Pharmacological analysis of transmission activation of two aphid-vectored plant viruses, turnip mosaic virus and cauliflower mosaic virus

Turnip mosaic virus (TuMV, family Potyviridae) and cauliflower mosaic virus (CaMV, family Caulimoviridae) are transmitted by aphid vectors. They are the only viruses shown so far to undergo transmission activation (TA) immediately preceding plant-to-plant propagation. TA is a recently described phenomenon where viruses respond to the presence of vectors on the host by rapidly and transiently forming transmissible complexes that are efficiently acquired and transmitted. Very little is known about the mechanisms of TA and on whether such mechanisms are alike or distinct in different viral species. We use here a pharmacological approach to initiate the comparison of TA of TuMV and CaMV. Our results show that both viruses rely on calcium signaling and reactive oxygen species (ROS) for TA. However, whereas application of the thiol-reactive compound N-ethylmaleimide (NEM) inhibited, as previously shown, TuMV transmission it did not alter CaMV transmission. On the other hand, sodium azide, which boosts CaMV transmission, strongly inhibited TuMV transmission. Finally, wounding stress inhibited CaMV transmission and increased TuMV transmission. Taken together, the results suggest that transmission activation of TuMV and CaMV depends on initial calcium and ROS signaling that are generated during the plant's immediate responses to aphid manifestation. Interestingly, downstream events in TA of each virus appear to diverge, as shown by the differential effects of NEM, azide and wounding on TuMV and CaMV transmission, suggesting that these two viruses have evolved analogous TA mechanisms

Recycling, clustering, and endocytosis jointly maintain PIN auxin carrier polarity at the plasma membrane

A combination of super-resolution microscopy in live cells and computational modeling provides new insights into the dynamic and interwoven mechanism that maintains the polar distribution of an important plant cargo

Protein kinase SnRK2. 4 is a key regulator of aquaporins and root hydraulics in Arabidopsis

Soil water uptake by roots is a key component of plant water homeostasis contributing to plant growth and survival under ever-changing environmental conditions. The water transport capacity of roots (root hydraulic conductivity; Lpr ) is mostly contributed by finely regulated Plasma membrane Intrinsic Protein (PIP) aquaporins. In this study, we used natural variation of Arabidopsis for the identification of quantitative trait loci (QTLs) contributing to Lpr . Using recombinant lines from a biparental cross (Cvi-0 x Col-0), we show that the gene encoding class 2 Sucrose-Non-Fermenting Protein kinase 2.4 (SnRK2.4) in Col-0 contributes to >30% of Lpr by enhancing aquaporin-dependent water transport. At variance with the inactive and possibly unstable Cvi-0 SnRK2.4 form, the Col-0 form interacts with and phosphorylates the prototypal PIP2;1 aquaporin at Ser121 and stimulates its water transport activity upon coexpression in Xenopus oocytes and yeast cells. Activation of PIP2;1 by Col-0 SnRK2.4 in yeast also requires its protein kinase activity and can be counteracted by clade A Protein Phosphatases 2C. SnRK2.4 shows all hallmarks to be part of core abscisic acid (ABA) signaling modules. Yet, long-term (>3 h) inhibition of Lpr by ABA possibly involves a SnRK2.4-independent inhibition of PIP2;1. SnRK2.4 also promotes stomatal aperture and ABA-induced inhibition of primary root growth. The study identifies a key component of Lpr and sheds new light on the functional overlap and specificity of SnRK2.4 with respect to other ABA-dependent or independent SnRK2s

Etude de la transmission du CaMV (Cauliflower Mosaic Virus) à l'échelle de la cellule hôte

