Interaction specificity of Arabidopsis 14-3-3 proteins with phototropin receptor kinases

Phototropin receptor kinases play an important roles in optimising plant growth in response to blue light. Much is known regarding their photochemical reactivity, yet little progress has been made to identify downstream signalling components. Here, we isolated several interacting proteins for Arabidopsis phototropin 1 (phot1) by yeast two-hybrid screening. These include members of the NPH3/RPT2 (NRL) protein family, proteins associated with vesicle trafficking, and the 14-3-3 lambda (?) isoform from Arabidopsis . 14-3-3? and phot1 were found to colocalise and interact in vivo. Moreover, 14-3-3 binding to phot1 was limited to non-epsilon 14-3-3 isoforms and was dependent on key sites of receptor autophosphorylation. No 14-3-3 binding was detected for Arabidopsis phot2, suggesting that 14-3-3 proteins represent specific mode of phot1 signalling

phot1 inhibition of ABCB19 primes lateral auxin fluxes in the shoot apex required for phototropism

It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots. Here, we establish a system in Arabidopsis thaliana to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis. We show that auxin redistribution to the epidermal sites of action occurs at and above the hypocotyl apex, not at the elongation zone. Within this region, we identify the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as a substrate target for the photoreceptor kinase PHOTOTROPIN 1 (phot1). Heterologous expression and physiological analyses indicate that phosphorylation of ABCB19 by phot1 inhibits its efflux activity, thereby increasing auxin levels in and above the hypocotyl apex to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN-FORMED 3 (PIN3). Together, these results provide new insights into the roles of ABCB19 and PIN3 in establishing phototropic curvatures and demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperm

REPRESSOR OF ULTRAVIOLET-B PHOTOMORPHOGENESIS function allows efficient phototropin mediated ultraviolet-B phototropism in etiolated seedlings.

Ultraviolet B (UV-B) light is a part of the solar radiation which has significant effects on plant morphology, even at low doses. In Arabidopsis, many of these morphological changes have been attributed to a specific UV-B receptor, UV resistance locus 8 (UVR8). Recent findings showed that next to phototropin regulated phototropism, UVR8 mediated signaling is able of inducing directional bending towards UV-B light in etiolated seedlings of Arabidopsis, in a phototropin independent manner. In this study, kinetic analysis of phototropic bending was used to evaluate the relative contribution of each of these pathways in UV-B mediated phototropism. Diminishing UV-B light intensity favors the importance of phototropins. Molecular and genetic analyses suggest that UV-B is capable of inducing phototropin signaling relying on phototropin kinase activity and regulation of NPH3. Moreover, enhanced UVR8 responses in the UV-B hypersensitive rup1rup2 mutants interferes with the fast phototropin mediated phototropism. Together the data suggest that phototropins are the most important receptors for UV-B induced phototropism in etiolated seedlings, and a RUP mediated negative feedback pathway prevents UVR8 signaling to interfere with the phototropin dependent response

Phototropins maintain robust circadian oscillation of PSII operating efficiency under blue light

The circadian system allows plants to coordinate metabolic and physiological functions with predictable environmental variables such as dusk and dawn. This endogenous oscillator is comprised of biochemical and transcriptional rhythms that are synchronized with a plant's surroundings via environmental signals, including light and temperature. We have used chlorophyll fluorescence techniques to describe circadian rhythms of PSII operating efficiency (Fq′/Fm′) in the chloroplasts of Arabidopsis thaliana. These Fq′/Fm′ oscillations appear to be influenced by transcriptional feedback loops previously described in the nucleus, and are induced by rhythmic changes in photochemical quenching over circadian time. Our work reveals that a family of blue photoreceptors, phototropins, maintain robust rhythms of Fq′/Fm′ under constant blue light. As phototropins do not influence circadian gene expression in the nucleus our imaging methodology highlights differences between the modulation of circadian outputs in distinct subcellular compartments

NPH3- and PGP-like genes are exclusively expressed in the apical tip region essential for blue-light perception and lateral auxin transport in maize coleoptiles

