The Plant Journal最新文献

Brassinosteroids (BRs) are essential phytohormones that regulate plant growth and development, including hypocotyl elongation in Arabidopsis thaliana. Although the core BR signaling components have been well characterized, the mechanisms that control the nuclear localization and stability of key transcription factors such as BZR1 and BES1 remain less understood. Here, we identify IMPORTIN BETA 4 (IMB4) as a critical regulator of BR-mediated hypocotyl elongation. Loss-of-function imb4-1 mutants exhibit reduced hypocotyl elongation in the dark and display reduced sensitivity to exogenous brassinolide and enhanced sensitivity to the BR biosynthesis inhibitor brassinazole. IMB4 physically interacts with BZR1 and BES1, promotes their nuclear accumulation, and enhances their stability by protecting them from 26S proteasome-mediated degradation. Genetic analysis shows that the bzr1-1D and bes1-1D alleles partially rescue the imb4-1 hypocotyl phenotype, and expression of BR-responsive genes is reduced in imb4-1 but restored by bzr1-1D. Mechanistically, IMB4 interferes with the interaction between BIN2 and BZR1/BES1, thereby inhibiting their degradation. Moreover, IMB4 expression is induced by BR treatment, suggesting a positive feedback loop. Our findings uncover a previously unrecognized role for IMB4 in regulating BR signaling and highlight the importance of nuclear transport machinery in hormone-mediated developmental programs.

Citrus fruit accumulates acid at the early stage of fruit enlargement and sugar at the fruit maturity stage. Drought stress during these stages accelerates their accumulation. Here, we reported a citrus circadian clock gene, CIRCADIAN CLOCK ASSOCIATED 1 (CsCCA1), which exhibits circadian rhythmicity and impacts citrate accumulation in citrus fruit under drought stress, even naturally working in cultivars with high or low fruit citrate levels. Further, it was found to participate in fruit sugar accumulation. Overexpression of CsCCA1 in citrus juice sacs, calli, leaves, and tomato fruits was associated with an increase in the concentration of citrate, sucrose, fructose, and glucose, whereas the silenced lines showed the opposite effect. The higher concentrations of citrate and sugar enhanced the drought tolerance of citrus callus. We also found that CsCCA1 positively regulates the bHLH transcription factor ANTHOCYANIN 1 (AN1), which plays a role in citrate transport to the vacuole, and sucrose transporter 1 (SUT1), which facilitates the entry of sucrose into cells. This regulation occurs through the binding of CsCCA1 to the evening element sequences in their promoters. This indicates the circadian clock's role in coordinating drought signal with the accumulation of citrate and sugar, providing novel insights into the formation of citrus fruit quality.

Nannochloropsis oceanica is an industrially relevant marine microalga that accumulates high levels of lipids and synthesizes the health-beneficial ω-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA). However, EPA biosynthesis in this alga is constrained by inefficient conversion of abundant C16 fatty acids into the C18 precursors required for downstream desaturation and elongation reactions. Here, we identified NoELO2, a low-abundance fatty acid elongase, as a key regulatory enzyme controlling early carbon flux into EPA biosynthesis in N. oceanica. Heterologous expression in yeast demonstrated that NoELO2 catalyzed elongation of C16 to C18 fatty acids. Subcellular localization revealed that NoELO2 resided in the chloroplast-associated endoplasmic reticulum, positioning it at a strategic interface between plastidial fatty acid synthesis and extraplastidial lipid metabolism. Boosting NoELO2 expression in N. oceanica substantially enhanced EPA accumulation without compromising growth. EPA content reached up to 66.1 mg/g dry weight (49.2% increase)-the highest value reported in transgenic N. oceanica achieved through manipulation of a single endogenous enzyme. Conversely, knockout of NoELO2 reduced EPA levels and triggered compensatory transcriptional changes in other elongase genes. Together, our results identify NoELO2 as a critical metabolic gatekeeper that alleviates a previously underappreciated C16 bottleneck in EPA biosynthesis. This work provides both mechanistic insight into fatty acid flux control in microalgae and a practical metabolic engineering strategy for improving ω-3 fatty acid production.

