Biology subjects

Baeumers, M.

Publications and source records attributed to Baeumers, M..

3 recordsLinked to original sources

bioRxiv2026

Arabidopsis GLK transcription factors interact with ABI4 to modulate cotyledon greening in light-exposed etiolated seedlings

During seedling etiolation in darkness, the biosynthesis of protochlorophyllide (Pchlide) and the development of etioplasts must be strictly controlled to prevent photooxidative damage upon light exposure. The transcription factors GLK1 and GLK2 are central regulators of chlorophyll biosynthesis and chloroplast biogenesis. Here, we show that GLK1 and GLK2 interact with ABSCISIC ACID INSENSITIVE 4 (ABI4). We reveal that GLKs and ABI4 have antagonistic functions in cotyledon greening of light-exposed etiolated seedlings: compared to the wild type, abi4 mutants, similar to a transgenic line overexpressing GLK2, accumulated more Pchlide in dark-grown seedlings, while glk1 glk2 mutants contained less Pchlide. The high Pchlide levels in etiolated abi4 mutants and GLK2 overexpressors were inefficiently photoreduced upon light exposure, leading to a significant accumulation of 1O2 in the cotyledons after the dark-to-light transition. This corresponded to low cotyledon greening rates and low seedling survival. Additionally, we identified eight PhANGs involved in Pchlide biosynthesis and etioplast development, whose transcript accumulation patterns may contribute to the photobleaching of etiolated abi4 mutants and GLK2 overexpressors. Importantly, the high Pchlide content, low cotyledon greening rate, high 1O2 level and high PhANG induction in abi4 mutant seedlings were fully dependent on GLK1 and GLK2, indicating that ABI4 acts upstream of GLKs. Since ABI4 does not regulate GLK transcript level, and ABI4 physically interacts with GLK proteins, these data suggest that ABI4 inhibits GLK1 and GLK2 activities in etiolated seedlings to prevent high Pchlide accumulation which would lead to high 1O2 levels and seedling death upon exposure to light. Significance statementThe transition from darkness to light is a critical moment that determines seedling establishment and survival. We report here that the transcription factor ABI4 inhibits GLK1 and GLK2 activities during seedling etiolation to repress Pchlide biosynthesis in darkness, thereby limiting singlet oxygen accumulation and seedling death upon exposure to light.

plant biology↗

bioRxiv2025

Differentiation of Xanthomonas oryzae pv. oryzae in vitro and during rice leaf infection

Highlights- Xoo produces filamentous morphology, which is transient and yields pleomorphic progenies in vitro - In planta, initial attachment of rod-shaped Xoo is detected at xylem pits - The Xoo infection front migrates basipetally in the vascular bundle and progresses laterally from major to minor veins via transverse veins - Xoo breaks out of the xylem vessels and enter the neighboring xylem parenchyma - Xoo assumes filamentous morphology that can traverse from the xylem across the bundle sheath into mesophyll tissue - Mobility in xylem vessels depends predominantly on rod-shaped Xoo, while infection of mesophyll tissue at later stages appears to be linked to filamentous morphology SummaryXanthomonas oryzae pv. oryzae (Xoo) is classified as a xylem pathogen responsible for bacterial blight of rice causing substantial yield losses in Asia and Africa. Xoo virulence depends on the ability to trigger SWEET sucrose efflux transporters in the xylem parenchyma (XP) by injection of transcription activation like effectors (TALe) into host cells, likely to access host-derived sucrose. To establish infection, Xoo must overcome physical barriers, immune responses and the hydraulic xylem flow. To gain insights into the colonization process, we used translational SWEET11a-GUS reporter lines, scanning electron microscopy, and confocal laser scanning microscopy of Xoo tagged with a fluorescent protein. We found that Xoo can differentiate in vitro into filamentous forms. We mapped the infection route of Xoo along the vasculature, identified distinct spatiotemporal phases of Xoo colonization marked by rod-shaped and, notably, filamentous Xoo cells. Rod-shaped Xoo were found to attach to xylem pits during basipetal progression of the infection. Notably, we found that at later infection stages, Xoo could enter the XP. Strikingly, Xoo adopted a filamentous phenotype that traversed bundle sheath cells and entered mesophyll cells. Chlorosis and necrosis of leaves is thus likely not just due to blockage of xylem flow, but to direct tissue damage. Filamentation had been reported as important for virulence of human pathogens e.g. Yersinia pestis, uropathogenic E. coli and Shigella and had been associated to sugar utilization in Bacillus subtilis. We thus hypothesize that Xoo differentiation during host colonization is critical for virulence. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/680524v1_ufig1.gif" ALT="Figure 1"> View larger version (48K): org.highwire.dtl.DTLVardef@f66d8borg.highwire.dtl.DTLVardef@91ca66org.highwire.dtl.DTLVardef@17f2846org.highwire.dtl.DTLVardef@12d46e7_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2022

The periplasmic chaperone Skp prevents misfolding of the secretory lipase A from Pseudomonas aeruginosa

Pseudomonas aeruginosa is a wide-spread opportunistic human pathogen and a high-risk factor for immunodeficient people and patients with cystic fibrosis. The extracellular lipase A belongs to the virulence factors of P. aeruginosa. The lipase undergoes folding and activation in the periplasm prior the secretion. Here, we demonstrate that the ubiquitous periplasmic chaperone Skp of P. aeruginosa, but not SurA, FkpA, PpiD or YfgM, efficiently prevents misfolding of the aggregation-prone lipase A and facilitates its activation by a specific foldase LipH. Small-angle X-ray scattering visualizes the trimeric architecture of P. aeruginosa Skp and identifies two primary conformations of the chaperone, a compact and a widely open. We describe two binding modes of Skp to the lipase, with affinities of 20 nM and 2 M, which correspond to 1:1 and 1:2 stoichiometry of the lipase:Skp complex. Two Skp trimers are required to stabilize the lipase via the apolar interactions, which are not affected by high salt concentrations typical for the sputum of cystic fibrosis patients. The chaperoning effect of Skp points to its potent role in maturation and secretion of the lipase in Pseudomonas species.

biochemistry↗