Expression, regulation and activity of a B2-type cyclin in mitotic and endoreduplicating maize endosperm

Abstract

Cyclin-dependent kinases, the master regulators of the eukaryotic cell cycle, are complexes comprised of a catalytic serine/threonine protein kinase and an essential regulatory cyclin. The maize genome encodes over 50 cyclins grouped in different types, but they have been little investigated. We characterized a type B2 cyclin (CYCB2;2) during maize endosperm development, which comprises a cell proliferation phase based on the standard mitotic cell cycle, followed by an endoreduplication phase in which DNA replication is reiterated in the absence of mitosis or cytokinesis. CYCB2;2 RNA was present throughout the period of endosperm development studied, but its level declined as the endosperm transitioned from a mitotic to an endoreduplication cell cycle. However, the level of CYCB2;2 protein remained relatively constant during both stages of endosperm development. CYCB2;2 was recalcitrant to degradation by the 26S proteasome in endoreduplicating endosperm extracts, which could explain its sustained accumulation during endosperm development. In addition, although CYCB2;2 was generally localized to the nucleus of endosperm cells, a lower molecular weight form of the protein accumulated specifically in the cytosol of endoreduplicating endosperm cells. In dividing cells, CYCB2;2 appeared to be localized to the phragmoplast and may be involved in cytokinesis and cell wall formation. Kinase activity was associated with CYCB2;2 in mitotic endosperm, but was absent or greatly reduced in immature ear and endoreduplicating endosperm. CYCB2;2-associated kinase phosphorylated maize E2F1 and the “pocket” domains of RBR1 and RBR3. CYCB2;2 interacted with both maize CDKA;1 and CDKA;3 in insect cells. These results suggest CYCB2;2 functions primarily during the mitotic cell cycle, and they are discussed in the context of the roles of cyclins, CDKs and proteasome activity in the regulation of the cell cycle during endosperm development.

Transcriptomic and metabolomics responses to elevated cell wall invertase activity during tomato fruit set

“…Overexpression of cycb2;2 in rice promoted root growth by increasing cell number ( Lee et al , 2003 ). Cycb2;2 has been recently reported to function in establishing rice grain size and yield ( Ishimaru et al , 2013 ) and cell wall formation in mitotic cells of maize endosperm ( Sabelli et al , 2014 ). Thus, up-regulated expression of two cyclinB genes in tomato ovaries by elevated CWIN activity may stimulate the cell cycle during fruit set.…”

Reciprocally Retained Genes in the Angiosperm Lineage Show the Hallmarks of Dosage Balance Sensitivity

“…Similarly, overexpression of Os-CYCB2;2 in rice promotes cell division and results in accelerated root growth (Lee et al, 2003). In contrast to most other B-type cyclins, maize (Zea mays) Zm-CYCB2;2 and Zm-CYCB2;1 persist until telophase and associate with the phragmoplast, and they are thought to be involved in cytokinesis and cell wall formation (Sabelli et al, 2014). It is conceivable that the dosage balance of B2-type cyclins and their CDK interactors is important for accurate regulation of the G2/M transition.…”

Cell Type-Specific Gene Expression Analyses by RNA Sequencing Reveal Local High Nitrate-Triggered Lateral Root Initiation in Shoot-Borne Roots of Maize by Modulating Auxin-Related Cell Cycle Regulation

“…Moreover, B1-and B2-type CDK proteins display a maximum of kinase activity at the G2-to-M transition and during mitosis (Inzé and De Veylder, 2006). In addition, CYCB2;2 promotes mitotic cell cycle and cell divisions probably through association with CDKB2 in the root meristem (Lee et al, 2003;Sabelli et al, 2014). In this study, qRT-PCR-based time-course experiments on stele-specific gene expression have been implemented to survey the effects of local high nitrate stimulation on the cell cycle.…”