Soufi, Z. | bioRxiv Science

bioRxiv2025

Assembly of two functionally-distinct protein import complexes in the outer membrane of plant chloroplasts

The TOC translocon delivers thousands of nucleus-encoded proteins to chloroplasts and related non-photosynthetic plastids. It comprises the {beta}-barrel channel, Toc75, and multiple isoforms of receptor GTPases, Toc33 and Toc159. However, exactly how TOC complexes are assembled in different plastid types is unknown. Here, we present detailed characterization of two distinct TOC complexes, TOC-P and TOC-N, from photosynthetic chloroplasts and non-photosynthetic plastids, respectively. The assembled complexes are distinguished by having different sets of receptors, but both possess Toc75 which we identify as a central hub in TOC biogenesis: assembly is driven by TOC75 expression, with the Toc33 and Toc159 being added sequentially thereafter. Integrative structural analysis revealed a modular architecture for TOC-P comprising a cytosolic GTPase receptor module linked flexibly to a membrane {beta}-barrel channel module. TOC-N has a similar overall architecture, albeit with some clear differences that likely account for observed functional differences related to client specificity.

cell biology↗

bioRxiv2020

RpoS Contributes to Successful Opportunistic Colonization by Human Enteric Pathogens during Plant Disease

With an increase in foodborne illnesses associated with the consumption of fresh produce, it is important to understand the interactions between human bacterial enteric pathogens and plants. It was previously established that diseased plants can create a permissive environment for opportunistic endophytic colonization of enteric pathogens. However, the factors that contribute to the colonization of enteric pathogens during plant disease are largely unknown. Here, we show that both strain and plant host factors contribute to significantly increased populations of enteric pathogens when co-inoculated with the plant pathogen, P. syringae pv. tomato. The two Salmonella enterica strains DM10000 and 14028S, differ in their ability to metabolize host-derived apoplastic carbohydrates dependent on the sigma factor RpoS. The rpoS gene is an important strain factor for endophytic colonization by S. enterica during plant disease. Our results suggest that rpoS plays a crucial role during in planta colonization, balancing nutrient metabolism and stress responses. ImportanceFoodborne illnesses caused by the bacterial human enteric pathogens, E. coli O157:H7 and S. enterica, often results in vomiting and diarrhea. If left untreated, this illness can cause dehydration and sometimes death of a patient. Both E. coli O157:H7 and S. enterica have caused repeated fresh produce-associated epidemics. Crop disease could promote the ability of plants to act as reservoirs for produce-borne outbreaks. Plant pathogens dampen plant immunity, which allows for a more permissive environment for human enteric pathogens to grow. These internalized enteric pathogen populations are especially dangerous since they cannot be removed by washing alone. Therefore, the need to understand the factors that contribute to the opportunistic colonization of human enteric pathogens during plant disease is apparent. Our research has identified host and strain factors that contribute to opportunistic colonization of diseased plants, which will inform the development of future management strategies to mitigate future outbreaks.

pathology↗