The Beauty of the Small

PUBLISHED: 3 MARCH 2017 | VOLUME: 3 | ARTICLE NUMBER: 17035 editorial The beauty of the small

Plant biology has a long history in helping to illuminate the most detailed workings of living organisms. This tradition is amply represented by a trio of structures appearing this month.

In this issue of Nature Plants, there are three proteins. Only around 4% of the yearly entries provide one of the greatest challenges in Articles reporting the atomic structures of into the Protein Data Bank (http://www.rcsb. structural biology: the photosystems at the plant proteins1–3. This slightly surprised us; org/pdb/) have a plant origin. heart of photosynthesis. Not only are the enough that we have joked about temporarily Nevertheless, there are many interesting photosystems integral to the chloroplast changing the journal’s name to reflect this structures and unique research questions to thylakoid membrane, which immediately unusual concentration of structural papers. be answered. For example, Hirano et al.1 have causes problems for conventional It should not have done. The nanoscale investigated the interactions that lie at the crystallography. They are also composed workings of the machinery of plants are heart of root patterning by determining the of multiple protein subunits and around no less important than those of any other structure of a heterodimer of SCARECROW a hundred or more cofactors, all of which division of life. In fact, ‘plant structural (SCR) and SHORT-ROOT (SHR), both on are needed to understand photosystem biology’ has been at the heart of a number of its own and when bound to the transcription functioning. Worse yet, they have a dynamic fundamental advances in biology. factor JACKDAW (JKD). These specific relationship with additional components, Consider cell theory. In the seventeenth interactions are important for determining including the hardly less complicated light- century, Robert Hooke was using the cutting- cell fates in the developing root, but SCR harvesting complexes, forming and reforming edge technology of the time, the microscope, and SHR are also representatives of a large supercomplexes dependent on exact to look at the natural world. He described his family of transcriptional regulators known conditions in the chloroplast. observations in his 1665 book Micrographia, as GRAS proteins due to their homologous As long ago as 1988, Johann Deisenhofer, which arose from a commission by Charles II GRAS domains. There are 33 such proteins Robert Huber and Hartmut Michel were of England (by way of Christopher Wren) encoded in the Arabidopsis genome and twice awarded the Nobel prize for chemistry to perform microscopic studies of insects. that number in rice, providing the potential for their determination of the structure of Hooke took upon himself a wider remit, for a diversity of functions through their the photosynthetic reaction centre from a looking at other materials, including thin ability to promiscuously dimerize. That any bacterium, equivalent to a small part of an slices of cork. In these he saw empty spaces of the possible partnerships can associate entire plant reaction centre. In this issue, surrounded by solid walls, which he named with various members of the BIRD family we are publishing a further step towards ‘cells’. Not content with just observing, of transcription factors, of which JKD is the full structural understanding of the Hooke used his 50× magnifying microscope a representative, leads to a highly flexible plant photosystems, with a 2.6 Å resolution to calculate that there would be almost system of developmental control unique structure of photosystem 1 (PSI) from pea3. 1,260 million cells in a cubic inch. to plants. This is not the first PSI structure. By the early twentieth century, the Wang et al.2 also look at a plant-specific This group, under the leadership of first studies of biological molecules using process: chloroplast division. Chloroplasts Nathan Nelson, published a 4.4 Å structure in X-ray diffraction were being undertaken, and other plastids are double-membrane 2003 (ref. 4), and this most recent structure including ones on cotton. In the 1920s, two intracellular organelles that must divide improves on 2.8 Å structures that were German chemists, Kurt Heinrich Meyer autonomously in order to maintain their published in 2015 (refs 5,6). While this may and Herman Francis Mark, obtained numbers in daughter cells during cell sound like a small difference, the extra 0.2 Å diffraction patterns from cotton and used division. This is achieved by the action of brings with it visualisation of additional these to support the theory that such fibres two contractile rings, one on the interior of protein, water and lipid components, all consisted of long macromolecules of regularly the inner envelope membrane, formed by contributing to a better understanding of the repeating, covalently bonded subunits. For the protein FtsZ, and one on the cytosolic functioning of this light-driven machine. cotton, or rather the cellulose that is its side of the outer envelope, assembled from Structural biology has never been more major component, the subunit consisted ARC5. For successful chloroplast division, important to our understanding of the of two glucose molecules. It is difficult to the activities of these two rings must be mechanics of life with constant technical overestimate the influence of Meyer and co-ordinated. This is achieved by the proteins advances bringing with them ever finer acuity. Mark and their work on the development PDV2 and ARC6, which span the outer and Nature Plants will strive to present the very of structural biology. Their X-ray pictures inner envelope membranes, respectively, best of these structural studies with particular inspired William Astbury in Leeds, UK, to and reach across the intermembrane space relevance to plants; although we won’t be conclude that his diffraction patterns from to bind with each other. This interaction changing the journal’s name any time soon! ❐ keratin demonstrated that fibrous proteins must be relatively weak to establish dynamic were also polymers, but of amino acids communication between the two proteins, References rather than sugars. Mark also taught X-ray making the task of imaging their complex 1. Hirano, Y. et al. Nat. Plants 3, 17010 (2017). diffraction to Linus Pauling and Max Perutz, doubly difficult. Wang et al. solved this 2. Wang, W. et al. Nat. Plants 3, 17011 (2017). 3. Mazor, Y., Borovikova, A., Caspy, I. & Nelson, N. Nat. Plants both of who subsequently won Nobel prizes particular problem by linking the interacting 3, 17014 (2017). for different aspects of structural biology. domains of PDV2 and ARC6 together with a 4. Ben-Shem, A., Frolow, F. & Nelson, N. Nature Despite this early importance of plant flexible tether. 426, 630–635 (2003). 5. Mazor, Y., Borovikova, A. & Nelson, N. eLife 4, e07433 (2015). structures, the focus of early molecular and Such technical difficulties occur with 6. Qin, X., Suga, M., Kuang, T. & Shen, J. R. Science structural biology was much more on animal systems from all branches of life, but plants 348, 989–995 (2015).