Biology subjects

Dann, M.

Publications and source records attributed to Dann, M..

5 recordsLinked to original sources

bioRxiv2026

Multi-omics dissection of transcriptional and post-transcriptional responses in cyanobacterial high-light adaptation

Understanding how photosynthetic organisms acclimate to excess light is essential for the development of robust chassis for synthetic biology approaches aimed at expanding the photosynthetically active absorption spectrum. High-light (HL) tolerant strains were previously generated by laboratory evolution from a laboratory type (LT) strain of Synechocystis sp. PCC 6803, with tolerance attributed to a small number of specific point mutations. Key mutations affected the NDH-1L complex F1-subunit (NdhF1F124L) and translation elongation factor G2 (EF-G2R461C). Reintroduction of these mutations into the LT background was sufficient to confer HL tolerance. However, the mechanisms by which a limited set of point mutations mediates HL tolerance have remained unclear. Here, integrated transcriptomic and proteomic analyses of HL-tolerant strains reveal a coordinated network of responses underlying HL tolerance. The NdhF1F124L mutation increased the accumulation of NDH-1 complex subunits, likely accounting for the previously observed enhancement of cyclic electron flow. In contrast, EF-G2R461C increased the abundance of multiple functional classes of proteins associated with HL tolerance, while post-transcriptionally reducing the level of the phycobilisome linker protein CpcC2, resulting in a decreased antenna size. Integrated analyses further demonstrated that HL tolerance involves transcriptional regulation of protein abundance, including the maintenance of phosphate metabolism. Consistently, overexpression of two genes from the Pho regulon increased HL tolerance. Overall, this study demonstrates how a small number of point mutations in genes with central cellular functions can reprogram the cyanobacterial cell to achieve enhanced tolerance to HL.

evolutionary biology↗

bioRxiv2026

CurT dosage quantitatively affects thylakoid structure and PSII performance in Synechocystis sp. PCC 6803

The photosynthetic thylakoid membrane systems of many oxygenic photosynthesizers form elaborate three-dimensional structures. Curvature Thylakoid (CurT/CURT1) proteins are central regulators of thylakoid architecture in cyanobacteria and plants, driving both grana stacking and the formation of thylakoid convergence zones (TCZs) by promoting membrane curvature while also contributing to cyanobacterial cell and green-algal chloroplast division. While the functional role of grana stacks in terrestrial photosynthesis is well established, the physiological significance of cyanobacterial TCZs remains unclear. Here, we investigated the role of TCZs in Synechocystis sp. PCC 6803 by quantitatively assessing how CurT protein abundance shapes thylakoid membrane organization, TCZ frequency, and thylakoid layering, and how these architectural features relate to photosynthetic efficiency in a set of curT expression mutants. By correlating defined structural parameters of the thylakoid system with cellular CurT levels, we defined for the first time the quantitative relationship between CurT abundance, thylakoid architecture, and photosystem II (PSII) performance. Our results reveal a non-linear, logarithmic relationship: minimal CurT suffices to restore TCZ formation and sustain WT-like growth, while overexpression further enhances PSII activity and culture yield. Together, these findings identify CurT as a dose-dependent key determinant of thylakoid structure and underscore the functional importance of thylakoid membrane architecture for efficient photosynthesis. Significance StatementThis study assesses how the membrane-shaping protein CurT quantitatively regulates thylakoid architecture and photosynthetic performance in the model cyanobacterium Synechocystis sp. PCC 6803. By relating CurT abundance to the formation of thylakoid convergence zones, photosystem II efficiency, and growth rate, we provide evidence of CurT acting as a key regulator of cyanobacterial membrane organization in a dosage-dependent manner. Our findings provide insight into the structural basis and physiological relevance of thylakoid convergence zones and suggest CurT as a potential target for improving cyanobacterial light-energy conversion.

microbiology↗

bioRxiv2025

High-light adaptation in Synechocystis by accumulating NDH proteins and depleting specific phycobilisome linker proteins

