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Integrating cell division and plant development
Abstracts / Comparative Biochemistry and Physiology, Part A 150 (2008) S139–S147
wall, PD were randomly distributed. As the primary wall extended, PD became ‘twinned’ at the cell periphery, aligned with new cellulose microfibrils. Additional secondary pores were inserted into these sites at right angles to these, giving rise to pit fields composed of several paired PD. Our data are consistent with a model in which peripheral primary PD function as templates to clone additional secondary PD, spatially fixing the position of future pit fields. Contrary to published models that depict secondary PD as fusion profiles of adjacent primary PD, we provide new evidence that secondary PD arise from fissions of peripheral primary PD. Our data are supported by a computational model, ‘Plasmodesmap’, which accurately simulates the formation of pit fields during radial cell–wall extension, producing PD motifs with striking resemblance to those on fractured wall faces. doi:10.1016/j.cbpa.2008.04.347
S141
Leaf epidermal cells contain a cortical ER network comprised of tubules, cisternae and three way junctions. Golgi bodies appear intimately associated with this network, which overlies the actin cytoskeleton. Upon depolymerisation of the actin the network remains intact indicating that additional factors are required for the coordinated response(s) required for the morphological changes from tubules to cisternae and vice versa. Recently, members of a class of proteins termed reticulons were shown in yeast and mammals to modulate ER morphology. Arabidopsis contains at least 19 genes encoding for reticulon-like proteins. We have characterised the shortest member of the family, RTNLB13 (Tolley et al., 2008 Traffic 9:94–102). Overexpression of fluorescent fusions indicate that RTNLB13 is located on the ER, and based on FRAP studies constricts the ER lumen. However, this severe phenotype does not appear to affect Golgi body movement, number, shape or secretion of a reporter protein. Future studies are required to understand the cellular requirement for tubules versus cisternal ER, and whether alterations in this ratio through manipulating reticulon expression levels could affect secretion at the macroscopic level.
C1/P4.9 SNAREs at the traffic junction with signalling, transport and nutrition
doi:10.1016/j.cbpa.2008.04.349
M. Blatt (University of Glasgow); I. Johansson (University of Glasgow); M. Paneque (University of Chile); R. Pratelli (Carnegie Institution of Washington); P. Campanoni (Philip Morris Intnl); S. Sokolovski (University of Dundee); A. Honsbein (University of Glasgow)
C1/P4.11 Integrating cell division and plant development J. Murray (University of Cambridge)
SNARE proteins contribute to vesicle targeting and membrane fusion in all eukaryotic cells, and are essential to the mechanics of cell growth and development. Nonetheless, there is clear evidence that SNAREs play additional roles, for example in facilitating cellular signalling and synaptic transmission. I report here that SYP121, an Arabidopsis SNARE found at the plasma membrane, contributes to scaffolds that anchor ion channels within the plane of the membrane, and it is a critical structural element determining the K+ channel gating and K+ mineral nutrition. Work from my laboratory has shown that SYP121 interacts in vitro and in vivo with the regulatory (‘silent’) K+ channel subunit KC1 which assembles with different inwardrectifying K+ channels to affect their activities in the plant.SYP121-KC1 interaction was found to be specific to these two protein partners and to be essential for the activity of K+ channels, channel-mediated K+ uptake at the root epidermis and for growth. Electrophysiological studies have shown changes in channel gating that can only result from an altered conformation of the channel and profound changes in the exposure of the channel voltage sensor to the membrane electric field. Intriguingly, when heterologously expressed on its own AKT1 does yield an inward-rectifying K+ current, but its gating characteristics – and those of AKT1 expressed together with KC1 – differ significantly from the K+ current in vivo unless co-expressed together with SYP121. In short, SYP121 is a missing component of the K+ channel complex and is essential for its gating in the plant. These results demonstrate a wholly unexpected role for a SNARE in eukaryotes as part of protein complex facilitating mineral nutrition and wholly unrelated to signalling or to membrane vesicle traffic.
Plant growth is characterised by a continuous indeterminate pattern of growth and the repeated initiation of organs. Growth is ultimately driven by the process of cell division coupled with the subsequent expansion and differentiation of the resulting cells. Both these processes depend on cell cycles-mitotic cycles during the phase of cell production and endocycles during the phase of cell expansion. During organ formation or root growth these two aspects are spatially and/or temporally distinct and the transition between them controls the cellular composition of organs. I will review the overall regulation of cell division in plant growth and development, and focus on data that show a key role for D-type (CYCD) cyclin activity in determining cell division rates and the transition from mitotic to endocycles in leaves and roots. doi:10.1016/j.cbpa.2008.04.350
C1/P4.12 Cyclin dependent protein kinase substrates: Insights into growth control by cell cycle regulators J. Doonan (John Innes Centre); O. Pierrat (John Innes Centre); M. Bush (John Innes Centre); K. Alexiou (John Innes Centre); V. Mikitova (John Innes Centre); G. Kitosis (Athens University); C. Pignocchi (John Innes Centre); L. Mayberry (University of Texas); K. Browning (University of Texas)
doi:10.1016/j.cbpa.2008.04.348
C1/P4.10 Role of reticulons on ER morphology and secretion I. Sparkes (Oxford Brookes University); N. Tolley (Warwick University); C. Hawes (Oxford Brookes University); L. Frigerio (Warwick University)
The plant Cyclin Dependent Protein Kinases (CDKs) comprise a family of at least 8 structurally related kinases, CDKA to G, with diverse cellular functions. Although CDKA is particularly well known for its roles in cell cycle progression, the targets of plant CDKs are not so well understood. As a first step towards understanding CDK function we have undertaken a search for CDK substrates. Bio-informatic analyses and yeast 2-H screens indicate that CDKA interacts with a wide variety of potential substrates and regulatory