UMR BGPI - Equipe 2 Diplôme : Dr. d'UniversiteThe vast majority of plant viruses being transmitted from host to host by vectors, studying the process of transmission is of interest to both basic and applied research. While the molecular interactions between viruses and their vectors are the object of many studies, the participation of the host in the transmission mechanism seems to have been neglected. Thus, the host cell is often considered as a mere “sac” from which the viruses are accidentally acquired by the vector. However, the CaMV forms in infected host cells a structure specialised and mandatory for transmission, the electron-lucent inclusion body (EL). Consequently, the issues addressed in this thesis were (i) to determine how ELs form in infected host cells, and (ii) to determine how the CaMV is acquired by its vector. To address the first question, we searched to identify cellular partners involved in EL formation. Our results show that microtubules are required for their formation and suggest that the kinesin TBK5 transports the CaMV proteins via microtubules from their site of synthesis to emerging ELs. Concerning the mechanisms of CaMV acquisition by its aphid vector, we show that the wounding caused by the intracellular puncture of the aphid provokes a cellular stimulus triggering a calcium-mediated signaling cascade. After this stimulus, an important influx of tubulin into the EL. This process might “activate” the EL, since it is accompanied by a highly significant increase of the transmission rate of CaMV by its vector. Taken together, our results indicate that the process of transmission of CaMV is finely tuned on the level of each infected cell, which not only participates in EL formation but also in its “activation”.La grande majorité des phytovirus étant transmis d’hôte en hôte par vecteur, l’étude des processus de transmission présente un intérêt tant fondamental qu’appliqué. Alors que les interactions moléculaires entre le virus et son vecteur font l’objet de nombreuses études, les mécanismes cellulaires impliqués dans la transmission ont été peu étudiés. La cellule est ainsi souvent considérée comme un sac dans lequel les virus sont prélevés passivement par le vecteur. Le CaMV développe pourtant dans les cellules hôtes un « corps d’inclusion clair », structure spécialisée et indispensable à la transmission. De ce fait, le présent travail met la cellule hôte au centre des recherches. Tout d’abord, nous avons cherché à identifier les partenaires cellulaires permettant la formation des corps clairs. Les résultats montrent que les microtubules sont indispensables à leur formation et suggèrent que la kinésine TBK5 transporte des protéines viral sur les microtubules, de leur site de synthèse vers les corps clairs émergeant. Nous nous sommes, ensuite, focalisé sur les évènements cellulaires se produisant lors de l’acquisition du virus par le puceron. La blessure provoquée par la piqûre intracellulaire du puceron, provoque un stimulus déclenchant une cascade de signalisation via la voie calcique. Après cette blessure, la tubuline afflue massivement dans les corps clairs. Ce processus semble alors les « activer » car il augmente très significativement la transmission des virus par leurs vecteurs. Nos résultats indiquent que le processus de transmission du CaMV par vecteur est finement régulé au sein de chaque cellule infectée, celle-ci participant non seulement à la synthèse du corps clair mais également à son « activation »

Cauliflower mosaic virus, transmission and tubulin

National audienc

Protein diffusion in plant cell plasma membranes: the cell-wall corral.

International audienceStudying protein diffusion informs us about how proteins interact with their environment. Work on protein diffusion over the last several decades has illustrated the complex nature of biological lipid bilayers. The plasma membrane contains an array of membrane-spanning proteins or proteins with peripheral membrane associations. Maintenance of plasma membrane microstructure can be via physical features that provide intrinsic ordering such as lipid microdomains, or from membrane-associated structures such as the cytoskeleton. Recent evidence indicates, that in the case of plant cells, the cell wall seems to be a major player in maintaining plasma membrane microstructure. This interconnection / interaction between cell-wall and plasma membrane proteins most likely plays an important role in signal transduction, cell growth, and cell physiological responses to the environment

Membrane nanodomains and transport functions in plant

International audienceAbstract Far from a homogeneous environment, biological membranes are highly structured with lipids and proteins segregating in domains of different sizes and dwell times. In addition, membranes are highly dynamics especially in response to environmental stimuli. Understanding the impact of the nanoscale organization of membranes on cellular functions is an outstanding question. Plant channels and transporters are tightly regulated to ensure proper cell nutrition and signaling. Increasing evidence indicates that channel and transporter nano-organization within membranes plays an important role in these regulation mechanisms. Here, we review recent advances in the field of ion, water, but also hormone transport in plants, focusing on protein organization within plasma membrane nanodomains and its cellular and physiological impacts

Rôle de la tubuline dans la morphogenèse spécifique de deux types de corps d'inclusion viraux intracellulaires provoqués par l'infection avec le Cauliflower mosaic virus

National audienc