Kell, T. | bioRxiv Science

bioRxiv2026

Prion-like domains control plastid targeting of PEPSI effectors and PEPSI6-mediated modulation of DXR during root symbiosis

Microbial effectors often act in the apoplast or cytosol, but how they reach host organelles during beneficial plant-fungal interactions remains poorly understood. Here, we identify a class of secreted prion-like effector proteins from the mutualistic root endophyte Serendipita indica, termed PEPSIs. These proteins contain prion-like domains (PrLDs) embedded within intrinsically disordered regions, and three tested PEPSIs require these domains for plastid localization. Focusing on PEPSI6, we show that plastid targeting depends on its PrLD and is associated with engagement of plastid import and proteostasis machinery. In plastids, PEPSI6 associates with 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR), promotes DXR accumulation, alters methylerythritol phosphate pathway metabolites, and enhances tolerance to the DXR inhibitor fosmidomycin. PEPSI6 also undergoes apoplastic C-terminal CAP-domain processing, and its colonization-promoting activity persists after PrLD deletion, indicating a plastid-targeting-independent function. Overall, this work identifies PrLDs as noncanonical plastid-targeting elements in PEPSI effectors and reveals DXR as a target of fungal manipulation during root symbiosis. HighlightsO_LIPrion-like domains control plastid targeting of selected PEPSI effectors. C_LIO_LIPEPSI6 associates with DXR and promotes its accumulation in plastids. C_LIO_LIPEPSI6 alters MEP-pathway metabolites and increases tolerance to fosmidomycin. C_LIO_LIApoplastic processing reveals a plastid-independent PEPSI6 activity during root symbiosis. C_LI

plant biology↗

bioRxiv2024

The Drosophila tyramine-beta-hydroxylase gene encodes multiple isoforms with different functions

The Tyramine-beta-hydroxylase (Tbh) is required for octopamine synthesis. To better understand the function of Tbh in neurotransmitter synthesis, we analyzed the molecular genetic organization of the Drosophila melanogaster Tbh gene and found that the Tbh gene encodes multiple transcripts. The transcripts differ in their 5UTR, which results in proteins that differ in their size and putative phosphorylation sites, suggesting that the Tbh function is regulated at translational and posttranslational levels. We generated a new Tbh mutant - TbhDel3 - using FLP/FRT recombination mutagenesis to remove the translational start site still that is present in TbhnM18mutants. The TbhDel3 mutants share ethanol tolerance and larval locomotion defects with the TbhnM18 mutants. But, they differ in terms of their cellular stress response. To develop normal levels of ethanol tolerance, Tbh is required in a subset of Tbh expressing neurons in the adult brain, which was identified using a newly generated Tbh-Gal4 driver. Taking advantage of a newly generated Tbh antibody serum, we show that one Tbh isoform is expressed in a group of peptidergic Hugin-positive and noradrenergic neurons uncoupling Tbh function from octopamine synthesis. The existence of different functional Tbh isoforms impacts our understanding of the regulatory mechanisms of neurotransmitter synthesis and the function of the octopaminergic neurotransmitter system in cellular processes and the regulation of behavior. Author SummaryVertebrates and insects have structurally identical signaling molecules in their nervous system, such as the neurotransmitter dopamine. But, there are also neurotransmitters that are thought to only occur in the vertebrate or insect brain. Noradrenaline is one such neurotransmitter that regulates flight and fight responses in vertebrates. In insects such as the fruit fly Drosophila melanogaster, the structurally very similar neurotransmitter octopamine is considered to be an invertebrate-specific neurotransmitter that performs similar functions to noradrenaline. The functional similarities also extend to enzymes required for synthesis. Our analysis shows that the enzyme for octopamine synthesis exists in several variations and that the connection between the enzymes and the synthesized neurotransmitter may not be as simple as presumed. Exploiting molecular, behavioral and neuroanatomical studies, we show that different variants might be used in response to different environmental conditions and/or the synthesis of alternative, structurally similar neurotransmitters, such as noradrenaline. These results challenge our view on the functions of octopamine and noradrenaline in the regulation of behavior.

neuroscience↗