Journal of Experimental Botany最新文献

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.

The legume Lotus japonicus expresses nine hemoglobins, including leghemoglobins (Lbs), class 1 phytoglobin (Glb1-1), and an unusual phytoglobin (Glb2-1). Quantitative PCR, proteomics, and plant mutant analyses indicated that Glb2-1 is mainly present in nodules without replacing Lb function, but is also in roots and photosynthetic tissues. Comparison of hormonal profiles of the knock-out mutants glb1-1, glb2-1, and glb1-1/2-1 showed that Glb1-1 and Glb2-1 have distinct functions. The increase of salicylic acid in the leaves of glb1-1 revealed a role of Glb1-1 in the defense response, which was corroborated by accumulation of pipecolic acid, a metabolite involved in plant immunity. In contrast, the decrease of bioactive jasmonoyl-isoleucine in glb2-1 was consistent with a role of Glb2-1 in the plant's reproductive stage. The mutants also showed changes in cytokinins, gibberellins, and polyamines, but without clear distinctive patterns. The crystal structure of Glb2-1 was determined to 1.6 Å resolution and compared with those of soybean Lba and Arabidopsis Glb1. In combination with mutant versions of Glb2-1, residues Tyr31, His64, and Cys65 were identified as critical for O2-binding stability. Spectral changes in heme coordination when Tyr31 is substituted for Phe highlights the importance of the residue at the B10 position for Lb and Glb function.

Alfalfa (Medicago sativa L.) is a key forage crop valued for its adaptability and nutritional quality, yet salinity significantly limits its productivity, particularly in arid regions. Understanding early stress responses is crucial for improving resilience. Salt stress impairs leaf growth and photosynthesis, triggering complex, time-dependent signaling. Sucrose non-fermenting kinase 1 (SnRK1), a central metabolic sensor, regulates metabolism and growth under stress. We investigated the dynamics of SnRK1, sucrose, and trehalose-6-phosphate (Tre6P) during leaf expansion in a salt-tolerant alfalfa cultivar. Plants were hydroponically grown and exposed to 200 mM NaCl. Stress induced transient declines in chloroplast performance (Fv/Fm, performance index). SnRK1 activity peaked within 1 hour post-treatment (hpt), probably initiating metabolic shifts. By 3 hpt, sugar metabolism shifted, with increased catabolism, modulation of the tricarboxylic acid cycle, and glucose-6-phosphate accumulation. SnRK1 and sucrose showed opposing wave-like patterns, with sucrose peaking at 1 day post-treatment (dpt) as Tre6P declined, indicating a disrupted regulatory link. A second SnRK1 peak at 3 dpt correlated with reduced leaf growth. Exogenous sucrose suppressed salt-induced SnRK1 activity. This is the first report of wave-like SnRK1 activation and Tre6P-sucrose uncoupling in alfalfa, highlighting early SnRK1 activation as key to salt stress adaptation.

Ultraviolet-B (UV-B) light, a natural component of sunlight, plays a crucial role in the regulation of plant growth and development. B-box (BBX) proteins are zinc-finger transcription factors essential for plant growth, development, and responses to abiotic stress. The role of BBX5 in UV-B stress responses has not been previously identified. Here, we identify BBX5 as a novel regulator of UV-B stress tolerance in Arabidopsis. Firstly, UV-B treatment significantly induced the expression of BBX5. Transcriptome analyses revealed that BBX5 was associated with the anthocyanin biosynthesis pathway. Phenotypic analysis showed that bbx5 mutant exhibited heightened UV-B sensitivity and reduced anthocyanin levels under UV-B exposure, whereas BBX5-overexpressing lines displayed increased anthocyanin content and enhanced UV-B resilience. Mechanistically, BBX5 directly interacts with the promoter of anthocyanidin synthase (ANS), thereby stimulating its expression. HY5, a key regulator in UV-B signaling, enhances the expression of BBX5 by binding to its promoter region. Genetic analysis showed that BBX5 overexpression partially restored anthocyanin levels and improved UV-B resistance in hy5-215 mutant. Our study highlights the crucial role of the HY5-BBX5-ANS regulatory axis in modulating anthocyanin biosynthesis and UV-B acclimation in Arabidopsis.

Photosynthetic organisms have evolved diverse strategies to adapt to fluctuating light conditions, balancing efficient light capture with photoprotection. In green algae and land plants, this involves specialized light-harvesting complexes (LHCs), non-photochemical quenching, and state transitions driven by dynamic remodeling of antenna proteins associated with PSI and PSII. Euglena gracilis, a flagellate with a secondary green plastid, represents a distantly related lineage whose light-harvesting regulation remains poorly understood. Although spectral shifts under different light regimes have been observed, their molecular basis has been unknown. Here, through integrated phylogenomic, proteomic, structural, and spectroscopic analyses, we identify a novel chlorophyll a far-red-absorbing antenna complex in E. gracilis, composed of euglenozoa-specific Lhce proteins. This LHCE antenna complex forms a pentameric complex under low light and transiently associates with PSII during far-red light exposure. It is structurally and functionally distinct from canonical LHCII trimers and absent in Viridiplantae. Additionally, PSI in E. gracilis is surrounded by an expanded belt of Lhce and LhcbM proteins around a minimal core. These findings reveal a unique mechanism for regulating PS antenna size in E. gracilis that is distinct from known models in plants and green algae, and highlight an alternative evolutionary strategy for light acclimation in organisms with secondary plastids.

