Heat Stress Targeting Individual Organs Reveals the Central Role of Roots and Crowns in Rice Stress Responses

The role of cis-zeatin in enhancing high-temperature resistance and fucoxanthin biosynthesis in Phaeodactylum tricornutum

Phaeodactylum tricornutum a prominent source of industrial fucoxanthin production, faces challenges in its application due to its tolerance to high-temperature environments. This study investigates the physiological responses of P. tricornutum to high-temperature stress and its impact on fucoxanthin content, with a specific focus on the role of cis-zeatin. The results reveal that high-temperature stress inhibits P. tricornutum's growth and photosynthetic activity, leading to a decrease in fucoxanthin content. Transcriptome analysis shows that high temperature suppresses the expression of genes related to photosynthesis (e.g., psbO, psbQ, and OEC) and fucoxanthin biosynthesis (e.g., PYS, PDS1, and PSD2), underscoring the negative effects of high temperature on P. tricornutum. Interestingly, genes associated with cis-zeatin biosynthesis and cytokinesis signaling pathways exhibited increased expression under high-temperature conditions, indicating a potential role of cis-zeatin signaling in response to elevated temperatures. Content measurements confirm that high temperature enhances cis-zeatin content. Furthermore, the exogenous addition of cytokinesis mimetics or inhibitors significantly affected P. tricornutum's high-temperature resistance. Overexpression of the cis-zeatin biosynthetic enzyme gene tRNA DMATase enhanced P. tricornutum's resistance to high-temperature stress, while genetic knockout of tRNA DMATase reduced its resistance to high temperatures. Therefore, this research not only uncovers a novel mechanism for high-temperature resistance in P. tricornutum but also offers a possible alga species that can withstand high temperatures for the industrial production of fucoxanthin, offering valuable insights for practical utilization.IMPORTANCEThis study delves into Phaeodactylum tricornutum's response to high-temperature stress, specifically focusing on cis-zeatin. We uncover inhibited growth, reduced fucoxanthin, and significant cis-zeatin-related gene expression under high temperatures, highlighting potential signaling mechanisms. Crucially, genetic engineering and exogenous addition experiments confirm that the change in cis-zeatin levels could influence P. tricornutum's resistance to high-temperature stress. This breakthrough deepens our understanding of microalgae adaptation to high temperatures and offers an innovative angle for industrial fucoxanthin production. This research is a pivotal step toward developing heat-resistant microalgae for industrial use.

The Germin-like protein gene OsGER4 is involved in heat stress response in rice root development

Rice (Oryza sativa L.) is one of the most important dietary carbohydrate sources for half of the world's population. However, it is not well adapted to environmental stress conditions, necessitating to create new and improved varieties to help ensure sufficient rice production in the face of rising populations and shrinking arable land. Recently, the development of the CRISPR/Cas9 gene editing system has allowed researchers to study functional genomics and engineer new rice varieties with great efficiency compared to conventional methods. In this study, we investigate the involvement of OsGER4, a germin-like protein identified by a genome-wide association study that is associated with rice root development under a stress hormone jasmonic acids treatment. Analysis of the OsGER4 promoter region revealed a series of regulatory elements that connect this gene to ABA signaling and water stress response. Under heat stress, osger4 mutant lines produce a significantly lower crown root than wild-type Kitaake rice. The loss of OsGER4 also led to the reduction of lateral root development. Using the GUS promoter line, OsGER4 expression was detected in the epidermis of the crown root primordial, in the stele of the crown root, and subsequently in the primordial of the lateral root. Taken together, these results illustrated the involvement of OsGER4 in root development under heat stress by regulating auxin transport through plasmodesmata, under control by both ABA and auxin signaling.

Cytokinins act synergistically with heat acclimation to enhance rice thermotolerance affecting hormonal dynamics, gene expression and volatile emission

Heat stress is a frequent environmental constraint. Phytohormones can significantly affect plant thermotolerance. This study compares the effects of exogenous cytokinin meta-topolin-9-(tetrahydropyran-2-yl)purine (mT9THP) on rice (Oryza sativa) under control conditions, after acclimation by moderate temperature (A; 37 °C, 2h), heat stress (HS; 45 °C, 6h) and their combination (AHS). mT9THP is a stable cytokinin derivative that releases active meta-topolin gradually, preventing the rapid deactivation reported after exogenous cytokinin application. Under control conditions, mT9THP negatively affected jasmonic acid in leaves and abscisic and salicylic acids in crowns (meristematic tissue crucial for tillering). Exogenous cytokinin stimulated the emission of volatile organic compounds (VOC), especially 2,3-butanediol. Acclimation upregulated trans-zeatin, expression of stress- and hormone-related genes, and VOC emission. The combination of acclimation and mT9THP promoted the expression of stress markers and antioxidant enzymes and moderately increased VOC emission, including 2-ethylhexyl salicylate or furanones. AHS and HS responses shared some common features, namely, increase of ethylene precursor aminocyclopropane-1-carboxylic acid (ACC), cis-zeatin and cytokinin methylthio derivatives, as well as the expression of heat shock proteins, alternative oxidases, and superoxide dismutases. AHS specifically induced jasmonic acid and auxin indole-3-acetic acid levels, diacylglycerolipids with fewer double bonds, and VOC emissions [e.g., acetamide, lipoxygenase (LOX)-derived volatiles]. Under direct HS, exogenous cytokinin mimicked some positive acclimation effects. The combination of mT9THP and AHS had the strongest thermo-protective effect, including a strong stimulation of VOC emissions (including LOX-derived ones). These results demonstrate for the first time the crucial contribution of volatiles to the beneficial effects of cytokinin and AHS on rice thermotolerance.

