The chloroplast has a central position in oxygenic photosynthesis and primary metabolism. In addition to these functions, the chloroplast has recently emerged as a pivotal regulator of plant responses to abiotic and biotic stress conditions. Chloroplasts have their own independent genomes and gene-expression machinery and synthesize phytohormones and a diverse range of secondary metabolites, a significant portion of which contribute the plant response to adverse conditions. Furthermore, chloroplasts communicate with the nucleus through retrograde signaling, for instance, reactive oxygen signaling. All of the above facilitate the chloroplast’s exquisite flexibility in responding to environmental stresses. In this review, we summarize recent findings on the involvement of chloroplasts in plant regulatory responses to various abiotic and biotic stresses including heat, chilling, salinity, drought, high light environmental stress conditions, and pathogen invasions. This review will enrich the better understanding of interactions between chloroplast and environmental stresses, and will lay the foundation for genetically enhancing plant-stress acclimatization.

Verticillium wilt is caused by the soil‐borne vascular pathogen Verticillium dahliae, and affects a wide range of economically important crops, including upland cotton (Gossypium hirsutum). Previous studies showed that expression levels of BIN2 were significantly down‐regulated during infestation with V. dahliae. However, the underlying molecular mechanism of BIN2 in plant regulation against V. dahliae remains enigmatic. Here, we characterized a protein kinase GhBIN2 from Gossypium hirsutum, and identified GhBIN2 as a negative regulator of resistance to V. dahliae. The Verticillium wilt resistance of Arabidopsis and cotton were significantly enhanced when BIN2 was knocked down. Constitutive expression of BIN2 attenuated plant resistance to V. dahliae. We found that BIN2 regulated plant endogenous JA content and influenced the expression of JA‐responsive marker genes. Further analysis revealed that BIN2 interacted with and phosphorylated JAZ family proteins, key repressors of the JA signalling pathway in both Arabidopsis and cotton. Spectrometric analysis and site‐directed mutagenesis showed that BIN2 phosphorylated AtJAZ1 at T196, resulting in the degradation of JAZ proteins. Collectively, these results show that BIN2 interacts with JAZ proteins and plays a negative role in plant resistance to V. dahliae. Thus, BIN2 may be a potential target gene for genetic engineering against Verticillium wilt in crops.

Plants, as sessile organisms, uptake nutrients from the soil. Throughout their whole life cycle, they confront various external biotic and abiotic threats, encompassing harmful element toxicity, pathogen infection, and herbivore attack, posing risks to plant growth and production. Plants have evolved multifaceted mechanisms to cope with exogenous stress. The element defense hypothesis (EDH) theory elucidates that plants employ elements within their tissues to withstand various natural enemies. Notably, essential and non-essential trace metals and metalloids have been identified as active participants in plant defense mechanisms, especially in nanoparticle form. In this review, we compiled and synthetized recent advancements and robust evidence regarding the involvement of trace metals and metalloids in plant element defense against external stresses that include biotic stressors (such as drought, salinity, and heavy metal toxicity) and abiotic environmental stressors (such as pathogen invasion and herbivore attack). We discuss the mechanisms underlying the metals and metalloids involved in plant defense enhancement from physiological, biochemical, and molecular perspectives. By consolidating this information, this review enhances our understanding of how metals and metalloids contribute to plant element defense. Drawing on the current advances in plant elemental defense, we propose an application prospect of metals and metalloids in agricultural products to solve current issues, including soil pollution and production, for the sustainable development of agriculture. Although the studies focused on plant elemental defense have advanced, the precise mechanism under the plant defense response still needs further investigation.

Melatonin functions as a plant hormone/regulator in the regulation of growth and development. However, the underlying mechanisms are still unclear. In this study, we found that a high dose of melatonin inhibited hypocotyl elongation in a dose-dependent manner in Arabidopsis. An expression profile analysis showed that hypocotyl growth inhibition by melatonin was involved in reprograming the expression of cell elongation genes and brassinosteroid (BRs) biosynthetic genes. Furthermore, similar to BR biosynthetic inhibitor brassinazole (BRZ), a high concentration of melatonin upregulated BR-biosynthetic genes and downregulated BR-induced genes involved in cell elongation, while melatonin was inefficient in brassinazole-resistant mutants like the bzr1-1D and bes1-D in hypocotyl inhibition. The comparative expression profile analysis showed an opposite expression mode in the co-regulated genes between melatonin and BZR1 or melatonin and brassinolide (BL). Additionally, exogenous BL rescued the repressive phenotype of BR biosynthesis-deficient mutant like det2-1 even in the presence of high-dose melatonin, but not BR receptor mutant bri1-5 or signal transduction mutant bin2-1. A biochemical analysis further confirmed that melatonin reduced endogenous BR levels in a dose-dependent manner in Arabidopsis. Taken together, these results indicate that melatonin inhibits BR biosynthesis but does not block BR signaling in the inhibition of hypocotyl elongation and extends insights on the role of melatonin in cross-talking with plant hormone signaling.

The target of rapamycin (TOR) protein kinase is an atypical Ser/Thr protein kinase and evolutionally conserved among yeasts, plants, and mammals. TOR has been established as a central hub for integrating nutrient, energy, hormone, and environmental signals in all the eukaryotes. Despite the conserved functions across eukaryotes, recent research has shed light on the multifaceted roles of TOR signaling in plant-specific functional and mechanistic features. One of the most specific features is the involvement of TOR in plant photosynthesis. The recent development of tools for the functional analysis of plant TOR has helped to uncover the involvement of TOR signaling in several steps preceding photoautotrophy and maintenance of photosynthesis. Here, we present recent novel findings relating to TOR signaling and its roles in regulating plant photosynthesis, including carbon nutrient sense, light absorptions, and leaf and chloroplast development. We also provide some gaps in our understanding of TOR function in photosynthesis that need to be addressed in the future.

Plant diseases caused by fungal phytopathogens have led to significant economic losses in agriculture worldwide. The management of fungal diseases is mainly dependent on the application of fungicides, which are not suitable for sustainable agriculture, human health, and environmental safety. Thus, it is necessary to develop novel targets and green strategies to mitigate the losses caused by these pathogens. The target of rapamycin (TOR) complexes and key components of the TOR signalling pathway are evolutionally conserved in pathogens and closely related to the vegetative growth and pathogenicity. As indicated in recent systems, chemical, genetic, and genomic studies on the TOR signalling pathway, phytopathogens with TOR dysfunctions show severe growth defects and nonpathogenicity, which makes the TOR signalling pathway to be developed into an ideal candidate target for controlling plant disease. In this review, we comprehensively discuss the current knowledge on components of the TOR signalling pathway in microorganisms and the diverse roles of various plant TOR in response to plant pathogens. Furthermore, we analyse a range of disease management strategies that rely on the TOR signalling pathway, including genetic modification technologies and chemical controls. In the future, disease control strategies based on the TOR signalling network are expected to become a highly effective weapon for crop protection.