Endoreduplication of nuclear DNA in the developing maize endosperm

Abstract

Multiparametric flow cytometry was used to analyze the development of the endosperm in Zea mays L. during the period from 8 to 20 days after pollination (dap). Nuclear size, DNA content per nucleus, and frequencies of nuclei with varying properties were measured in preparations that included all of the endosperm nuclei of single kernels of the inbred strain A188. Characteristics of nuclear populations from different kernels on the same ear showed minimal variation. The dynamic changes of non-mitotic cells involved in endosperm development consisted of alternating periods of DNA replication with nonreplication. Seven rounds of DNA replication had occurred in some nuclei in the later developmental stages with the rate averaging approximately one round per 24-hour period. Analysis of the DNA levels in the nuclei showed an exact doubling pattern indicating an endoreduplication process, that is, replication of the entire genome during each round. The loosely organized polytenization of the chromatin occurred to varying extents among the nuclei within an endosperm. A weak positive correlation existed between DNA content and size of nuclei suggesting that DNA increases and nuclear growth may not be highly coordinated in this tissue. Increased proportions of the larger nuclei occurred in the later stages of endosperm development. Considering the entire endosperm, the average DNA content per nucleus at the 15-dap peak level was approximately 12.8 C constituting a 2.7-fold overall increase from 8 dap.

Plastid DNA in Developing Maize Endosperm

“…2 and 3) indicated that the maize endosperm plastid genome was indistinguishable from, and likely identical to, the maize chloroplast genome. The lack of distinguishable differences at the restriction site level is consistent with studies of nongreen plastids in pepper and tomato fruit, daffodil flowers, sycamore cell cultures, and wheat endosperm (2,7,11,15,22,24 (17, unpublished data); in addition, endosperm cell division is completed and the nuclear DNA copy number increases substantially (14).…”

“…A 2.4-kb transcript was the most abundant species in endosperm, whereas it was relatively low in leaf RNA. Although transcription of psaA was known to start on BamHI fragment 14 (5), no other genes had been previously mapped to this fragment of maize plastic DNA. Most of the psaA gene is on the adjacent BamHI fragment 17, which did not hybridize to the 2.4-kb transcript in endosperm RNA (Fig.…”

“…5). To help determine the origin of the abundant 2.4-kb transcript, we sequenced the BamHI fragment 14 (12). In maize, as in the corresponding regions of the Marchantia, tobacco, and rice plastid genomes (10, 23, 30), this region contains a highly conserved ORF (ORF170) composed of three exons (12).…”

Insights into the Effects of Long-Term Artificial Selection on Seed Size in Maize

“…Additionally, a number of cell-cycle-related genes were within the CNV regions. Cell-cycle programs are involved in multiple stages of endosperm development including acytokinetic mitosis, cellularization, cell proliferation, and in the cereals, endoreduplication (Kowles et al 1990;Sabelli and Larkins 2009). The presence of cell-cycle genes within CNV regions in this study provides additional support for a growing body of evidence demonstrating the role of master cell-cycle regulators in endosperm formation, development, and seed and plant size (Sabelli and Larkins 2009;Sekhon et al 2014).…”

Spatial relationship between chromosomal domains in diploid and autotetraploidArabidopsis thaliananuclei

“…It has been demonstrated that endoreduplicated nuclei are larger than their 2C counterparts. [18][19][20] Moreover, with concomitant rounds of endoreplication, the number and size of chromocentres also increase. 21,22 The former effect is probably caused by separation of centromeric domains of chromosomes, while their NORs remain associated.…”