Search

The chloroplast is a critical battleground in the arms race between plants and pathogens. Among microbe-secreted mycotoxins, tenuazonic acid (TeA), produced by the genus Alternariaand other phytopathogenic fungi, inhibits photosynthesis, leading to a burst of photosynthetic singlet oxygen (1O2) that is implicated in damage and chloroplast-to-nucleus retrograde signaling. Despite the significant crop damage caused by Alternariapathogens, our understanding of the molecular mechanism by which TeA promotes pathogenicity and cognate plant defense responses remains fragmentary. We now reveal that A. alternatainduces necrotrophic foliar lesions by harnessing EXECUTER1 (EX1)/EX2-mediated chloroplast-to-nucleus retrograde signaling activated by TeA toxin–derived photosynthetic 1O2in Arabidopsis thaliana. Mutation of the 1O2-sensitive EX1-W643 residue or complete deletion of the EX1 singlet oxygen sensor domain compromises expression of 1O2-responsive nuclear genes and foliar lesions. We also found that TeA toxin rapidly induces nuclear genes implicated in jasmonic acid (JA) synthesis and signaling, and EX1-mediated retrograde signaling appears to be critical for establishing a signaling cascade from 1O2to JA. The present study sheds new light on the foliar pathogenicity of A. alternata, during which EX1-dependent 1O2signaling induces JA-dependent foliar cell death.

A simple relay selection scheme is proposed for analog network coding using differential modulation (ANC-DM). We propose a relay selection scheme based solely on the received signal power in which their own information is canceled out at each source node. The proposed power-based relay selection scheme is further applied to analog network coding using double-differential modulation (ANC-DDM), which is suitable for channels with carrier offset. Simulation results show that our proposed simple power-based criterion for relay selection in ANC-DM system has little loss compared to the optimal relay selection scheme using ideal BER.

Clathrin-mediated vesicular formation and trafficking are responsible for molecular cargo transport and signal transduction among organelles. Our previous study showed that CHLOROPLAST VESICULATION(CV)-containing vesicles (CVVs) were generated from chloroplasts for chloroplast degradation under abiotic stress. Here, we show that CV interacts with the clathrin heavy chain (CHC) and induces vesicle budding towards the cytosol from the chloroplast inner envelope membrane. In the defective mutants of CHC2and the dynamin-encoding DRP1A, CVV budding and releasing from chloroplast is impeded. Genetically, the mutations of CHC2inhibit CV-induced chloroplast degradation and hypersensitivity to water stress. Moreover, CV-CHC2 interaction is impaired by the oxidized GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE (GAPC). GAPC1overexpression suppresses CV-mediated chloroplast degradation and hypersensitivity to water stress, while CVsilencing alleviates the hypersensitivity of gapc1gapc2plant to water stress. Together, our work reveals a previously-unknown pathway of clathrin-assisted CVV budding outwards from chloroplast, which is involved in chloroplast degradation and stress response.

Chloroplasts overproduce reactive oxygen species (ROS) under unfavorable environmental conditions, and these ROS are implicated in both signaling and oxidative damage. There is mounting evidence for their roles in translating environmental fluctuations into distinct physiological responses, but their targets, signaling cascades, and mutualism and antagonism with other stress signaling cascades and within ROS signaling remain poorly understood. Great efforts made in recent years have shed new light on chloroplast ROS-directed plant stress responses, from ROS perception to plant responses, in conditional mutants of Arabidopsis thalianaor under various stress conditions. Some articles have also reported the mechanisms underlying the complexity of ROS signaling pathways, with an emphasis on spatiotemporal regulation. ROS and oxidative modification of affected target proteins appear to induce retrograde signaling pathways to maintain chloroplast protein quality control and signaling at a whole-cell level using stress hormones. This review focuses on these seemingly interconnected chloroplast-to-nucleus retrograde signaling pathways initiated by ROS and ROS-modified target molecules. We also discuss future directions in chloroplast stress research to pave the way for discovering new signaling molecules and identifying intersectional signaling components that interact in multiple chloroplast signaling pathways.

We present a protocol for analyzing and evaluating the relocalization of proteins from the plasma membrane to chloroplasts. Some plant membrane-bound proteins carry dual targeting signals, e.g., a membrane-anchoring N-myristoylation motif and a chloroplast transit peptide. These proteins are predominantly targeted to membranes; upon certain cues, however, they can undergo detachment from membranes and relocalization to chloroplasts. This protocol combines imaging and biochemical analyses to track in a reliable and quantitative manner the relocalization of proteins between subcellular organelles.

We have isolated a cDNA clone, OsFOR1, from the immature panicles of rice. The OsFOR1(Oryza sativa floral organ regulator 1) gene encodes a protein that contains a leucine-rich repeat (LRR) domain. This domain comprises 10 tandem repeats of a canonical 24-amino acid LRR sequence. The structure and the number of LRRs for OsFOR1 are similar to those of polygalacturonase-inhibiting proteins (PGIPs) from various other plant species. Moreover, the OsFOR1 recombinant protein, when fused to maltose-binding protein (MBP), shows PGIP activity against the Aspergillus nigerpolygalacturonase. OsFOR1is highly expressed in the calli and immature and mature panicles, while detectable at only low levels in seedling roots and mature stems. In situhybridization experiments showed the transcripts of OsFOR1are present in young spikelet primordia and in almost all of the young floral organs. Transgenic approaches were used to study in vivofunctioning. Antisense expression of OsFOR1resulted in an increase in the numbers of floral organs, including the stamen, carpel, palea/lemma, stigma, and lodicule. OsFOR1transcript was not detected in the frizzy paniclemutant, which is defective in its spikelet formation but normal in inflorescence-meristem initiation and maintenance. Therefore, we suggest that OsFOR1plays a role in the formation and/or maintenance of floral organ primordia.

ABSTRACTSinglet oxygen (1O2) is a potent oxidizing agent, principally generated by photosystem II (PSII) as a byproduct of photosynthesis. Hence, 1O2damages PSII, especially the PSII reaction center (RC) proteins, promoting a process called PSII repair cycle. The hetero-hexameric FtsH protease, located in the thylakoid membrane, is essential in degrading these damaged PSII RC proteins, which defines the first step of the PSII repair. The loss of the central subunit of the FtsH protease, FtsH2 (VAR2), weakens the PSII repair, thereby impairing PSII proteostasis. A recent study demonstrated that the impaired proteostasis (or accumulation of damaged proteins) in the chloroplasts of the var2mutant induces an unfolded/misfolded protein response (UPR)-like response, more appropriately referred to as a damaged protein response (DPR), as evident in the accumulation of proteins related to the protein quality control (PQC). Comparison of data from chloroplast proteomics data with RNA sequencing in the context of the UPR-like response suggests a plausible activation of retrograde signaling in the var2mutant. Either through the enhanced level of 1O2or by impairing the substrate-unfolding activity of FtsH2, the reinforced defect appears to induce stress-related genes via the stress hormone salicylic acid (SA). This finding suggests that impaired chloroplast proteostasis (specifically for PSII proteins) may activate the chloroplast-established isochorismate pathway to produce SA. If this assumption is correct, then SA serves as a retrograde signaling molecule. In this review, we will discuss the impact of chloroplast proteostasis on chloroplasts-to-nucleus communication.