Photosynthetic organisms have evolved mechanisms to manage excess light, crucial for maximizing photosynthetic efficiency. High-light (HL) tolerant Synechocystis sp. PCC6803 strains were developed through laboratory evolution, with tolerance attributed to specific point mutations. Key mutations affected the NDH-1L complex F1-subunit (NdhF1F124L) and translation elongation factor G2 (EF-G2R461C). Reintroducing these mutations into laboratory strains conferred HL tolerance. Comparisons with knockout and overexpressor lines showed NdhF1F124L and EF-G2R461C result in gain of function. Transcriptomic and proteomic analysis unveiled a network of responses contributing to HL tolerance, including maintenance of phosphate metabolism and decreased antenna size by depleting a specific linker protein in EF-G2R461C cells. Consequently, overexpression of Pho regulon genes increased HL tolerance. NdhF1F124L enhances cyclic electron flow (CEF) by increasing NDH-1 complex subunit accumulation. Other HL-adapted strains demonstrated that increased CEF and decreased antenna size are recurring outcomes, achievable through various mutations. This study demonstrates how limited mutations can reconfigure cells for enhanced HL tolerance, offering insights for improving photosynthetic efficiency.

physiology↗

bioRxiv2025

Improving tolerance to fluctuating light through adaptive laboratory evolution in the cyanobacterium Synechocystis

Fluctuating light (FL) poses a serious challenge to photosynthetic organisms like cyanobacteria, disrupting carbon assimilation and damaging photosystems. While key components of cyanobacterial FL tolerance have been identified, their genetic enhancement remains unexplored. We applied adaptive laboratory evolution to Synechocystis PCC 6803 under two complex FL regimes, including one lethal to the starter strain (LT), to generate FL-adaptive alleles. Our analysis revealed 44 fully segregated novel mutations in 24 monoclonal evolved strains, 28 of which affected proteins or structural RNAs. We focused on three mutations for further study. Mutations in Pam68, involved in photosystem II (PSII) assembly, and Sll0518 were present in all evolved strains, indicating early emergence. These mutations increased tolerance to non-lethal FL conditions when introduced into LT, with the Pam68 mutation possibly protecting PSI by increasing the proportion of less active PSII monomers. A gain-of-function mutation in RpaB, regulator of phycobilisome association B, was found in three strains tolerant to lethal FL. When introduced into LT, this mutation significantly increased tolerance to both lethal FL and high light conditions, associated with downregulation of photosystem accumulation and light harvesting. As RpaB has plant homologs, this finding could potentially be used to improve agricultural productivity under variable light conditions.

evolutionary biology↗

bioRxiv2017

Mutation rates in seeds and seed-banking influence substitution rates across the angiosperm phylogeny

1) BackgroundSeed-banking (the ability to persist in the soil over many generations) is usually considered as a dormant stage where genotypes are \"stored\" as a bet-hedging strategy in response to unpredictable environments. However, seed dormancy may instead have consequences for the integrity of the DNA and generate novel mutations.\n\n2) MethodsWe address this paradox by building phylogenies based on the plastomes and nuclear ITS of species belonging to ten angiosperm clades. In each clade, the substitution rate (branch-length) of a seed-banking species is compared with that of a closely-related non-seed-banking species.\n\n3) ResultsSeed-banking species show as high or higher substitution rates than non-seedbanking species, and therefore mutations occur in dormant seeds at a rate at least as high as in above-ground plants. Moreover, seed born mutations have the same probability to reach fixation as those from above ground. Our results are robust to differences in selection, generation time, and polymorphism.\n\n4) ConclusionsMutations occurring in seeds, and thus seed-banking, affect the population diversity of plant species, and are observable at the macro-evolutionary scale. Our study has consequences for seed storage projects, since the stored seeds are likely to accumulate mutations at a higher rate than previously thought.

evolutionary biology↗