Two E2F Elements Regulate the Proliferating Cell Nuclear Antigen Promoter Differently during Leaf Development

Abstract

E2F transcription factors regulate genes expressed at the G1/S boundary of the cell division cycle in higher eukaryotes. Although animal E2F proteins and their target promoters have been studied extensively, little is known about how these factors regulate plant promoters. An earlier study identified two E2F consensus binding sites in the promoter of a Nicotiana benthamiana gene encoding proliferating cell nuclear antigen (PCNA) and showed that the proximal element (E2F2) is required for the full repression of PCNA expression in mature leaves. In this study, we examined the distal element (E2F1) and how it interacts with the E2F2 site to regulate the PCNA promoter. Gel shift assays using plant nuclear extracts or purified Arabidopsis E2F and DP proteins showed that different complexes bind to the two E2F sites. Mutation of the E2F1 site or both sites differentially altered PCNA promoter function in transgenic plants. As reported previously for the E2F2 mutation, the E2F1 and E2F1+2 mutations partially relieved the repression of the PCNA promoter in mature leaves. In young tissues, the E2F1 mutation resulted in a threefold reduction in PCNA promoter activity, whereas the E2F1+2 mutation had no detectable effect. The activity of E2F1+2 mutants was indistinguishable from that of E2F2 mutants. These results demonstrate that both E2F elements contribute to the repression of the PCNA promoter in mature leaves, whereas the E2F1 site counters the repression activity of the E2F2 element in young leaves.

Regulation of theChlamydomonasCell Cycle by a Stable, Chromatin-Associated Retinoblastoma Tumor Suppressor Complex

“…This model for a stable ternary complex does not contradict the notion that the relative affinities of the subunits change during the cell cycle; indeed, such changes in affinity have been seen in vitro upon CDK phosphorylation of mammalian RB (Zheng et al, 1999;Burke et al, 2010), but altered affinity in vitro does not necessarily imply dissociation in vivo. Our model is consistent with the known association of RBrelated proteins with dozens of effectors, including chromatin modifying proteins, replication proteins, transcription factors, and others that may change in their temporal associations with RB-related proteins to regulate either cell cycle progression or differentiation (Williams and Grafi, 2000;Morris and Dyson, 2001;Egelkrout et al, 2002;Shen, 2002;Ausín et al, 2004;Mosquna et al, 2004;Magyar et al, 2005;Ramírez-Parra and Gutierrez, 2007;Burkhart and Sage, 2008;Jullien et al, 2008;van den Heuvel and Dyson, 2008;Chen et al, 2009;. Our findings provide a basis for further investigation of RB-E2F-DP complexes and how a stable ternary complex may be modified as a switch to drive cell cycle progression.…”

The Basic Helix-Loop-Helix Transcription Factor MYC2 Directly RepressesPLETHORAExpression during Jasmonate-Mediated Modulation of the Root Stem Cell Niche inArabidopsis

“…It is noteworthy that the effect of JA on CYCB1;1 pro :GUS expression was different from that of ethylene, which exerted little effect on CYCB1;1 pro : GUS expression (Rů zicka et al, 2007). Consistent with JAinduced reduction of CYCB1;1 pro :GUS expression, our quantitative RT-PCR (qRT-PCR) assays revealed that exogenous JA markedly reduces the expression levels of several cell cyclerelated genes, including CYCB1;1 (Fuerst et al, 1996), CDC2A (Martinez et al, 1992), KRP1 (Wang et al, 1997), and PCNA1 (Egelkrout et al, 2002) (Figure 2L). It is noteworthy that JA failed to repress the expression of cell cycle-related genes in coi1-2 and myc2-2 ( Figure 2L), indicating that JA negatively regulates cell division activity of the root meristem through COI1 and MYC2.…”

E2F RegulatesFASCIATA1, a Chromatin Assembly Gene Whose Loss Switches on the Endocycle and Activates Gene Expression by Changing the Epigenetic Status

“…The two E2F binding sites in the Nicotiana benthamiana PCNA gene contribute to the repression of the promoter in mature leaves. However, one E2F site counters the repression activity of the second E2F site in young leaves (Egelkrout et al, 2001(Egelkrout et al, , 2002. However, in the case of rice (Oryza sativa) PCNA, potential E2F binding sites mediate its transcriptional activation in dividing cells, but they do not participate in its repression in terminally differentiated cells (Kosugi and Ohashi, 2002).…”