If you cannot move, send messengers: how cells organize space

Protoplasma, Mar 2016

Peter Nick

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If you cannot move, send messengers: how cells organize space

Protoplasma If you cannot move, send messengers: how cells organize space Peter Nick 0 0 Molecular Cell Biology, Karlsruhe Institute of Technology , Karlsruhe , Germany - Life is cellular—the description of cork Bcells^ by Robert Hooke 350 years ago turned out to be a general principle. Cells allow to delineate an internal space that is defended against fluctuations of the external world. The resilience of this internal homeostasis will decide, which environments can be conquered. However, adaptation of the interior is not the only strategy employed—multicellular organisms have achieved the ability to organize the space surrounding individual cells in a manner that adverse fluctuations can be buffered. There are two principle approaches to achieve this: Either cells differentiate (meaning that they establish, in a more or less stable manner, a different type of homeostasis) and move into different locations. Alternatively, cells that are not able to move (for instance plant cells) have to send out messengers that do this job. These messengers are usually of chemical nature—either macromolecules such as proteins or RNA species, or specific (i.e., secondary) metabolites. Three contributions in the current issue highlight different aspects of the second approach and show the activity of quite diverse mechanisms of transport, stimulating the general question, how these mechanisms are controlled in space and time. The review by Becker and Ehlers (2016) in the current issue considers the differentiation of leaf whorls into flower organs. The identity of sepals, petals, anthers, and carpels is controlled by dimeric complexes of transcription factors that steer the differentiation of the developing leaf primordium. The study of homeotic mutants of flower patterning, such as those already described by Johann Wolfgang v. Goethe more than two centuries ago, culminated in the ingenious ABC model, proposing that flower organ identity is defined by homo- or heterodimeric interaction of a limited number of genetic switches. What at first sight looked like a fairly cell autonomous process, later turned out to be strongly controlled by transport of signals: Secretion of peptides and proteins controls the balance between stem cell maintenance and differentiation in the apical meristem. Far-distance signals are generated in the leaves in a complex response to day length and are then translocated as florigen to the apical meristem. And, floral identity is not cell autonomous either, but controlled by intensive exchange of transcriptional regulators. Flowering thus emerges as a process, where numerous cells from quite different locations in the plant communicate by macromolecular signals and channel cell fate in a very specific region of the apical meristem in a manner that will ensure efficient gene flow for the entire organism. This shifts abundance, location, and gating of plasmodesmata into the center of pattern formation (Burch-Smith et al. 2011) . A very specific and fundamental aspect of intracellular messengers is the interaction between the eukaryotic nucleus and the semi-autonomous organelles such as mitochondria and plastids that represent formerly independent prokaryotic organisms which had been Bdomesticated.^ Although some of the gene products required for the specific functions of these organelles are still encoded in the organelle genome, most genes had been transferred to the nucleus during the long history of domestication. This means that most proteins have to be imported and that this import has to be regulated depending on the demand in the organelle. The review by Paić and Fulgosi (2016) in the current issue highlights the role of specific immunophilins for maintenance and repair of plastid functionality. This group of proteins is as widespread as it has remained enigmatic. Although found in all life forms, their extreme functional versatility has left them somehow terminal cells. To address, whether possibly additional cells participate in the synthesis of these metabolites, authors use the approach to immunolabel one of the key enzyme, germacrane oxidase, and then to detect the signal either by fluorescence microscopy or, after immunogold labelling, by transmission electron microscopy. The authors can show that the enzyme is linked with the smooth ER, and they find, unexpectedly, that it is not only present in the terminal cell, but also in the subapical cells of the stalk. This leads to the question, how the product is translocated to the subcuticular compartment, which is located in quite some distance. Since plasmodesmata between the cells of the gland are scarce, they arrive at the conclusion that transport is likely to be apoplastic. Compliance with ethical standards Conflict of interest The author declares that there is no conflict of interest. Amrehn E , Aschenbrenner AK , Heller AR , Spring O ( 2016 ) Localization of sesquiterpene lactone biosynthesis in cells of capitate glandular trichomes of Helianthus annuus (Asteraceae) Amrehn E , Heller A , Spring O ( 2014 ) Capitate glandular trichomes of Helianthus annuus (Asteraceae): ultrastructure and cytological development . Protoplasma 251 : 161 - 167 Becker A , Ehlers K ( 2016 ) Arabidopsis flower development-of protein complexes, targets, and transport . Protoplasma, current issue Burch-Smith TM , Stonebloom S , Xu M , Zambryski PC ( 2011 ) Plasmodesmata during development: re-examination of the importance of primary, secondary, and branched plasmodesmata structure versus function . Protoplasma 248 : 61 - 74 Paić A , Fulgosi H ( 2016 ) Chloroplast immunophilins . Protoplasma, current issue Talbot ME , Offler CE , McCurdy DW ( 2002 ) Transfer cell wall architecture: a contribution towards understanding localized wall deposition . Protoplasma 219 : 197 - 209

This is a preview of a remote PDF: http://link.springer.com/content/pdf/10.1007%2Fs00709-016-0949-z.pdf

Peter Nick. If you cannot move, send messengers: how cells organize space, Protoplasma, 2016, 217-218, DOI: 10.1007/s00709-016-0949-z