The FW2.2-LIKE/CELL NUMBER REGULATOR (FWL/CNR) gene family comprises PLAC8 domain-containing membrane-associated proteins and was named in reference to its founding member, the FW2.2 gene, which determines fruit size in tomato via a negative regulation on cell divisions. The function of PLAC8 domain-containing FWL/CNR proteins in plants remains largely unexplored. Only recently has the molecular and cellular mechanism of FW2.2 been described as regulating plasmodesmata-mediated cell-to-cell communication. In the present study, we provided a functional analysis of SlFWL genes in tomato, aiming at investigating any direct role in the control of organ growth. Based on a combination of molecular and cellular approaches, we selected three SlFWL proteins, namely SlFWL2, -4, and -5, which are localized at the plasma membrane. Gain- and loss-of-function transgenic plants were generated to explore their putative role as regulators of organ growth in tomato. This allowed us to shed light more specifically on the critical involvement of SlFWL5 in leaf and hypocotyl development. We show here that SlFWL5 is localized at plasmodesmata, and that it regulates leaf size and morphology, and hypocotyl growth, by promoting cell expansion-unexpected for a CELL NUMBER REGULATOR protein. This original finding underscores further the importance of some FWL/CNR family members in growth regulation.

Kernel hardness is an important indicator of quality in sweet corn (Zea mays subsp. saccharata), but the mechanism underlying its regulation remains poorly understood. In this study, we determined that the starch and protein composition of the endosperm was positively correlated with kernel hardness. AGPL2, encoding a subunit of AGPase, was differentially expressed in the endosperm of different cultivars and was responsible for residual AGPase activity and starch biosynthesis. We found that Opaque2 (O2), a key regulatory transcriptional factor for endosperm development, directly binds to the promoter of AGPL2 and activates its expression, resulting in the accumulation of starch. Taken together, our results reveal a novel mechanism whereby the O2-AGPL2 module participates in regulation of kernel hardness in sweet corn.

Carotenoids are essential for chloroplast development, with lycopene β-cyclase as the rate-limiting enzyme in the biosynthesis of β-carotene and α-carotene. This study investigates the carotenoid biosynthetic alterations in a low-temperature-sensitive zebra-leaf rice mutant, oslsz1, which exhibits yellow or yellow-green striped leaves before the five-leaf stage at lower temperatures (22 °C and 28 °C) but develops normally at higher temperature (34 °C). Metabolomics revealed that at 22 °C, levels of β-carotene and xanthophylls decreased, while levels of (E/Z)-phytoene, lycopene, α-carotene, and γ-carotene increased in oslsz1 as compared with the wild type. Transmission electron microscopy demonstrated defective chloroplast development in oslsz1 at 22 °C. Through map-based cloning, the causative gene was identified as OsLCYb, which encodes lycopene β-cyclase with a V232M missense mutation. mRNA quantification showed that OsLSZ1/OsLCYb is ubiquitously expressed, especially in young-seedling leaves, with suppression at low temperatures. Heterologous expression of oslsz1/oslcyb in Escherichia coli confirmed a near-complete loss of lycopene conversion to β-carotene at 22 °C. Further domain dissection indicated that the N-terminal 181 amino acids of OsLSZ1/OsLCYb are critical for low-temperature sensitivity, while its C-terminal extension enhances this response. In summary, these findings underscore the crucial role of OsLSZ1/OsLCYb in carotenoid biosynthesis and chloroplast development in rice at low temperatures.

Potato tuber dormancy is influenced by genetic, environmental, and management factors. This review critically reassesses the current understanding and terminology of factors affecting dormancy phases in potatoes, emphasizing the need for alignment with concepts used in other dormant model systems, and refocusing on the practical implications for commercial storage and breeding. Many hypotheses exist on the subject of potato tuber dormancy. The timing of endodormancy initiation has been a subject of debate for the last few decades, and differs in comparison to other model dormant systems. Gene expression studies have identified numerous potential markers for dormancy phases, yet inconsistencies in dormancy terminology and experimental storage conditions make it challenging to interpret the literature. We suggest refining the term 'ecodormancy' by distinguishing dormancy under cool storage (ware tubers for processing market) as 'store quiescence', and under cold storage (ware table-stock and seed tubers) as 'chilling response', to improve understanding and management of dormancy in different storage scenarios. Key knowledge gaps remain for the role of ethylene, regulation of reactive oxygen species, role of Dormancy Associated MADS-box genes, and the mechanisms for apical dominance. Addressing these gaps could enhance breeding strategies and optimize storage management, ultimately supporting improved commercial potato production and supply.

Trehalose 6-phosphate (Tre6P) is a signalling metabolite that maintains sucrose homeostasis and links plant growth and development to the availability of sucrose. Most of our knowledge of the nexus between Tre6P and sucrose comes from studies on arabidopsis (Arabidopsis thaliana), and it is unclear whether this close relationship is generally conserved across other species. To address this question, we investigated the diel changes in sucrose and Tre6P in leaves from a phylogenetically diverse set of angiosperms with different phloem loading and carbohydrate storage strategies: arabidopsis, Alchemilla molis, strawberry (Fragaria×ananassa), Plantago major, melon (Cucumis melo), and wheat (Triticum aestivum). Despite large differences in their sucrose and Tre6P levels, there were positive correlations between sucrose and Tre6P across all species. Network analysis confirmed a strong association between Tre6P and sucrose in all species, and also revealed a common link with malate, consistent with positive regulation of malate synthesis by Tre6P. In combination with previous observations that Tre6P is synthesized in and around the leaf vasculature, our findings suggest that Tre6P primarily reflects the vascular transport pool of sucrose in leaves. We conclude that the sucrose-Tre6P nexus is widespread among angiosperms, with a conserved role in regulation of sucrose metabolism and transport.