Curvature thylakoid 1 proteins modulate prolamellar body morphology and promote organized thylakoid biogenesis in Arabidopsis thaliana.

The term "de-etiolation" refers to the light-dependent differentiation of etioplasts to chloroplasts in angiosperms. The underlying process involves reorganization of prolamellar bodies (PLBs) and prothylakoids into thylakoids, with concurrent changes in protein, lipid, and pigment composition, which together lead to the assembly of active photosynthetic complexes. Despite the highly conserved structure of PLBs among land plants, the processes that mediate PLB maintenance and their disassembly during de-etiolation are poorly understood. Among chloroplast thylakoid membrane-localized proteins, to date, only Curvature thylakoid 1 (CURT1) proteins were shown to exhibit intrinsic membrane-bending capacity. Here, we show that CURT1 proteins, which play a critical role in grana margin architecture and thylakoid plasticity, also participate in de-etiolation and modulate PLB geometry and density. Lack of CURT1 proteins severely perturbs PLB organization and vesicle fusion, leading to reduced accumulation of the light-dependent enzyme protochlorophyllide oxidoreductase (LPOR) and a delay in the onset of photosynthesis. In contrast, overexpression of CURT1A induces excessive bending of PLB membranes, which upon illumination show retarded disassembly and concomitant overaccumulation of LPOR, though without affecting greening or the establishment of photosynthesis. We conclude that CURT1 proteins contribute to the maintenance of the paracrystalline PLB morphology and are necessary for efficient and organized thylakoid membrane maturation during de-etiolation.

Antimicrobial solid media for screening non-sterile Arabidopsis thaliana seeds.

Stable genetic transformation of plants is a low-efficiency process, and identification of positive transformants usually relies on screening for expression of a co-transformed marker gene. Often this involves germinating seeds on solid media containing a selection reagent. Germination on solid media requires surface sterilization of seeds and careful aseptic technique to prevent microbial contamination, but surface sterilization techniques are time consuming and can cause seed mortality if not performed carefully. We developed an antimicrobial cocktail that can be added to solid media to inhibit bacterial and fungal growth without impairing germination, allowing us to bypass the surface sterilization step. Adding a combination of terbinafine (1 µM) and timentin (200 mg l-1 ) to Murashige and Skoog agar delayed the onset of observable microbial growth and did not affect germination of non-sterile seeds from 10 different wild-type and mutant Arabidopsis thaliana accessions. We named this antimicrobial solid medium "MSTT agar". Seedlings sown in non-sterile conditions could be maintained on MSTT agar for up to a week without observable contamination. This medium was compatible with rapid screening methods for hygromycin B, phosphinothricin (BASTA) and nourseothricin resistance genes, meaning that positive transformants can be identified from non-sterile seeds in as little as 4 days after stratification, and transferred to soil before the onset of visible microbial contamination. By using MSTT agar we were able to select genetic transformants on solid media without seed surface sterilization, eliminating a tedious and time-consuming step.

Synthetic Protein Scaffolding at Biological Membranes.

Protein scaffolding is a natural phenomenon whereby proteins colocalize into macromolecular complexes via specific protein-protein interactions. In the case of metabolic enzymes, protein scaffolding drives metabolic flux through specific pathways by colocalizing enzyme active sites. Synthetic protein scaffolding is increasingly used as a mechanism to improve product specificity and yields in metabolic engineering projects. To date, synthetic scaffolding has focused primarily on soluble enzyme systems, but many metabolic pathways for high-value secondary metabolites depend on membrane-bound enzymes. The compositional diversity of biological membranes and general challenges associated with modifying membrane proteins complicate scaffolding with membrane-requiring enzymes. Several recent studies have introduced new approaches to protein scaffolding at membrane surfaces, with notable success in improving product yields from specific metabolic pathways.