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Abstract Phosphatidylinositol 4-kinases (PI4Ks) are the first enzymes that commit phosphatidylinositol into the phosphoinositide pathway. Here, we show that Arabidopsis thaliana seedlings deficient in PI4Kβ1 and β2 have several developmental defects including shorter roots and unfinished cytokinesis. The pi4kβ1β2 double mutant was insensitive to exogenous auxin concerning inhibition of root length and cell elongation; it also responded more slowly to gravistimulation. The pi4kß1ß2 root transcriptome displayed some similarities to a wild type plant response to auxin. Yet, not all the genes displayed such a constitutive auxin-like response. Besides, most assessed genes did not respond to exogenous auxin. This is consistent with data with the transcriptional reporter DR5-GUS. The content of bioactive auxin in the pi4kß1ß2 roots was similar to that in wild-type ones. Yet, an enhanced auxin-conjugating activity was detected and the auxin level reporter DII-VENUS did not respond to exogenous auxin in pi4kß1ß2 mutant. The mutant exhibited altered subcellular trafficking behavior including the trapping of PIN-FORMED 2 protein in rapidly moving vesicles. Bigger and less fragmented vacuoles were observed in pi4kß1ß2 roots when compared to the wild type. Furthermore, the actin filament web of the pi4kß1ß2 double mutant was less dense than in wild-type seedling roots, and less prone to rebuilding after treatment with latrunculin B. A mechanistic model is proposed in which an altered PI4K activity leads to actin filament disorganization, changes in vesicle trafficking, and altered auxin homeostasis and response resulting in a pleiotropic root phenotypes.

Phytopathogenic bacteria are one of the most significant causes of crop yield losses. Until now, the direct treatment of bacterioses was limited to the application of antibacterial compounds or resistance inducers. This is about to change due to the revolutionary discovery of phages. Indeed, bacteriophages look very promising as therapy agents: cheap, self-amplifying, self-eliminating, and safe for the host organism. However, phage therapy of plant diseases remains a "direction with high potential", which, so far, has very few successful implication cases. Here, we discuss recent advances in phage research, focusing on the challenges associated with the evaluation of phage biological activity, under both laboratory and environmental conditions.

Aphids, the phloem sap feeders, probe into leaf tissues and activate a complex network of plant defense responses. Phytohormonal signaling plays a major role in this network; however, the dynamics of the signal spreading is yet to be clarified. Despite the growing knowledge about transcriptomic changes upon infestation, results often differ due to sampling, varying strongly between the tissues collected at the single feeding site, individual leaves, pooled infested leaves, or whole plant rosettes. This study focuses on activation of salicylic acid (SA) and jasmonic acid (JA) signals in Arabidopsis leaves during infestation by cabbage aphid (Brevicoryne brassicae) in high spatio-temporal resolution. We used genetically encoded fluorescent biosensors, histochemistry, and quantitative reverse transcription-PCR to precisely map activation of distinct branches of phytohormonal signaling. We found a rapid induction of SA and JA signaling markers in cells surrounding stylet puncture, colocalizing with callose deposition. For both PR1 and JAZ10, we detected activation at 24 h postinfestation (hpi), increasing and spreading along the veins until 72 hpi and, to a lesser extent, within the epidermal pavement cells. The SA signaling wave appeared in parallel with JA-associated signaling and continued to increase in time. Our results first show a local activation of SA- and JA-related responses after stylet penetration of Arabidopsis leaves and bring a detailed insight into the spatio-temporal complexity of plant defense activation during specialist aphid attack.[Graphic: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Pseudomonas syringae is a bacterial pathogen that causes yield losses in various economically important plant species. At the same time, P. syringae pv. tomato (Pst) is one of the best-studied bacterial phytopathogens and a popular model organism. In this study, we report on the isolation of two phages from the market-bought pepper fruit showing symptoms of bacterial speck. These Pseudomonas phages were named Eir4 and Eisa9 and characterized using traditional microbiological methods and whole-genome sequencing followed by various bioinformatics approaches. Both of the isolated phages were capable only of the lytic life cycle and were efficient against several pathovars from Pseudomonas and Xanthomonas genera. With the combination of transmission electron microscopy (TEM) virion morphology inspection and comparative genomics analyses, both of the phages were classified as members of the Autographiviridae family with different degrees of novelty within the known phage diversity. Eir4, but not Eisa9, phage application significantly decreased the propagation of Pst in the leaf tissues of Arabidopsis thaliana plants. The biological properties of Eir4 phage allow us to propose it as a potential biocontrol agent for use in the prevention of Pst-associated bacterioses and also as a model organism for the future research of mechanisms of phage–host interactions in different plant systems.

Brassinosteroids (BRs) are plant hormones of steroid nature, regulating various developmental and adaptive processes. The perception, transport, and signaling of BRs are actively studied nowadays via a wide range of biochemical and genetic tools. However, most of the knowledge about BRs intracellular localization and turnover relies on the visualization of the receptors or cellular compartments using dyes or fluorescent protein fusions. We have previously synthesized a conjugate of epibrassinolide with green fluorescent dye BODIPY (eBL-BODIPY). Here we present a detailed assessment of the compound bioactivity and its suitability as probe for in vivo visualization of BRs. We show that eBL-BODIPY rapidly penetrates epidermal cells of Arabidopsis thaliana roots and after long exposure causes physiological and transcriptomic responses similar to the natural hormone.