MORERA, S. | bioRxiv Science

bioRxiv2024

Regulation of Arabidopsis polyamine acetylation by NATA1 and NATA2

Polyamines have vital functions in organisms, including bacteria, plants, and animals, with key roles in growth, development, and stress responses. Spermine/spermidine N1-acetyl transferases (SSATs) regulate polyamine abundance by catalysing their N-acetylation, thereby reducing the pool of polyamines and producing other bioactive components. The regulatory mechanisms controlling SSAT enzymes are incompletely understood. Here, we investigate the biological role and regulation of the two SSAT isoforms present in Arabidopsis thaliana, N-ACETYLTRANSFERASE ACTIVITY (NATA) 1 and 2. We show that NATA2 is a heat-stable isoform, induced in response to heat. Intriguingly, a nata2 knockout mutation proved beneficial for growth and pathogen defence under heat stress in Arabidopsis, aligning with the stress-mitigating effect of polyamines. In contrast, the double knockout of nata1 and nata2 was lethal, highlighting the essential role of basal SSAT activity. Our numerous crystal structures of both NATAs, supported by functional assays, revealed that stress-produced acidic metabolites can selectively inhibit polyamine acetylation by occupying the NATA substrate-binding pocket. This environment-responsive regulation mechanism may allow Arabidopsis to adjust the deleterious action of NATAs under stress conditions, without eliminating the enzyme. More generally, metabolite-ensemble inhibition may be a novel paradigm for non-genetic feedback regulation of plant enzymes.

plant biology↗

bioRxiv2022

The antibiotic phazolicin displays a dual mode of uptake in Gram-negative bacteria

Phazolicin (PHZ) is a peptide antibiotic exhibiting narrow-spectrum activity against rhizobia closely related to its producer Rhizobium sp. Pop5. Using genetic and biochemical techniques, we here identified BacA and YejABEF as two importers of PHZ in a sensitive model strain Sinorhizobium meliloti Sm1021. BacA and YejABEF are members of SLiPT and ABC transporter families of non-specific peptide importers, respectively. The uptake of PHZ by two distinct families of transporters dramatically decreases the naturally occurring rate of resistance. Moreover, since both BacA and YejABEF are essential for the development of functional symbiosis of rhizobia with leguminous plants, the acquisition of PHZ resistance via the inactivation of transporters is further disfavoured since single bacA or yejABEF mutants are unable to propagate in root nodules. Crystal structures of the periplasmic subunit YejA from S. meliloti and Escherichia coli revealed fortuitous bound peptides, suggesting a non-specific peptide-binding mechanism that facilitates the uptake of PHZ and other antimicrobial peptides. SIGNIFICANCEMany bacteria produce antimicrobial peptides to eliminate competitors and create an exclusive niche. These peptides kill bacteria by either membrane disruption or inhibiting essential intracellular processes. The Achilles heel of the latter type of antimicrobials is their dependence on transporters to enter the susceptible bacteria since mutations in such transporters result in resistance. We describe here how the ribosome-targeting peptide phazolicin, produced by Rhizobium sp. Pop5, uses two different transporters, BacA and YejABEF, to get into the cells of the symbiotic bacterium Sinorhizobium meliloti. This dramatically reduces the probability of resistance acquisition. Both transporters need to be inactivated for phazolicin resistance acquisition. Since these transporters are also crucial in S. meliloti for its symbiotic association with host plants, their inactivation in biological settings is highly unlikely. This makes PHZ an attractive lead for the development of a biocontrol agent with potential for use in agriculture.

molecular biology↗