E2FB Interacts with RETINOBLASTOMA RELATED and Regulates Cell Proliferation during Leaf Development

Abstract

0000-0001-8376-7220 (Z.M.).Cell cycle entry and quiescence are regulated by the E2F transcription factors in association with RETINOBLASTOMA-RELATED (RBR). E2FB is considered to be a transcriptional activator of cell cycle genes, but its function during development remains poorly understood. Here, by studying E2FB-RBR interaction, E2F target gene expression, and epidermal cell number and shape in e2fb mutant and overexpression lines during leaf development in Arabidopsis (Arabidopsis thaliana), we show that E2FB in association with RBR plays a role in the inhibition of cell proliferation to establish quiescence. In young leaves, both RBR and E2FB are abundant and form a repressor complex that is reinforced by an autoregulatory loop. Increased E2FB levels, either by expression driven by its own promoter or ectopically together with DIMERIZATION PARTNER A, further elevate the amount of this repressor complex, leading to reduced leaf cell number. Cell overproliferation in e2fb mutants and in plants overexpressing a truncated form of E2FB lacking the RBR binding domain strongly suggested that RBR repression specifically acts through E2FB. The increased number of small cells below the guard cells and of fully developed stomata indicated that meristemoids preferentially hyperproliferate. As leaf development progresses and cells differentiate, the amount of RBR and E2FB gradually declined. At this stage, elevation of E2FB level can overcome RBR repression, leading to reactivation of cell division in pavement cells. In summary, E2FB in association with RBR is central to regulating cell proliferation during organ development to determine final leaf cell number. 518

E2FA and E2FB transcription factors coordinate cell proliferation with seed maturation

“…To analyse the spatial and temporal patterns of E2FA, E2FB and RBR proteins specifically in the developing embryos, we used our transgenic Arabidopsis lines expressing fluorescent protein-tagged E2FA, E2FB or RBR under the control of their own promoters (pgE2FA-3xvYFP, pgE2FB-3xvYFP, pgRBR-3xCFP; O˝szi et al, 2019). Immature embryos were dissected from transgenic Arabidopsis seeds at various developmental stages and fluorescence signals were analysed by confocal laser microscopy (Fig.…”

“…2. Spatial and temporal regulation of E2FA and E2FB accumulation during embryogenesis. (A-C) Representative confocal microscopy images of developing embryos dissected from immature seeds of pgE2FA-3xvYFP (A) and pgE2FB-3xvYFP (B) transgenic lines (O˝szi et al, 2019). White dashed boxes outline the epidermal regions of hypocotyls and cotyledon in the post-mature E2FA-3xvYFP (left side) and E2FB-3xvYFP (right side) embryos, magnified in (C).…”

“…Transgenic lines expressing the 3xvYFP-tagged E2FA (pgE2FA-3xvYFP) or E2FB (pgE2FB-3xvYFP) have been recently described (O˝szi et al, 2019). The genomic sequence of RBR was fused in frame with 3xCFP in a pGreenII-based pGII0125 destination vector by using the Invitrogen 3way Gateway System (Thermo Fisher Scientific).…”

In Silico Characterization of a Cyclin Dependent Kinase -A (CDKA) and its Coding Gene in some Oryza Species

“…Except for O. longistaminata with molecular weight of 31.29 KDa and isoelecteric point of 6.22 (Table 1), physiochemical characteristics of the mined CDKAs in other taxa showed narrow ranges of molecular weights (33.56 -33.69 KDa) and isoelecteric points (6.38 -6.97). CDKAs having similar characteristics were identified in Physcomitrella patens (31), Dendrobium candidum (46), maize endosperm (48) and Arabidopsis thaliana (49).…”

Beyond What Your Retina Can See: Similarities of Retinoblastoma Function between Plants and Animals, from Developmental Processes to Epigenetic Regulation

“…In contrast, nine E2F are found in humans (three activators and six repressors), and only six in Arabidopsis. Of these, AtE2Fa functions as activator, AtE2Fb functions either as an activator or repressor, depending on the plant developmental stages; E2Fc is a repressor; and the other three members of this family (E2Fd/e/f) are atypical since they have a duplicated DNA-binding domain, do not heterodimerize with DP and lack the trans-activating and Rb pocket-binding domains, and thus resemble E2F7/8 in animals [ 130 , 131 , 132 , 133 ]. Finally, some components of the cell cycle regulatory machinery are plant-specific such as type B cyclin dependent kinases (CDKB1/2) [ 134 , 135 ], while others are animal-specific, such as cyclin E in humans [ 136 , 137 ].…”