wall, PD were randomly distributed. As the primary wall extended, PD became ‘twinned’ at the cell periphery, aligned with new cellulose microfibrils. Additional secondary pores were inserted into these sites at right angles to these, giving rise to pit fields composed of several paired PD. Our data are consistent with a model in which peripheral primary PD function as templates to clone additional secondary PD, spatially fixing the position of future pit fields. Contrary to published models that depict secondary PD as fusion profiles of adjacent primary PD, we provide new evidence that secondary PD arise from fissions of peripheral primary PD. Our data are supported by a computational model, ‘Plasmodesmap’, which accurately simulates the formation of pit fields during radial cell–wall extension, producing PD motifs with striking resemblance to those on fractured wall faces. doi:10.1016/j.cbpa.2008.04.347
S141
Leaf epidermal cells contain a cortical ER network comprised of tubules, cisternae and three way junctions. Golgi bodies appear intimately associated with this network, which overlies the actin cytoskeleton. Upon depolymerisation of the actin the network remains intact indicating that additional factors are required for the coordinated response(s) required for the morphological changes from tubules to cisternae and vice versa. Recently, members of a class of proteins termed reticulons were shown in yeast and mammals to modulate ER morphology. Arabidopsis contains at least 19 genes encoding for reticulon-like proteins. We have characterised the shortest member of the family, RTNLB13 (Tolley et al., 2008 Traffic 9:94–102). Overexpression of fluorescent fusions indicate that RTNLB13 is located on the ER, and based on FRAP studies constricts the ER lumen. However, this severe phenotype does not appear to affect Golgi body movement, number, shape or secretion of a reporter protein. Future studies are required to understand the cellular requirement for tubules versus cisternal ER, and whether alterations in this ratio through manipulating reticulon expression levels could affect secretion at the macroscopic level.
C1/P4.9 SNAREs at the traffic junction with signalling, transport and nutrition
doi:10.1016/j.cbpa.2008.04.349
M. Blatt (University of Glasgow); I. Johansson (University of Glasgow); M. Paneque (University of Chile); R. Pratelli (Carnegie Institution of Washington); P. Campanoni (Philip Morris Intnl); S. Sokolovski (University of Dundee); A. Honsbein (University of Glasgow)
C1/P4.11 Integrating cell division and plant development J. Murray (University of Cambridge)
SNARE proteins contribute to vesicle targeting and membrane fusion in all eukaryotic cells, and are essential to the mechanics of cell growth and development. Nonetheless, there is clear evidence that SNAREs play additional roles, for example in facilitating cellular signalling and synaptic transmission. I report here that SYP121, an Arabidopsis SNARE found at the plasma membrane, contributes to scaffolds that anchor ion channels within the plane of the membrane, and it is a critical structural element determining the K+ channel gating and K+ mineral nutrition. Work from my laboratory has shown that SYP121 interacts in vitro and in vivo with the regulatory (‘silent’) K+ channel subunit KC1 which assembles with different inwardrectifying K+ channels to affect their activities in the plant.SYP121-KC1 interaction was found to be specific to these two protein partners and to be essential for the activity of K+ channels, channel-mediated K+ uptake at the root epidermis and for growth. Electrophysiological studies have shown changes in channel gating that can only result from an altered conformation of the channel and profound changes in the exposure of the channel voltage sensor to the membrane electric field. Intriguingly, when heterologously expressed on its own AKT1 does yield an inward-rectifying K+ current, but its gating characteristics – and those of AKT1 expressed together with KC1 – differ significantly from the K+ current in vivo unless co-expressed together with SYP121. In short, SYP121 is a missing component of the K+ channel complex and is essential for its gating in the plant. These results demonstrate a wholly unexpected role for a SNARE in eukaryotes as part of protein complex facilitating mineral nutrition and wholly unrelated to signalling or to membrane vesicle traffic.
Plant growth is characterised by a continuous indeterminate pattern of growth and the repeated initiation of organs. Growth is ultimately driven by the process of cell division coupled with the subsequent expansion and differentiation of the resulting cells. Both these processes depend on cell cycles-mitotic cycles during the phase of cell production and endocycles during the phase of cell expansion. During organ formation or root growth these two aspects are spatially and/or temporally distinct and the transition between them controls the cellular composition of organs. I will review the overall regulation of cell division in plant growth and development, and focus on data that show a key role for D-type (CYCD) cyclin activity in determining cell division rates and the transition from mitotic to endocycles in leaves and roots. doi:10.1016/j.cbpa.2008.04.350
C1/P4.12 Cyclin dependent protein kinase substrates: Insights into growth control by cell cycle regulators J. Doonan (John Innes Centre); O. Pierrat (John Innes Centre); M. Bush (John Innes Centre); K. Alexiou (John Innes Centre); V. Mikitova (John Innes Centre); G. Kitosis (Athens University); C. Pignocchi (John Innes Centre); L. Mayberry (University of Texas); K. Browning (University of Texas)
doi:10.1016/j.cbpa.2008.04.348
C1/P4.10 Role of reticulons on ER morphology and secretion I. Sparkes (Oxford Brookes University); N. Tolley (Warwick University); C. Hawes (Oxford Brookes University); L. Frigerio (Warwick University)
The plant Cyclin Dependent Protein Kinases (CDKs) comprise a family of at least 8 structurally related kinases, CDKA to G, with diverse cellular functions. Although CDKA is particularly well known for its roles in cell cycle progression, the targets of plant CDKs are not so well understood. As a first step towards understanding CDK function we have undertaken a search for CDK substrates. Bio-informatic analyses and yeast 2-H screens indicate that CDKA interacts with a wide variety of potential substrates and regulatory