MpTCP1 controls cell proliferation and redox processes in Marchantia polymorpha

TCP transcription factors are key regulators of angiosperm cell proliferation processes. It is unknown whether their regulatory growth capacities are conserved across land plants, which we examined in liverworts, one of the earliest diverging land plant lineages. We generated knockout mutants for MpTCP1, the single TCP‐P clade gene in Marchantia polymorpha, and characterized its function conducting cell proliferation and morphological analyses as well as mRNA expression, transcriptome, chemical and DNA binding studies. Mptcp1ge lines show a reduced vegetative thallus growth and extra tissue formation in female reproductive structures. Additionally, mutant plants reveal increased H2O2 levels and an enhanced pigmentation in the thallus caused by formation of secondary metabolites, such as aminochromes. MpTCP1 proteins interact redox‐dependently with DNA and regulate the expression of a comprehensive redox network, comprising enzymes involved in H2O2 metabolism. MpTCP1 regulates Marchantia growth context‐dependently. Redox sensitivity of the DNA binding capacity of MpTCP1 proteins provides a mechanism to respond to altered redox conditions. Our data suggest that MpTCP1 activity could thereby have contributed to diversification of land plant morphologies and to adaptations to abiotic and biotic challenges, experienced by liverworts during early land plant colonization

Arabidopsis KCBP interacts with AIR9 but stays in the cortical division zone throughout mitosis via its MyTH4-FERM domain

The preprophase band of microtubules performs the crucial function of marking the plane of cell division. Although the preprophase band depolymerises at the onset of mitosis, the division plane is 'memorized' by a cortical division zone to which the phragmoplast is attracted during cytokinesis. Proteins have been discovered that are part of the molecular memory but little is known about how they contribute to phragmoplast guidance. Previously, we found that the microtubule-associated protein AIR9 is found in the cortical division zone at preprophase and returns during cell plate insertion but is absent from the cortex during the intervening mitosis. To identify new components of the preprophase memory, we searched for proteins that interact with AIR9. We detected the kinesin-like calmodulin-binding protein, KCBP, which can be visualized at the predicted cortical site throughout division. A truncation study of KCBP indicates that its MyTH4-FERM domain is required for linking the motor domain to the cortex. These results suggest a mechanism by which minus-end-directed KCBP helps guide the centrifugally expanding phragmoplast to the cortical division site.Instituto de Biotecnologia y Biologia Molecula

Arabidopsis KCBP interacts with AIR9 but stays in the cortical division zone throughout mitosis via its MyTH4-FERM domain

The preprophase band of microtubules performs the crucial function of marking the plane of cell division. Although the preprophase band depolymerises at the onset of mitosis, the division plane is 'memorized' by a cortical division zone to which the phragmoplast is attracted during cytokinesis. Proteins have been discovered that are part of the molecular memory but little is known about how they contribute to phragmoplast guidance. Previously, we found that the microtubule-associated protein AIR9 is found in the cortical division zone at preprophase and returns during cell plate insertion but is absent from the cortex during the intervening mitosis. To identify new components of the preprophase memory, we searched for proteins that interact with AIR9. We detected the kinesin-like calmodulin-binding protein, KCBP, which can be visualized at the predicted cortical site throughout division. A truncation study of KCBP indicates that its MyTH4-FERM domain is required for linking the motor domain to the cortex. These results suggest a mechanism by which minus-end-directed KCBP helps guide the centrifugally expanding phragmoplast to the cortical division site.Instituto de Biotecnologia y Biologia Molecula

Origin and Diversification of Land Plant CC-Type Glutaredoxins

Glutaredoxins (GRXs) are ubiquitous glutathione-dependent oxidoreductase enzymes implicated in redox homeostasis, particularly oxidative stress response. Three major classes of GRX genes exist, the CPYC, CGFS classes are present in all pro- and eukaryote species, whereas the CC-type class GRXs are specific to land plants. In the basal land plant Physcomitrella patens, only two CC-type GRXs are present, compared with 21 in Arabidopsis. In contrast, sizes of the CPYC and CGFS classes remained rather similar throughout plant evolution, raising the interesting question as to when the CC-type GRXs first originated and how and why they expanded during land plant evolution. Recent evidence suggests that CC-type GRXs may have been recruited during evolution into diverse plant-specific functions of flower development (ROXY1, ROXY2) and pathogenesis response (ROXY19/GRX480). In the present study, GRX genes from the genomes of a range of green algae and evolutionarily diverse land plant species were identified; Ostreococcus, Micromonas, Volvox, Selaginella, Vitis, Sorghum, and Brachypodium. Previously identified sequences from Chlamydomonas, Physcomitrella, Oryza, Arabidopsis, and Populus were integrated to generate a more comprehensive understanding of the forces behind the evolution of various GRX classes. The analysis indicates that the CC-type GRXs probably arose by diversification from the CPYC class, at a time coinciding with colonization of land by plants. This strong differential expansion of the CC-type class occurred exclusively in the angiosperms, mainly through paleopolyploidy duplication events shortly after the monocot–eudicot split, and more recently through multiple tandem duplications that occurred independently in five investigated angiosperm lineages. The presented data suggest that following duplications, subfunctionalization, and subsequent neofunctionalization likely facilitated the sequestration of land plant-specific CC-type GRXs into novel functions such as development and pathogenesis response

Continuous-time modeling of cell fate determination in Arabidopsis flowers

<p>Abstract</p> <p>Background</p> <p>The genetic control of floral organ specification is currently being investigated by various approaches, both experimentally and through modeling. Models and simulations have mostly involved boolean or related methods, and so far a quantitative, continuous-time approach has not been explored.</p> <p>Results</p> <p>We propose an ordinary differential equation (ODE) model that describes the gene expression dynamics of a gene regulatory network that controls floral organ formation in the model plant <it>Arabidopsis thaliana</it>. In this model, the dimerization of MADS-box transcription factors is incorporated explicitly. The unknown parameters are estimated from (known) experimental expression data. The model is validated by simulation studies of known mutant plants.</p> <p>Conclusions</p> <p>The proposed model gives realistic predictions with respect to independent mutation data. A simulation study is carried out to predict the effects of a new type of mutation that has so far not been made in <it>Arabidopsis</it>, but that could be used as a severe test of the validity of the model. According to our predictions, the role of dimers is surprisingly important. Moreover, the functional loss of any dimer leads to one or more phenotypic alterations.</p