Journal of Experimental Botany最新文献

Activity of the root apical meristem and hence plant growth strictly depends on glutathione homeostasis. Despite compelling evidence for this dependency based on glutathione depletion, the cause for the growth arrest had remained unclear. Meristem control may depend on either the absolute amount of glutathione or on the glutathione redox potential (EGSH). To unambiguously distinguish those two options, we characterized an allelic series of six Arabidopsis mutants affected in glutamate-cysteine ligase, which catalyses the first step for the biosynthesis of reduced glutathione (GSH). When grown under the same conditions, even mutants with 20% and 50% of wild-type GSH amounts are slightly stunted. The most severely compromised mutants, zir1 and rml1, were crossed with either gr1, which lacks cyto-nuclear glutathione disulfide reductase and was used to induce a pronounced shift in EGSH, or with bir6, which has a diminished glutathione consumption and thus exhibits slightly increased levels of GSH. Based on theoretical considerations, these levels are not expected to shift the EGSH to any significant extent. Our study shows that deleting GR1 in the zir1 or rml1 background does not result in an obvious phenotypic change. By contrast, deleting BIR6 was sufficient to suppress the growth arrest in rml1 and to attenuate the growth restriction in zir1. These findings demonstrate that root growth is dependent on the availability of sufficient amounts of GSH, and not affected by pronounced changes in EGSH. This insight provides a decisive step towards understanding the mechanisms underpinning the proposed role of glutathione in growth control.

Leaf inclination, an essential characteristic of ideal plant architecture, plays a crucial role in determining crop yield by influencing leaf area index and planting density. Brassinosteroid (BR) serves as the major phytohormone involved in leaf inclination regulation, while the mechanism of BR signaling regulation in rice still needs exploration when compared to Arabidopsis. Here, a bHLH transcription factor OsbHLH55 was highly expressed in the lamina joint, the osbhlh55 gene editing mutants exhibited large leaf inclination resulted from increased size of parenchyma cells on the adaxial side of the lamina joint, while OsbHLH55 overexpression lines showed small leaf inclination. In addition, the osbhlh55 mutants were hypersensitive to BR and the expression was inhibited by BR, suggesting that OsbHLH55 was negatively regulated by BR. Genetic experiments verify that OsbHLH55 can directly bind to the promoter of OsWRKY53 to repress its expression, which is involved in the BR signaling pathway. Moreover, OsbHLH55 can interact with and be phosphorylated by the OsMAPK6 in vitro. Collectively, our investigation revealed OsbHLH55 as a negative regulator of rice BR signaling to function in leaf inclination regulation, and shedding light on the intricate interplay between BR and MAPK signaling pathways in rice.

Circadian rhythms, driven by an endogenous biological clock, align physiological processes with the Earth's 24-hour light-dark cycle, enabling organisms to adapt to diurnal environmental changes. In plants, the circadian clock regulates key physiological and metabolic processes, such as photosynthesis, nutrient uptake, and stress responses, thereby optimizing growth and development. Recent studies reveal that lipid metabolism is significantly influenced by the circadian clock and diurnal rhythm, which modulate the expression of lipid metabolic genes and ensures rhythmic production and degradation of lipids in response to energy availability and environmental conditions. This review highlights the circadian and diurnal regulation of fatty acid biosynthesis and membrane (phospho/galactolipids), storage (triacylglycerols), and surface (waxes) lipid metabolism in plants, while addressing the broader implications for plant adaptation to environmental changes and extreme stress conditions.

Accumulating scientific insights reveal the ecological and evolutionary implications of phenotypic plant plasticity in response to biotic and abiotic stress factors. This study confirms that root-knot nematode infection leads to intergenerational acquired resistance (IAR) in rice offspring. Genome-wide and targeted gene expression analyses demonstrated that offspring of nematode-infected rice plants are better prepared to fight against such attack through 'spring loading' of hormone-related plant defense genes. These genes are suppressed under basal conditions in IAR plants but show a more dramatic induction upon nematode attack. Here, ChIP-sequencing was executed on the offspring of IAR versus naive plants to investigate if histone modifications could be involved in the spring-loaded expression pattern. This revealed enrichment of H3K4me3 on defence related genes and H3K27me3 on development-related genes in roots of IAR plants. Detailed bio-informatic analyses pointed towards significant epigenetic changes to the ABA, ET and MAPK signalling pathways in the offspring of nematode-infected plants. A rice line with reduced activity for OsMPK5 was found to be deficient in defense spring loading and the IAR phenotype. Transmitting a memory of encountered stress factors to one's offspring is arguably an important asset for the adaptation of sessile plant communities to hostile environments.

Sorghum grains are rich in protein and starch but exhibit low protein digestibility, limiting their value for food and feed. However, the molecular mechanisms underlying these traits remain largely unknown, particularly the roles of structural genes and transcription factors (TFs) hindering efforts to improve grain quality. To address this, we constructed a gene co-expression network using transcriptome data from grain development in two different field seasons. In parallel, we quantified starch and protein content and measured protein digestibility. Two major gene co-expression modules were identified. The first was linked to the loss of protein digestibility, involving genes related to disulfide bonds formation and modulation. The second contained most kafirin and starch metabolism genes, as well as orthologs of TFs known to regulate protein and starch accumulation in other species. Functional assays in protoplasts for six TFs suggest a central role for SbPBF1a, SbPBF1b and SbNF-YC13 in modulating the expression of genes involved in protein and starch biosynthesis. This study provides new insights into the transcriptional regulation of protein and starch accumulation in sorghum. It identifies candidate regulatory and structural genes that offer promising targets for future validation and for improving grain quality in breeding programs.