Potassium (K) is classically viewed as a guard-cell osmoticum, yet its influence on the photosynthetic efficiency under steady-state and fluctuating light remains unresolved. We combined gas exchange, cellular anatomy, and transcriptomic profiling to explore how K deficiency limits CO₂ assimilation (A_N) in tomato (Solanum lycopersicum). Contrasting our expectations, the decline of A_N and mesophyll conductance (g_m) under K deficiency in tomato was not attributed to alternation of leaf and cellular anatomy but was linked to downregulation of carbonic anhydrases and plasma-membrane aquaporins that facilitate CO₂ diffusion. The maximum carboxylation rate of Rubisco (V_cmax) declined in parallel, coinciding with the repression of Rubisco small-subunit genes and Rubisco activase. Under fluctuating light, K deficiency significantly slowed stomatal opening and accelerated stomatal closure, increasing potential loss of CO₂ fixation after transition from low to high light. Transcript data implicated K-transport, anion-channel, and sugar-transporter genes as the molecular brakes. Therefore, leaf K content influences photosynthesis by regulating diffusional and biochemical capacities. These findings highlight the importance of K in photosynthesis under both stable and variable light environments, offering new targets for improving crop photosynthetic resilience.

The rapid alkalinization factor (RALF) family of small signaling peptides regulates diverse physiological and developmental processes in plants. RALF peptides influence cell wall remodeling and hormonal homeostasis through interactions with CrRLK1L malectin-like receptor kinases and leucine-rich repeat extensin (LRX) proteins anchored to the cell wall. Fruit ripening, characterized by coordinated hormonal regulation and extensive pectin remodeling, provides a relevant yet understudied context for this signaling module. Across fleshy fruits, CrRLK1Ls are expressed during fruit development and ripening but show diverse functions: tomato SlCrRLK1L20 promotes ripening by enhancing ethylene biosynthesis, whereas strawberry FaMRLK47 and peach PpTHE1 repress ripening by dampening ABA and ethylene, respectively. RALF33-like peptides increase susceptibility to fruit fungal pathogens, highlighting a trade-off between softening and defense. Overall, the RALF and CrRLK1L signaling network emerges as a conserved but flexible regulator linking cell wall dynamics, hormonal balance, and pathogen responses during fruit ripening.

Ziziphus jujuba Mill. 'Dongzao' ('Dongzao') is the most widely planted fresh jujube cultivar in China. Ziziphus jujuba Mill. 'Riguang' ('Riguang'), obtained through colchicine-induced mutagenesis, exhibits superior fruit size and quality compared to 'Dongzao', but its significantly reduced cold tolerance limits large-scale cultivation. To elucidate the molecular mechanisms underlying the differential cold tolerance between 'Dongzao' and 'Riguang', we examined the expression levels of ZjCML41, ZjCBF1, ZjCBF3, and ZjICE2, which were significantly upregulated in 'Dongzao' relative to 'Riguang'. Overexpression of ZjCML41 in Arabidopsis and jujube increased cold tolerance, whereas transient silencing of ZjCML41 in jujube decreased cold tolerance. Additionally, ZjbZIP25 could interact with the promoter region of ZjCML41 and positively regulate its expression, thereby enhancing cold tolerance. Moreover, ZjCML41 interacted with ZjIQD15, which in turn positively influenced cold tolerance by modulating the ICE-CBF pathway and reactive oxygen species scavenging activity. The proposed regulatory module comprising ZjbZIP25, ZjCML41, and ZjIQD15 enhances cold tolerance in 'Dongzao' by activating the ICE-CBF pathway, while downregulation of these genes reduces cold tolerance in 'Riguang'. These findings provide valuable theoretical insights and potential practical strategies for improving and regulating cold tolerance in 'Riguang'.

Stem cell fate in plants and animals is controlled by their niches. The mechanisms that determine the organization and maintenance of niches within the developing shoot apical meristem (SAM) are not well understood. Here, we report the role of NAC062, a membrane-localized transcription factor, in preserving niche functionality by regulating cytokinin (CK) signaling. Genetic and molecular evidence suggest that NAC062 affects the expression of AHK4, a receptor gene crucial to CK signaling in niche cells. NAC062 undergoes cleavage in response to cold stress in the SAM, thereby integrating environmental signals to control stem cell niche activity. Explants that express a constantly active form of NAC062 show greater shoot regeneration, which suggests that CK signaling is heightened within the regenerating tissue. Our analyses of NAC062 target genes highlight its role in shoot system development, senescence, and responses to abiotic stress. We provide a framework for understanding the maintenance of CK signaling homeostasis within the Arabidopsis SAM stem cell niche under normal and stress conditions.

