid speciation in genera showing extensive endoreplication. Endoreplication in Ophrys appears more strongly positively correlated with cell size/complexity than with cell location or secretory role. Epigenetic control of gene overexpression by localized induction of endoreplication within individual plant organs may represent a significant component of a plant's developmental programme, contributing substantially to organ plasticity.