Crystal structure of a conserved domain in the intermembrane space region of the plastid division protein ARC6

The chloroplast division machinery is composed of numerous proteins that assemble as a large complex to divide double‐membraned chloroplasts through binary fission. A key mediator of division‐complex formation is ARC6, a chloroplast inner envelope protein and evolutionary descendant of the cyanobacterial cell division protein Ftn2. ARC6 connects stromal and cytosolic contractile rings across the two membranes through interaction with an outer envelope protein within the intermembrane space (IMS). The ARC6 IMS region bears a structurally uncharacterized domain of unknown function, DUF4101, that is highly conserved among ARC6 and Ftn2 proteins. Here we report the crystal structure of this domain from Arabidopsis thaliana ARC6. The domain forms an α/β barrel open towards the outer envelope membrane but closed towards the inner envelope membrane. These findings provide new clues into how ARC6 and its homologs contribute to chloroplast and cyanobacterial cell division.     

YSL3-mediated copper distribution is required for fertility,seed size and protein accumulation in Brachypodium

Addressing the looming global food security crisis requires the development of high-yielding crops. In agricultural soils, deficiency in the micronutrient copper significantly decreases grain yield in wheat (Triticum aestivum), a globally important crop. In cereals, grain yield is determined by inflorescence architecture, flower fertility, grain size, and weight. Whether copper is involved in these processes, and how it is delivered to the reproductive organs is not well understood. We show that copper deficiency alters not only the grain set but also flower development in both wheat and its recognized model, Brachypodium distachyon. We then show that the Brachypodium yellow stripe-like 3 (YSL3) transporter localizes to the phloem, transports copper in frog (Xenopus laevis) oocytes, and facilitates copper delivery to reproductive organs and grains. Failure to deliver copper, but not iron, zinc, or manganese to these structures in the ysl3 CRISPR-Cas9 mutant results in delayed flowering, altered inflorescence architecture, reduced floret fertility, grain size, weight, and protein accumulation. These defects are rescued by copper supplementation and are complemented by YSL3 cDNA. This knowledge will help to devise sustainable approaches for improving grain yield in regions where soil quality is a major obstacle for crop production. Copper distribution by a phloem-localized transporter is essential for the transition to flowering, inflorescence architecture, floret fertility, size, weight, and protein accumulation in seeds.

Copper distribution by a phloem-localized transporter is essential for the transition to flowering, inflorescence architecture, floret fertility, size, weight and protein accumulation in seeds.     

Separation of Antioxidant-Rich Alternanthera Sessilis Red Extracts by Sephadex LH-20 and Identification of Polyphenols Using HPLC-QToF-MS/MS

This study aimed to fractionate Alternanthera sessilis Red (ASR) crude extracts and determine their antioxidant activities as well as the related active components in the whole plant. ASR was extracted with water and ethanol, and further separated using a Sephadex LH-20 column. Following the assessments of the polyphenolic contents and antioxidant activities of crude extracts (H₂O_ASR and EtOH_ASR) and fractions, a HPLC-QToF analysis was performed on the crude extracts and selected fractions (H₂O_ASR FII and EtOH_ASR FII). Three water fractions (H₂O_ASR FI, FII and FIII) and four ethanolic fractions (EtOH_ASR FI, FII, FIII and FIV) were derived from their crude extracts, respectively. EtOH_ASR FII exhibited the greatest total phenolic content (120.41 mg GAE/g fraction), total flavonoid content (223.07 mg RE/g fraction), and antioxidant activities (DPPH IC₅₀=159.43 μg/mL; FRAP=1.93 mmol Fe²⁺/g fraction; TEAC=0.90 mmol TE/g fraction). Correlation analysis showed significant (p<0.01) positive correlations between both TPC (r=0.748–0.970) and TFC (r=0.686–0.949) with antioxidant activities in the crude extracts and fractions. Flavonoids were the major compounds in the four selected samples tentatively identified using HPLC-QToF-MS/MS, with the highest number of 30 polyphenol compounds detected in the most active fraction, EtOH_ASR FII.     

Ultrastructure of the male reproductive system and of spermatogenesis in the viviparous brittle-star,Amphipholis squamata

The fine structure of the male reproductive system of the hermaphroditic brittle-star, Amphipholis squamata, has been studied in specimens from both the Pacific coast (Washington) and the Atlantic coast (New Hampshire). Each testis is a small (100-μm) sphere and is attached to the internal wall of the bursa by peritoneal suspensor cells. Occasional flagellated cells are found on the external surface of the testis. The testicular wall of A. squamata is a multilayered structure, similar to that of other ophiuroids, but the hemal sinus is PAS negative in this species. Germinal cells are surrounded throughout their development by the filopodia of interstitial cells. Adjacent interstitial cells are interconnected, and thus form a structural network within the testis. Positionally and functionally, the interstitial cells resemble Sertoli cells; however, their origin, behavior and ultrastructure are different in many ways. Spermatogenesis includes a series of cyclical changes (aspermatogenic phase, proliferative phase, differentiative phase, and evacuative phase). Within a single testis, the resulting production of sperm is in short pulses, but if all 10 testes are taken together, sperm are produced continuously throughout the year. The events of spermiogenesis closely follow those that have been described in other echinoderms. However, we have provided new information on the release of excess cell membranes and the fusion process of mitochondria. The mature spermatozoa of A. squamata are flagellated and motile, and have “primitive” structural features, in spite of the fact that they fertilize the eggs inside the genital bursae. The spermatozoa do not, as was previously thought, enter the bursa by rupture of the adjacent walls. Instead, they are ejaculated through a gonoduct into the rapid incurrent flow of water entering the bursa. The locomotion of the spermatozoa is in eccentric spirals, due to the unusually large angle at which the flagellum is inserted into the base of the sperm.     

Histology of the pedicellariae of the Sand dollar, Dendraster excentricus (Echinodermata)

The pedicellariae in Dendraster excentricus are the bidentate type with a density of 80/cm². There are two distinct size groups; the larger ones measure 0.6 mm long while the small ones are only 0.14 mm. One interesting feature is the fluid of highly sulphated acid mucopolysaccharide in the lumen of the neck. This fluid functions as a hydroskeleton while the flexor muscle operates on it for complicated movement of the neck. The possibility that this fluid is also toxic and so acts as a defence mechanism is discussed. All the muscles involved in the movement of pedicellariae are smooth muscle fibres.     

Designs for a broad substrate specificity keto acid dehydrogenase

Variations have been made to the structure of the nicotinamide adenine dinucleotide (NAD) dependent L-lactate dehydrogenase from Bacillus stearothermophilus at regions of the enzyme that we believe determine specificity toward different alpha-hydroxy acids (RCHOHCOO-, R = CH3, C2H5, etc.). Two regions of LDH that border the active site (but are not involved in the catalytic reaction) were altered in order to accommodate substrates with hydrophobic side chains larger than that of the naturally preferred substrate, pyruvate (R = CH3). The mutations 102-105GlnLysPro----MetValSer and 236-237AlaAla----GlyGly were made to increase the tolerance for large hydrophobic substrate side chains. The triple and double mutants alone gave little improvement for branched-chain-substituted pyruvates. The five changes together produced a broader substrate specificity alpha-hydroxy acid dehydrogenase, with a 55-fold improved kcat for alpha-ketoisocaproate to a value about 1/14 that of the native enzyme for pyruvate. Rational protein engineering enabled coupled changes in enzyme structure to be obtained with greater probability of success than random mutagenesis.