How rice adapts to high temperatures

High-temperature stress affects crop yields worldwide. Identifying thermotolerant crop varieties and understanding the basis for this thermotolerance would have important implications for agriculture, especially in the face of climate change. Rice (Oryza sativa) varieties have evolved protective strategies to acclimate to high temperature, with different thermotolerance levels. In this review, we examine the morphological and molecular effects of heat on rice in different growth stages and plant organs, including roots, stems, leaves and flowers. We also explore the molecular and morphological differences among thermotolerant rice lines. In addition, some strategies are proposed to screen new rice varieties for thermotolerance, which will contribute to the improvement of rice for agricultural production in the future.

Effect of ascorbate and hydrogen peroxide on hormone and metabolite levels during post-germination growth in wheat

The modulation of hormone and metabolite levels by ascorbate (ASA) and hydrogen peroxide (H₂ O₂ ) was compared during post-germination growth in shoots of wheat. Treatment with ASA resulted in a greater reduction of growth than the addition of H₂ O₂ . ASA also had a larger effect on the redox state of the shoot tissues as shown by the higher ASA and glutathione (GSH) levels, lower glutathione disulfide (GSSG) content and GSSG/GSH ratio compared to the H₂ O₂ treatment. Apart from common responses (i.e., increase of cis-zeatin and its O-glucosides), the contents of several compounds related to cytokinin (CK) and abscisic acid (ABA) metabolism were greater after ASA application. These differences in the redox state and hormone metabolism following the two treatments may be responsible for their distinct influence on various metabolic pathways. Namely, the glycolysis and citrate cycle were inhibited by ASA and they were not affected by H₂ O₂ , while the amino acid metabolism was induced by ASA and repressed by H₂ O₂ based on the changes in the level of the related carbohydrates, organic and amino acids. The first two pathways produce reducing power, while the last one needs it; therefore ASA, as a reductant may suppress and induce them, respectively. H₂ O₂ as an oxidant had different effect, namely it did not alter glycolysis and citrate cycle, and inhibited the formation of amino acids.

Positively Charged Microplastics Induce Strong Lettuce Stress Responses from Physiological, Transcriptomic, and Metabolomic Perspectives

Microplastics (MPs) can enter plants through the foliar pathway and are potential hazards to ecosystems and human health. However, studies related to the molecular mechanisms underlying the impact of foliar exposure to differently charged MPs to leafy vegetables are limited. Because the surfaces of MPs in the environment are often charged, we explored the uptake pathways, accumulation concentration of MPs, physiological responses, and molecular mechanisms of lettuce foliarly exposed to MPs carrying positive (MP+) and negative charges (MP-). MPs largely accumulated in the lettuce leaves, and stomatal uptake and cuticle entry could be the main pathways for MPs to get inside lettuce leaves. More MP+ entered lettuce leaves and induced physiological, transcriptomic, and metabolomic changes, including a decrease in biomass and photosynthetic pigments, an increase in reactive oxygen species and antioxidant activities, a differential expression of genes, and a change of metabolite profiles. In particular, MP+ caused the upregulation of circadian rhythm-related genes, and this may play a major role in the greater physiological toxicity of MP+ to lettuce, compared to MP-. These findings provide direct evidence that MPs can enter plant leaves following foliar exposure and a molecular-scale perspective on the response of leafy vegetables to differently charged MPs.

Cytokinins: Wide-Spread Signaling Hormones from Plants to Humans with High Medical Potential

Nature is a rich source of biologically active novel compounds. Sixty years ago, the plant hormones cytokinins were first discovered. These play a major role in cell division and cell differentiation. They affect organogenesis in plant tissue cultures and contribute to many other physiological and developmental processes in plants. Consequently, the effect of cytokinins on mammalian cells has caught the attention of researchers. Many reports on the contribution and potential of cytokinins in the therapy of different human diseases and pathophysiological conditions have been published and are reviewed here. We compare cytokinin effects and pathways in plants and mammalian systems and highlight the most important biological activities. We present the strong profile of the biological actions of cytokinins and their possible therapeutic applications.