Satoh, H. | bioRxiv Science

bioRxiv2025

The protective role of chloroplast NADH dehydrogenase-like complex (NDH) against PSI photoinhibition under chilling stress

Chilling stress induces photosystem I (PSI) photoinhibition in various plants, severely impairing their growth. However, the mechanisms suppressing chilling-induced PSI photoinhibition remain unclear. This study aimed to identify factors preventing PSI photoinhibition by comparing two cucumber cultivars with different susceptibilities to PSI photoinhibition and chilling stress tolerance. In the chilling-sensitive cultivar, partial degradation of the CF1-{gamma} subunit of chloroplast ATPase led to uncoupling of the thylakoid membrane. In addition, electron efflux from Fe-S clusters downstream of PSI was restricted under chilling stress, resulting in highly reduced Fe-S clusters. Notably, this PSI over-reduction in the chilling-sensitive cultivar was observed not only under chilling stress but also under fluctuating light conditions, limited CO2 conditions, and during the transition from darkness to light, suggesting that cyclic electron flow contributes to cultivar differences in PSI photoinhibition. Indeed, the chilling-tolerant cultivar exhibited higher activity of the chloroplast NADH dehydrogenase-like complex (NDH) and suppressed reactive oxygen species (ROS) accumulation during the early stages of chilling stress. In contrast, in the chilling-sensitive cultivar, destabilization of PSI-NDH supercomplex under chilling stress led to the loss of NDH activity, resulting in severe PSI over-reduction. This study provides evidence that NDH acts as a crucial electron sink to prevent PSI photoinhibition and provides new insights into the mechanisms underlying low-temperature stress tolerance.

plant biology↗

bioRxiv2023

Microscopic and metatranscriptomic analyses revealed unique cross-domain symbiosis between Candidatus Patescibacteria/candidate phyla radiation (CPR) and methanogenic archaea in anaerobic ecosystems

To verify the parasitic lifestyle of Candidatus Patescibacteria in the enrichment cultures derived from a methanogenic bioreactor, we applied multifaceted approaches combining cultivation, microscopy, metatranscriptomic, and protein structure prediction analyses. Cultivation experiments with the addition of exogenous methanogenic archaea with acetate, amino acids, and nucleoside monophosphates and 16S rRNA gene sequencing confirmed the increase in the relative abundance of Ca. Patescibacteria and methanogens. The predominant Ca. Patescibacteria were Ca. Yanofskybacteria and 32-520 lineages (to which belongs to class Ca. Paceibacteria) and positive linear relationships (r2 [≥] 0.70) between the relative abundance of Ca. Yanofskybacteria and Methanothrix, suggesting that the tendency of the growth rate is similar to that of the host. By fluorescence in situ hybridization (FISH) observations, the FISH signals of Methanothrix and Methanospirillum cells with Ca. Yanofskybacteria and with 32-520 lineages, respectively, were significantly lower than those of the methanogens without Ca. Patescibacteria, suggesting their parasitic interaction. The TEM and SEM observations also support parasitism in that the cell walls and plugs of these methanogens associated with submicron cells were often deformed. In particular, some Methanothrix-like filamentous cells were dented where the submicron cells were attached. Metatranscriptomic and protein structure prediction analyses identified highly expressed secreted genes from the genomes of Ca. Yanofskybacteria and 32-520, and these genes contain adhesion-related domains to the host cells. Considering the results through the combination of microscopic observations, gene expression, and computational protein modeling, we propose that the interactions between Ca. Yanofskybacteria and 32-520 belonging to class Ca. Paceibacteria and methanogenic archaea are parasitism.

microbiology↗