Nitric oxide (NO) is a plant gasotransmitter that regulates plant growth and development by interacting with different regulatory pathways. Among these, brassinosteroids (BRs) have become candidate phytohormones that interact antagonistically and closely with NO to regulate plant growth. Seedling growth in NO-deficient mutants is enhanced and hyper-responds to BR treatments, while NO over-accumulator mutants show some developmental defects. Interestingly, this hyper-response was also observed in mutants that had both constitutively activated BRs signalling and reduced NO levels. BR signalling mutants exhibited different responses to the NO repressive role in seedlings. The phenotypes observed were attributed to the induction of BR-repressed biosynthetic genes and the repression of BR-induced growth-promoting genes detected in NO over-accumulating plants, with opposite gene expression patterns detected in NO-deficient plants. Furthermore, the activation of BR signalling has an impact on NO accumulation, as BR-treated plants or mutants with activated BR signalling showed hyper-accumulation of NO. Finally, elevated endogenous levels of brassinolide, the most bioactive BR, were found in NO-deficient plants, which could explain the growth promotion observed in this mutant. These findings contribute to a better understanding of the growth-repressive role of NO during seedling development through its interaction with BR biosynthesis, signalling, and responses.

Circadian clocks have long been hypothesized to tightly link cellular and physiological processes to the appropriate time within the twenty-four-hour cycle of the earth's daily rotation. According to this hypothesis, circadian rhythms with cycle lengths that differ significantly from twenty-four hours would be disadvantageous, as they would generate a desynchronization between the endogenous and exogenous cycles that would place stress upon an organism through the required daily resetting at dawn. However, recent work has demonstrated that endogenous circadian cycles that differ from twenty-four hours by two hours or more are prevalent within the green lineage. Herein, we review recent work on the prevalence of and adaptive advantages associated with natural variation in circadian cycles. Based on known photoperiodic sensing mechanisms we also describe a set of principles that allow the same changes in circadian period to cause different plant responses. This fine-tuning of clock output pathways provides a flexible mechanism enabling plants to use a wide range of life history strategies for plant adaptation to different environmental niches. Further studies are needed to determine how variations of the clock and other signals are integrated in different plants. These studies highlight the circadian clocks' position as a prime adaptation target for migration of plant species into new environmental ranges.

The essence of multicellular life lies in the dynamic tension between unity and autonomy of individual cells achieved through diverse molecular and structural mechanisms. Plants have evolved plasmodesmata as an elegant solution to this fundamental challenge, creating cytoplasmic bridges that enable both local and systemic communication despite constraints imposed by their rigid cell walls. An emerging paradigm reveals that the core molecular machinery brings about context-dependent, multi-faceted regulation of plasmodesmal permeability through integration with various cellular signaling pathways. Regulation through callose accumulation and degradation has been established as the primary mechanism controlling plasmodesmal permeability. Recent studies now reveal that this regulation is signal-specific and mechanistically diverse, giving rise to the same apparent endpoint of closure with different biological outcomes depending on the signaling context. This creates biological specificity through convergence on shared callose-regulating mechanisms. Understanding how regulatory complexes assemble, achieve signal specificity, and integrate diverse cellular inputs represents a critical frontier in plant biology. In this review, we discuss the molecular players, regulatory mechanisms, and integrative signaling networks that support this paradigm.

Plants primarily acquire inorganic nitrogen (N) as nitrate (NO3-) and ammonium (NH4+). The uptake of these forms is strongly modulated by external pH, which influences both their availability and the activity of their specific root transporters (NRTs for NO3- and AMTs for NH4+). Moreover, NO3- and NH4+ uptake exert opposite effects on net proton (H+) fluxes, raising the question of how external H+ availability shapes the balance between both N forms and their reciprocal regulation. Using Arabidopsis knock-out mutants deficient in key NO3- and NH4+ transporters, in combination with N and H+ flux assays and gene expression analyses, this study shows that low external pH strongly promotes NO3- uptake but severely constrains plant growth under NH4+ nutrition. The stimulatory effect of external H+ overrides the H+ efflux typically induced by NH4+. Conversely, at higher external pH, an alternative, AMT-independent transport mechanism likely related to K+ transport appears to facilitate NH4+ uptake and mitigate its toxicity. Furthermore, mutants lacking AMTs exhibited enhanced high-affinity NO3- uptake at low pH, while the NRT1.1 mutant (chl1-5) showed increased high-affinity NH4+ acquisition at higher pH. These findings highlight a new and complex interplay between pH and reciprocal N uptake dynamics and point to AMT- and NRT1.1-independent pathways contributing to the acquisition of alternative N forms under contrasting pH conditions.

Nitrogen is as a crucial macronutrient necessary for plant development. Legumes form well-known symbiotic relationships with nitrogen-fixing bacteria, but non-leguminous plants such as Arabidopsis thaliana also gain advantages from these associations without developing nodules. This study examines the relationship between A. thaliana and Sinorhizobium meliloti when conditions contain extremely low nitrogen levels. According to our findings, functional evidence consistent with biological nitrogen fixation from S. meliloti enhances plant growth and root system development. The plant growth response needs two essential regulatory genes, NSP1 and NLP9, which become active exclusively in nitrogen-deficient conditions. Microscopy showed bacterial colonization on the root epidermis, and subsequent analysis identified NSP1 and NLP9 as mediators of plant signaling, which modulate the host program to allow S. meliloti's nitrogenase activity. NSP1 controls the induction of NLP9, indicating a conserved signaling pathway resembling that found in legumes. The study discovered a non-canonical interaction beyond nodules that regulates bacterial nitrogen fixation functionality and improves A. thaliana survival during nutrient scarcity. The research expands our comprehension of how plants interact with nitrogen-fixing bacteria and indicates conserved molecular systems that allow non-leguminous plants to form advantageous relationships under severe nitrogen scarcity.