Plants interact with their surrounding environment through the perception of a vast and structurally diverse array of volatile organic compounds (VOCs); however, the molecular mechanisms involved remain mostly unknown. Despite the large number of VOCs emitted and perceived by plants, only a small number of phylogenetically distinct, but often structurally similar receptors and receptor-like proteins have been identified and characterized to date. In this review, we summarize the current knowledge on plant VOC perception, with an emphasis on the receptors involved, including their structural characteristics and ligand specificities, as well as how distinct VOC signals can be translated into different downstream physiological responses. We further highlight the involvement of KARRIKIN INSENSITIVE 2 (KAI2)-mediated signaling in the perception of volatile compounds and their derivatives, discussing its potential role in expanding the repertoire of plant VOC perception mechanisms.

Polycomb Group (PcG) proteins, including members of Polycomb Repressive Complex 1 and 2 (PRC1 and PRC2), regulate many key developmental processes through transcriptional gene repression. While the molecular mechanisms of PRC2 and its histone methyltransferase involved in depositing histone 3 lysine 27 trimethylation (H3K27me3) are well understood, the components and E3 ubiquitin ligase functions of PRC1 in plants remain largely elusive. In Arabidopsis, AtRING1 is a key PRC1 component, containing an N-terminal RING-finger domain and a C-terminal RAWUL domain. Previous studies have relied on T-DNA insertion mutants in the investigation of AtRING1 function. By editing AtRING1A using CRISPR/Cas9 technology in the atring1b-1 background, here we have generated and characterized one N-terminal stop mutant atring1^ko and two C-terminal deletion mutants atring1^{▵C-terminal} lacking the RAWUL domain. We show evidence that atring1^ko represents the strongest loss-of-function mutant, exhibiting embryonic callus-like structures, demonstrating the essential role of AtRING1 in cell differentiation. Remarkably, the atring1^{▵C-terminal} mutants exhibit mild developmental defects, suggesting that the RING domain alone retains partial function, while the RAWUL domain fine-tunes PRC1 activity. Our molecular analyses support a model in which AtRING1/PRC1-mediated H2A monoubiquitination (H2Aub1) often precedes PRC2-mediated H3K27me3 deposition at some target loci. Strikingly, the RAWUL domain is required for efficient H2Aub1 enrichment and influences H3K27me3 deposition in a locus-specific manner. Taken together, our study provides new insights into the molecular mechanism underlying PRC1 E3 ligase activity, supporting that PRC1 function facilitates PRC2 activity in epigenetic gene silencing.

De novo DNA methylation, orchestrated by the RNA-directed DNA methylation (RdDM) pathway, is essential for gene regulation and transposon silencing. While CLASSY (CLSY) proteins facilitate RNA POLYMERASE IV (Pol IV) recruitment to initiate the RdDM pathway in plants, their roles in crops are incompletely explored. Here, we report OsCLSY4 as the dominant regulator within the OsCLSY family, driving Pol IV-mediated epigenomic patterns and influencing diverse agricultural traits. Epigenomics analyses reveal that OsCLSY4 controls over 95% of Pol IV-dependent 24-nucleotide small interfering RNA (24-nt siRNA) clusters and more than 70% of Pol IV-dependent hypomethylated CHH differentially methylated regions (DMRs), predominantly at miniature inverted-repeat transposable elements (MITEs). Loss of OsCLSY4 leads to dysregulation of MADS22 and GA20ox1 in a DNA methylation-dependent manner. SunTag-mediated targeted demethylation confirms that reduced DNA methylation in promoter regions leads to MADS22 activation and GA20ox1 repression to influence grain size, linking epigenetic changes to phenotypic outcomes of osclsy4. Moreover, OsCLSY4 governs tissue-specific methylation patterns in panicle and seedling. Mechanistically, OsCLSY4 is the predominantly expressed OsCLSY family member and interacts with Pol IV. Collectively, our findings position OsCLSY4 as a central hub for Pol IV-mediated epigenomic regulation in rice and suggest its potential utility in epigenetic breeding strategies.