SEL1L-HRD1 interaction is required to form a functional HRD1 ERAD complex.

The SEL1L-HRD1 protein complex represents the most conserved branch of endoplasmic reticulum (ER)-associated degradation (ERAD). Despite recent advances in both mouse models and humans, in vivo evidence for the importance of SEL1L in the ERAD complex formation and its (patho-)physiological relevance in mammals remains limited. Here we report that SEL1L variant p.Ser658Pro (SEL1LS658P) is a pathogenic hypomorphic mutation, causing partial embryonic lethality, developmental delay, and early-onset cerebellar ataxia in homozygous mice carrying the bi-allelic variant. Biochemical analyses reveal that SEL1LS658P variant not only reduces the protein stability of SEL1L, but attenuates the SEL1L-HRD1 interaction, likely via electrostatic repulsion between SEL1L F668 and HRD1 Y30 residues. Proteomic screens of SEL1L and HRD1 interactomes reveal that SEL1L-HRD1 interaction is a prerequisite for the formation of a functional HRD1 ERAD complex, as SEL1L is required for the recruitment of E2 enzyme UBE2J1 as well as DERLIN to HRD1. These data not only establish the disease relevance of SEL1L-HRD1 ERAD, but also provide additional insight into the formation of a functional HRD1 ERAD complex.

Characterizing the development of photosynthetic capacity in relation to chloroplast structure and mineral nutrition in leaves of three woody fruit species.

Plants have evolved different developmental patterns of photosynthetic capacity to better adapt to changing environmental conditions. Natural variation in photosynthetic development offers great potential for improving crop productivity. In this study, leaf developmental patterns were characterized in three woody fruit tree species with distinct photosynthetic capacity and growth habits. Changes in the photosynthetic rate, photosystem II (PSII) efficiency, chloroplast ultrastructure, activities of photosynthetic enzymes, and contents of carbohydrates and mineral nutrients were examined at five developmental stages to explore the interspecific variation in photosynthetic development. Rapid development of photosynthetic machinery and high photosynthetic capacity were found in Indian jujube (Ziziphus mauritiana) and apple (Malus domestica), whose net CO2 assimilation rate (A) peaked at full leaf expansion (FLE). Litchi (Litchi chinensis), a delayed-greening species, showed slow development of photosynthetic competence, with A peaked after FLE. The low photosynthetic capacity of litchi during early leaf expansion was associated with its delayed chloroplast development, low accumulation of starch, and low activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and NADP-glyceraldehyde-3-phosphate dehydrogenase. Correlations between mineral contents and A across leaf stages and species identified manganese as the rate-limiting nutrients in photosynthetic development in new leaves. Foliar spray of MnSO4 solution (1 g l-1) induced a short-term increase in photosynthesis in young leaves of litchi. These findings suggest that a better understanding of interspecific variation in photosynthetic development facilitates the development of new strategies for improving the photosynthetic efficiency of woody fruit trees.

A Temperature-Sensitive Misfolded bri1-301 Receptor Requires Its Kinase Activity to Promote Growth.

BRASSINOSTEROID-INSENSITIVE1 (BRI1) is a leucine-rich-repeat receptor-like kinase that functions as the cell surface receptor for brassinosteroids (BRs). Previous studies showed that BRI1 requires its kinase activity to transduce the extracellular BR signal into the nucleus. Among the many reported mutant bri1 alleles, bri1-301 is unique, as its glycine-989-to-isoleucine mutation completely inhibits its kinase activity in vitro but only gives rise to a weak dwarf phenotype compared with strong or null bri1 alleles, raising the question of whether kinase activity is essential for the biological function of BRI1. Here, we show that the Arabidopsis (Arabidopsis thaliana) bri1-301 mutant receptor exhibits weak BR-triggered phosphorylation in vivo and absolutely requires its kinase activity for the limited growth that occurs in the bri1-301 mutant. We also show that bri1-301 is a temperature-sensitive misfolded protein that is rapidly degraded in the endoplasmic reticulum and at the plasma membrane by yet unknown mechanisms. A temperature increase from 22°C to 29°C reduced the protein stability and biochemical activity of bri1-301, likely due to temperature-enhanced protein misfolding. The bri1-301 protein could be used as a model to study the degradation machinery for misfolded membrane proteins with cytosolic structural lesions and the plasma membrane-associated protein quality-control mechanism.

Toughening polylactide with polyether-block-amide and thermoplastic starch acetate: Influence of starch esterification degree.

Native corn starch was esterified with acetic anhydride and plasticized with glycerol to give the thermoplastic starch acetate (TPSA). TPSA was blended with polylactide (PLA) and polyether-block-amide-graft-glycidyl methacrylate (PEBA-g-GMA) to obtain biodegradable PLA/PEBA-g-GMA/TPSA blends with high notched impact resistance and low cost. Compared with PLA/PEBA-g-GMA blends, as much as 9 wt% expensive PEBA-g-GMA elastomer could be substituted by the slightly acetylated thermoplastic starch while retaining high impact strength. The mechanical properties depended on the esterification degree of starch acetate. The impact strength, tensile strength and elongation at break increased to the peak value with increasing the esterification degree from 0 to 0.04, thereafter they decreased on further increasing the esterification degree. The morphological results showed that the TPSA particles were smaller and more uniform at the optimum esterification degree of 0.04, leading to the peak value of the mechanical properties.