Evidence for Plant-Conserved Region Mediated Trimeric CESAs in Plant Cellulose Synthase Complexes.

Higher plants synthesize cellulose using membrane-bound, six-lobed cellulose synthase complexes, each lobe containing trimeric cellulose synthases (CESAs). Although molecular biology reports support heteromeric trimers composed of different isoforms, a homomeric trimer was reported for in vitro studies of the catalytic domain of CESA1 of Arabidopsis (AtCESA1CatD) and confirmed in cryoEM structures of full-length CESA8 and CESA7 of poplar and cotton, respectively. In both structures, a small portion of the plant-conserved region (P-CR) forms the only contacts between catalytic domains of the monomers. We report inter-subunit lysine-crosslinks that localize to the small P-CR, negative-stain EM structure, and modeling data for homotrimers of AtCESA1CatD. Molecular dynamics simulations for AtCESA1CatD trimers based on the CESA8 cryoEM structure were stable and dependent upon a small set of residue contacts. The results suggest that homomeric CESA trimers may be important for the synthesis of primary and secondary cell walls and identify key residues for future mutagenic studies.

Positive and negative chemotaxis of enzyme-coated liposome motors.

The ability of cells or cell components to move in response to chemical signals is critical for the survival of living systems. This motion arises from harnessing free energy from enzymatic catalysis. Artificial model protocells derived from phospholipids and other amphiphiles have been made and their enzymatic-driven motion has been observed. However, control of directionality based on chemical cues (chemotaxis) has been difficult to achieve. Here we show both positive or negative chemotaxis of liposomal protocells. The protocells move autonomously by interacting with concentration gradients of either substrates or products in enzyme catalysis, or Hofmeister salts. We hypothesize that the propulsion mechanism is based on the interplay between enzyme-catalysis-induced positive chemotaxis and solute-phospholipid-based negative chemotaxis. Controlling the extent and direction of chemotaxis holds considerable potential for designing cell mimics and delivery vehicles that can reconfigure their motion in response to environmental conditions.

Rooting for cassava: insights into photosynthesis and associated physiology as a route to improve yield potential.

Contents 50 I. 50 II. 52 III. 54 IV. 55 V. 57 VI. 57 VII. 59 60 References 61 SUMMARY: As a consequence of an increase in world population, food demand is expected to grow by up to 110% in the next 30-35 yr. The population of sub-Saharan Africa is projected to increase by > 120%. In this region, cassava (Manihot esculenta) is the second most important source of calories and contributes c. 30% of the daily calorie requirements per person. Despite its importance, the average yield of cassava in Africa has not increased significantly since 1961. An evaluation of modern cultivars of cassava showed that the interception efficiency (ɛi ) of photosynthetically active radiation (PAR) and the efficiency of conversion of that intercepted PAR (ɛc ) are major opportunities for genetic improvement of the yield potential. This review examines what is known of the physiological processes underlying productivity in cassava and seeks to provide some strategies and directions toward yield improvement through genetic alterations to physiology to increase ɛi and ɛc . Possible physiological limitations, as well as environmental constraints, are discussed.

Ironing out the issues: integrated approaches to understanding iron homeostasis in plants.

Plants initialize responses to environmental changes at all levels, from signaling to translation and beyond. Such is the case for fluctuations in the availability of iron (Fe), one of the most critical micronutrients for plants. The results of these responses are physiological and morphological changes that lead to increased iron uptake from the rhizosphere, and recycling and reallocation of Fe, which must be properly localized within specific cells and cellular compartment for use. The use of reductionist approaches, in combination with in vivo and in situ Fe localization tools, has been able to shed light on critical signaling molecules, transcriptional regulators, transporters and other proteins involved in Fe homeostasis. Recent advances in elemental distribution and speciation analysis now enable detection and measurement of Fe and other elements at resolutions never seen before. Moreover, increasing use of systems biology approaches provide a substantially broader perspective of how Fe availability affects processes at many levels. This review highlights the latest in vivo and in situ iron localization approaches and some of the recent advances in understanding mechanisms that control Fe translocation. A broad perspective of how Fe localization data might one day be integrated with large-scale data to create models for Fe homeostasis is presented.