Phototropic curvature results from differential growth on two sides of the elongating shoot, which is explained by asymmetrical indole-3-acetic acid (IAA) distribution. Using 2 cm maize coleoptile segments, 1st positive phototropic curvature was confirmed here after 8 s irradiation with unilateral blue light (0.33 μmol m−2 s−1). IAA was redistributed asymmetrically by approximately 20 min after photo-stimulation. This asymmetric distribution was initiated in the top 0–3 mm region and was then transmitted to lower regions. Application of the IAA transport inhibitor, 1-N-naphthylphthalamic acid (NPA), to the top 2 mm region completely inhibited phototropic curvature, even when auxin was simultaneously applied below the NPA-treated zone. Thus, lateral IAA movement occurred only within the top 0–3 mm region after photo-stimulation. Localized irradiation experiments indicated that the photo-stimulus was perceived in the apical 2 mm region. The results suggest that this region harbours key components responsible for photo-sensing and lateral IAA transport. In the present study, it was found that the NPH3- and PGP-like genes were exclusively expressed in the 0–2 mm region of the tip, whereas PHOT1 and ZmPIN1a, b, and c were expressed relatively evenly along the coleoptile, and ZmAUX1, ZMK1, and ZmSAURE2 were strongly expressed in the elongation zone. These results suggest that the NPH3-like and PGP-like gene products have a key role in photo-signal transduction and regulation of the direction of auxin transport after blue light perception by phot1 at the very tip region of maize coleoptiles

Discovery of nucleotide polymorphisms in the Musa gene pool by Ecotilling

Musa (banana and plantain) is an important genus for the global export market and in local markets where it provides staple food for approximately 400 million people. Hybridization and polyploidization of several (sub)species, combined with vegetative propagation and human selection have produced a complex genetic history. We describe the application of the Ecotilling method for the discovery and characterization of nucleotide polymorphisms in diploid and polyploid accessions of Musa. We discovered over 800 novel alleles in 80 accessions. Sequencing and band evaluation shows Ecotilling to be a robust and accurate platform for the discovery of polymorphisms in homologous and homeologous gene targets. In the process of validating the method, we identified two single nucleotide polymorphisms that may be deleterious for the function of a gene putatively important for phototropism. Evaluation of heterozygous polymorphism and haplotype blocks revealed a high level of nucleotide diversity in Musa accessions. We further applied a strategy for the simultaneous discovery of heterozygous and homozygous polymorphisms in diploid accessions to rapidly evaluate nucleotide diversity in accessions of the same genome type. This strategy can be used to develop hypotheses for inheritance patterns of nucleotide polymorphisms within and between genome types. We conclude that Ecotilling is suitable for diversity studies in Musa, that it can be considered for functional genomics studies and as tool in selecting germplasm for traditional and mutation breeding approaches

Equality and the Morality of Social Status

This dissertation develops an account of the concept of social status and defends an egalitarian principle concerning a distinctive kind of social status, which I call public social status. Roughly put, one’s public social status is the relative excellence that other members of society believe that one has in comparison to other members. Inequalities of public social status, I argue, amount to a profound condition of moral unfreedom for the low status. The heart of the dissertation consists of the development and defense of the principle of equal public social status. Subsequent chapters explore the relationship between that principle and other substantive normative issues in political philosophy. Topics discussed include the justification of democratic institutions, the grounds of democratic authority, and the implications of the principle of equal public social status for the organization of social cooperation and distributive justice

Justice, Reciprocity, and the Boundaries of State Authority

12 month embargo; first published online 21 March 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Adjudicating distributive disagreement

This paper examines different mechanisms for adjudicating disagreement about distributive justice. It begins with a case where individuals have deeply conflicting convictions about distributive justice and must make a social choice regarding the distribution of goods. Four mechanisms of social choice are considered: social contract formation, Borda count vote, simple plurality vote, and minimax bargaining. I develop an agent-based model which examines which mechanisms lead to the greatest degree of satisfying justice-based preferences over the course iterated social choices. Agents are ascribed two kinds of motivations: they wish to realize justice and to receive a greater package of goods. Each agent seeks to realize her ideal distribution, and the failure to do so leaves agents "disappointed," resulting in their trading off the pursuit of gains in justice in favor of gains in self-interest. Mechanisms are assessed using the metric of how many agents remain interested in justice over the course of iterated adjudication. The mechanisms are also examined under some non-ideal conditions, such as the presence of power asymmetries or strategic behavior. Several significant results are addressed: social contract formation and simple plurality voting are robust under the conditions considered, bargaining is a highly ineffective means of adjudicating distributive disagreement, and lastly allowing for concessions in justice for gains in self-interest proves to be a crucial mechanism for ensuring the stability of resolutions.12 month embargo: published online: 24 October 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Democratic Public Justification

Democratic institutions are appealing means of making publicly justified social choices. By allowing participation by all citizens, democracy can accommodate diversity among citizens, and by considering the perspectives of all, via ballots or debate, democratic results can approximate what the balance of reasons favors. I consider whether, and under what conditions, democratic institutions might reliably make publicly justified social decisions. I argue that conventional accounts of democracy, constituted by voting or deliberation, are unlikely to be effective public justification mechanisms. I conclude that the limitations of conventional mechanisms can be ameliorated through the use of lotteries instead of elections.18 month embargo; first published online 13 November 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]