Biomedical subjects

Richard Napier

Publications and source records attributed to Richard Napier.

4 recordsLinked to original sources

PubMed2025

A transposable element insertion in AUX/IAA16 disrupts splicing and causes auxin resistance in Bassia scoparia.

A dicamba-resistant population of kochia (Bassia scoparia) identified in Colorado, USA in 2012 was used to generate a synthetic mapping population that segregated for dicamba resistance. Linkage mapping associating dicamba injury with genotype derived from restriction-site-associated DNA sequencing identified a single locus in the kochia genome associated with resistance on chromosome 4. A mutant version of Auxin/Indole-3-Acetic Acid 16 (AUX/IAA16; a gene previously implicated in dicamba resistance in kochia) was found near the middle of this locus in resistant plants. Long-read sequencing of dicamba-resistant plants identified a recently inserted long-terminal repeat (LTR) retrotransposon TRIM element near the beginning of the second exon of AUX/IAA16, leading to disruption of normal splicing and a mutated degron domain. Stable transgenic lines of Arabidopsis thaliana ectopically expressing the mutant and wild-type alleles of AUX/IAA16 were developed. Arabidopsis thaliana plants expressing the mutant AUX/IAA16 allele grew shorter roots on control media. However, transgenic root growth was less inhibited on media containing either dicamba (5 μM) or IAA (0.5 μM) when compared with non-transgenic plants or those expressing the wild-type allele of AUX/IAA16. In vitro assays indicate reduced binding affinity and more rapid dissociation of the mutant AUX/IAA16 with TIR1 in the presence of several auxins, and protein modeling suggests the substitution of the glycine residue in the degron domain of AUX/IAA16 is especially important for resistance. A fitness cost associated with the mutant allele of AUX/IAA16 has implications for resistance evolution and management of kochia populations with this resistance mechanism.

Indoleacetic Acids↗

PubMed2004

Structure-function analysis of the presumptive Arabidopsis auxin permease AUX1.

We have investigated the subcellular localization, the domain topology, and the amino acid residues that are critical for the function of the presumptive Arabidopsis thaliana auxin influx carrier AUX1. Biochemical fractionation experiments and confocal studies using an N-terminal yellow fluorescent protein (YFP) fusion observed that AUX1 colocalized with plasma membrane (PM) markers. Because of its PM localization, we were able to take advantage of the steep pH gradient that exists across the plant cell PM to investigate AUX1 topology using YFP as a pH-sensitive probe. The YFP-coding sequence was inserted in selected AUX1 hydrophilic loops to orient surface domains on either apoplastic or cytoplasmic faces of the PM based on the absence or presence of YFP fluorescence, respectively. We were able to demonstrate in conjunction with helix prediction programs that AUX1 represents a polytopic membrane protein composed of 11 transmembrane spanning domains. In parallel, a large aux1 allelic series containing null, partial-loss-of-function, and conditional mutations was characterized to identify the functionally important domains and amino acid residues within the AUX1 polypeptide. Whereas almost all partial-loss-of-function and null alleles cluster in the core permease region, the sole conditional allele aux1-7 modifies the function of the external C-terminal domain.

Alleles↗

PubMed2004

Plant hormone binding sites.

AIMS: Receptors for plant hormones are becoming identified with increasing rapidity, although a frustrating number remain unknown. There have also been many more hormone-binding proteins described than receptors. This Botanical Briefing summarizes what has been discovered about hormone binding sites, their discovery and descriptions, and will not dwell on receptor functions or activities except where these are relevant to understand binding. SCOPE: Of those receptors identified, each falls into recognized protein superfamilies. Ethylene and cytokinin receptors have intracellular histidine kinase phosphorelay domains, but the ligand-binding sites are distinct, one being buried within membrane-spanning helices, the other in an extracellular loop domain. Brassinosteroid and phytosulfokine receptors are members of the leucine-rich repeat receptor-like protein superfamily and for these the ligand binding sites are likely to be in one of the loops of the extracellular leucine-rich domain. For auxin, the auxin-binding protein ABP1 is a member of the cupin superfamily and the binding site is in a hydrophobic pocket at the head of which is a zinc ion to coordinate the acid group of the ligand. Receptors for other plant hormones have still to be identified. CONCLUSIONS: Plant hormone receptors have been identified through the application of many different techniques; no one technique is likely to prove more successful than any other for discovering new receptors. At present there is structural detail only for auxin binding, although a good model exists for the amino acid residues needed for Cu(I) and ethylene binding. In this respect plant biology is very poor and effort needs to be put into receptor discovery and molecular characterization. The information accumulated by such work will undoubtedly indicate many new ways in which plant growth and development can be manipulated, but knowledge-led design of new ligands or of altered sensitivities is still some way off.

Abscisic Acid↗

PubMed2003

Growth of plant culture.

A series of articles by Nick Battey published throughout 2003 has been challenging plant scientists to embrace plant culture. Fine art, literature, mythology, plant lore, religion, philosophy and plant science all contribute to plant culture and Battey believes that it is up to us, the scientists, to stimulate greater appreciation of our work by striving for a richer culture.

Art↗