Soil fungal communities differ between shaded and sun-intensive coffee plantations in El Salvador.

Coffea arabica is a highly traded commodity worldwide, and its plantations are habitat to a wide range of organisms. Coffee farmers are shifting away from traditional shade coffee farms in favor of sun-intensive, higher yield farms, which can impact local biodiversity. Using plant-associated microorganisms in biofertilizers, particularly fungi collected from local forests, to increase crop yields has gained traction among coffee producers. However, the taxonomic and spatial distribution of many fungi in coffee soil, nearby forests and biofertilizers is unknown. We collected soil samples from a sun coffee system, shade coffee system, and nearby forest from Izalco, Sonsonate, El Salvador. At each coffee system, we collected soil from the surface (upper) and 10 cm below the surface (lower), and from the coffee plant drip line (drip line) and the walkway between two plants (walkway). Forest soils were collected from the surface only. We used ITS metabarcoding to characterize fungal communities in soil and in the biofertilizer (applied in both coffee systems), and assigned fungal taxa to functional guilds using FUNGuild. In the sun and shade coffee systems, we found that drip line soil had higher richness in pathotrophs, symbiotrophs, and saprotrophs than walkway soil, suggesting that fungi select for microhabitats closer to coffee plants. Upper and lower soil depths did not differ in fungal richness or composition, which may reflect the shallow root system of Coffea arabica. Soil from shade, sun, and forest had similar numbers of fungal taxa, but differed dramatically in community composition, indicating that local habitat differences drive fungal species sorting among systems. Yet, some fungal taxa were shared among systems, including seven fungal taxa present in the biofertilizer. Understanding the distribution of coffee soil mycobiomes can be used to inform sustainable, ecologically friendly farming practices and identify candidate plant-growth promoting fungi for future studies.

Interaction between the AAA+ ATPase p97 and its cofactor ataxin3 in health and disease: Nucleotide-induced conformational changes regulate cofactor binding.

p97 is an essential ATPase associated with various cellular activities (AAA+) that functions as a segregase in diverse cellular processes, including the maintenance of proteostasis. p97 interacts with different cofactors that target it to distinct pathways; an important example is the deubiquitinase ataxin3, which collaborates with p97 in endoplasmic reticulum-associated degradation. However, the molecular details of this interaction have been unclear. Here, we characterized the binding of ataxin3 to p97, showing that ataxin3 binds with low-micromolar affinity to both wild-type p97 and mutants linked to degenerative disorders known as multisystem proteinopathy 1 (MSP1); we further showed that the stoichiometry of binding is one ataxin3 molecule per p97 hexamer. We mapped the binding determinants on each protein, demonstrating that ataxin3's p97/VCP-binding motif interacts with the inter-lobe cleft in the N-domain of p97. We also probed the nucleotide dependence of this interaction, confirming that ataxin3 and p97 associate in the presence of ATP and in the absence of nucleotide, but not in the presence of ADP. Our experiments suggest that an ADP-driven downward movement of the p97 N-terminal domain dislodges ataxin3 by inducing a steric clash between the D1-domain and ataxin3's C terminus. In contrast, MSP1 mutants of p97 bind ataxin3 irrespective of their nucleotide state, indicating a failure by these mutants to translate ADP binding into a movement of the N-terminal domain. Our model provides a mechanistic explanation for how nucleotides regulate the p97-ataxin3 interaction and why atypical cofactor binding is observed with MSP1 mutants.