Biology subjects

Napier, R. M.

Publications and source records attributed to Napier, R. M..

3 recordsLinked to original sources

bioRxiv2022

Polymer nanoparticles pass the plant interface

As agriculture strives to feed an ever-increasing number of people, it must adapt to cope with climate change. It is also clear that our biosphere is suffering from an increasing burden of anthropogenic waste which includes minute plastic particles. It is not yet known whether plants will accumulate such micro- and nanoplastic materials, nor how their surface properties might influence uptake. Therefore, we prepared well-defined block copolymer nanoparticles with a range of different sizes (Dh = 20 - 100 nm) and surface chemistries by aqueous dispersion polymerisation using different functional macro chain transfer agents. A BODIPY fluorophore was then incorporated via hydrazone formation and uptake of these fluorescent nanoparticles into intact roots and protoplasts of Arabidopsis thaliana was investigated using confocal microscopy. Where uptake was seen, it was inversely proportional to nanoparticle size. Positively charged particles accumulated around root surfaces and were not taken up by roots or protoplasts, whereas negatively charged nanoparticles accumulated slowly in protoplasts and roots, becoming prominent over time in the xylem of intact roots. Neutral nanoparticles exhibited early, rapid penetration into plant roots and protoplasts, but lower xylem loads relative to the negative nanoparticles. These behaviours differ from those recorded in animal cells and our results show that, despite robust cell walls, plants are vulnerable to nanoplastic particles in the water and soil. The data form both a platform for understanding plastic waste in the farmed environment, and may also be used constructively for the design of precision delivery systems for crop protection products. Significance StatementSustainable food production must keep pace with the growing global population, as well as adapt to climate change and other anthropogenic insults. It has become clear that micro-and nanoscale plastics are accumulating in all parts of the biosphere and we have set out to study how vulnerable plants are to such waste. We show that the size and surface properties of the designed plastics significantly affect both their speed of uptake and distribution within intact roots. Crucially, it is clear that rigid cell walls around plant cells are no barrier to the smallest particles and these pass into the plants vasculature. Our results relate to plastic waste but can also be used to develop precision vehicles for crop protection.

plant biology↗

bioRxiv2021

NON-SPECIFIC EFFECTS OF A CINNAMATE-4-HYDROXYLASE INHIBITOR ON AUXIN HOMEOSTASIS

Chemical inhibitors are often implemented for the functional characterization of genes to overcome the limitations associated with genetic approaches. Although being a powerful tool, off-target effects of these inhibitors are easily overlooked in a complex biological setting. Here we illustrate the implications of such secondary effects by focusing on piperonylic acid (PA), an inhibitor of CINNAMATE-4-HYDROXYLASE (C4H) that is often used to investigate the involvement of lignin during plant growth and development. When supplied to plants, we found that PA is recognized as a substrate by GRETCHEN HAGEN 3.6 (GH3.6), an amido synthetase involved in the formation of the auxin catabolite indole-3-acetic acid (IAA)-Asp. By competing for the same enzyme, PA interferes with auxin conjugation, resulting in an increase in cellular auxin concentrations. These increased auxin levels likely further contribute to an increase in adventitious rooting previously observed upon PA-treatment. Despite the focus on GH3.6 in this report, PA is conjugated by an array of enzymes and their subsequent reduced activity on native substrates could potentially affect a whole set of physiological processes in the plant. We conclude that surrogate occupation of the endogenous conjugation machinery in the plant by exogenous compounds is likely a more general phenomenon that is rarely considered in pharmacological studies. Our results hereby provide an important basis for future reference in studies using chemical inhibitors.

plant biology↗

bioRxiv2019

A fuzzy encounter complex precedes formation of the fully-engaged TIR1-Aux/IAA auxin co-receptor system

The plant hormone auxin regulates almost every aspect of plant development via the TIR1/AFB-auxin-Aux/IAA auxin co-receptor complex. Within this ternary complex, auxin acts as a molecular glue to promote the binding of Aux/IAA transcriptional repressor proteins to SCFTIR1/AFB ubiquitin-ligase complexes, thereby catalysing their ubiquitin-mediated proteolysis. A conspicuous feature of the crystal structure of the complex is a rare cis W-P bond within the Aux/IAA degron motif. To study receptor complex assembly, we have used NMR to determine the solution structure of the amino-terminal half of the Aux/IAA protein AXR3/IAA17, including the degron, both in isolation and in complex with TIR1 and auxin. We show that this region of AXR3 is intrinsically-disordered with only limited elements of structure and yet the critical degron W-P bond occurs with an unusually high (1:1) ratio of cis to trans isomers. We show that assembly of the co-receptor complex involves both auxin-dependent and -independent interaction events in which the disorder of the Aux/IAA is retained. Further, using the synthetic auxin molecule cvxIAA and by analysing specific Aux/IAA conformers, we show that a subset of auxin-dependent binding events occur away from the base of the canonical auxin binding pocket in TIR1. Our results reveal the existence of a fuzzy, topologically-distinct ternary encounter complex and thus that auxin perception is not limited to sequential, independent binding of auxin and then Aux/IAA to TIR1.

plant biology↗