Journal of Experimental Botany最新文献

Cyanobacteria rely on bicarbonate (HCO3-) as the primary inorganic carbon (Ci) source for photosynthesis in aquatic environments. To use this Ci source, cyanobacteria employ CO2 concentrating mechanisms that elevate cytoplasmic HCO3- via plasma membrane transporters, enhancing carboxylation by carboxysomal Rubisco. The sodium-dependent SbtA1 transporter family is well-characterized in freshwater cyanobacteria, but the related SbtA2 family, prevalent in marine α-cyanobacteria, remains uncharacterised. Here, we report functional characterisation of SbtA2 homologues from marine Synechococcus spp., which exhibit high Ci uptake flux with apparent chloride dependence and intermediate HCO3- affinity (K0.5 ≈ 150 µM), when assessed in E. coli. SbtA2 achieved internal Ci accumulation up to 24 mM within 30 seconds. Co-expression with the putative regulator SbtB2 reduced uptake activity, suggesting a regulatory role for this protein. These findings indicate that SbtA2 transporters contribute significantly to carbon acquisition in marine cyanobacteria. Given potential to enhance CO2 supply to Rubisco in C3 plants, we targeted SbtA2 to the tobacco chloroplast inner envelope membrane; however, this did not improve photosynthesis or growth. Our results highlight the functional diversity of cyanobacterial Ci transporters and suggest that additional components may be required for effective transfer of such systems into plant chloroplasts.

Inorganic nitrogen (N) is known to influence the composition and functioning of ectomycorrhizal (ECM) fungal communities. Research consistently highlights fungal traits related to carbon (C) use as key determinants of fungal sensitivity to elevated inorganic N, with more C-demanding ECM fungi declining along inorganic N gradients. This decline is often attributed to reduced C allocation from host trees to their fungal symbionts, yet the precise mechanisms underlying this reduction remain unclear, despite significant research efforts. Here, I examine recent advances in this field which highlight the role of fungal nutritional requirements and source-sink dynamics in regulating C flow to ECM fungi. Additionally, I explore how N-induced shifts in ECM fungal communities impact biogeochemical cycles, potentially leading to globally significant changes in decomposition and C-sequestration rates in forest soils. Given the scale of these potential effects, further research is essential to fully understand the complexity of N-driven changes in ECM fungal functioning.

Flowering is a critical trait for reproduction and survival in plants, influenced by both temperature and photoperiod. Here, we explored the molecular basis of temperature- and photoperiod- insensitive flowering in the Arabidopsis natural accession IP-Svi-0. We identified genetic variations underlying the early flowering of IP-Svi-0 using whole-genome and RNA sequencing and verified them by generating transgenic plants that complemented or silenced the responsible genes. The complete insensitivity of IP-Svi-0 to temperature and photoperiod is due to its unique combination of polymorphisms at loci encoding floral repressor genes FLOWERING LOCUS C (FLC) and MADS AFFECTING FLOWERINGs (MAFs). Our data revealed that IP-Svi-0 carries large deletions in FLC, MAF2, and MAF3, resulting in gene knockouts. It also harbors promoter polymorphisms in FLM and MAF5, leading to reduced gene expression. This misregulation of the FLC-MAFs module causes de-repression of the floral activators FT and SOC1, resulting in unregulated early flowering. Flowering-time analysis showed that the fck (silenced MAF2-5 with flc flm mutations) phenocopies IP-Svi-0, and restoring FLC, MAF2, or MAF3 effectively delays its early flowering. Our findings indicate that temperature and photoperiod signals are integrated into the FLC-MAFs regulatory module to control flowering time in natural accessions. These results suggest a promising strategy to overcome seasonal barriers to flowering.

The role of stems as a source of nitrogen (N) for the growing seeds has received little attention in soybean. This study evaluated N storage and mobilization from stems to seeds across 42 high-yielding environments under contrasting N supply: a "zero-N" treatment, in which crops relied on soil and biological N fixation, and a "full-N" treatment that received ample N fertilizer. We measured the accumulated N per organ before seed filling and subsequent N mobilization from vegetative organs to the seed. Vegetative storage protein (VSP) abundance in stems was quantified via proteomics. Average yield ranged from 4.2 to 7.3 Mg ha-1, with +11% yield in full-N (6.1 Mg ha-1) compared to zero-N (5.5 Mg ha-1). The full-N treatment resulted in a larger mobilized N from stems (+42%) and leaves (+22%) to seeds than the zero-N treatment, which was attributed to the larger N stored in stems and leaves before seed filling (+37% and +21%, respectively). Among the 5,335 identified proteins at the peak of N accumulation, VSPα (+1.4%) and VSPβ (+0.8%) showed the highest increase in full-N. We conclude that N stored in stems as VSPs before seed filling plays a key role in meeting the seed N demand in high-yielding soybean crops.

Lactate dehydrogenases are oxidoreductases present in almost all living organisms. They catalyze the interconversion of pyruvate and L-lactate with simultaneous oxidation of NADH and reduction of NAD+. Since their function remains largely unexplored in rice, in this study we deciphered the role of the rice lactate dehydrogenase, OsLdh3. OsLdh3 showed optimum enzyme activity at pH 6.6 for the forward reaction (pyruvate to L-lactate) and pH 9 for the reverse reaction (L-lactate to pyruvate). Protein-protein interaction studies revealed that OsLdh3 interacts with the glycolytic enzymes glyceraldehyde 3-phosphate dehydrogenaseC3 (OsGAPC3) and Enolase2 (OsLos2), suggesting its role in regulating glycolytic flux. Further, overexpression of OsLdh3 in rice showed enhanced abiotic stress tolerance by exhibiting elevated NAD+ levels and OsGAPC3 activity, thereby facilitating an improved glycolytic continuum and higher pyruvate accumulation. Consequently, these lines also showed increased mitochondrial respiration and ATP synthesis, and reduced reactive oxygen species (ROS) accumulation. Further, enhanced photosynthetic efficiency and reduced yield penalty of the stress-imposed OsLdh3 overexpression lines underscore its importance in crop productivity under adverse climatic conditions. Thus, our findings show that OsLdh3 enhances stress tolerance in rice by regulating redox homeostasis and respiration, reducing ROS levels, and maintaining energy balance. This makes OsLdh3 a promising candidate gene for developing climate-resilient rice cultivars with reduced yield gap.

The cuticle is a hydrophobic barrier limiting water loss and pathogen entry. Although light influences cuticle formation, the underlying mechanisms remain poorly understood, particularly in fruits. Here, we show that fruits from tomato (Solanum lycopersicum) plants grown under far-red-enriched light conditions displayed increased cuticle load due to the up-regulation of cutin and wax biosynthetic genes. Both tomato PHYB-encoding genes (SlPHYB1 and SlPHYB2) were implicated as negative regulators of fruit cuticle formation, as revealed by the thinner cuticles, reduced abundance of cutin monomers and cuticular waxes, and downregulation of cuticle-related genes detected in fruits from transgenic plants overexpressing constitutively active alleles of SlPHYB1/B2 (SlYHB1OE and SlYHB2OE). The impaired cuticle of SlYHB1/B2OE fruits resulted in increased susceptibility to Botrytis cinerea, despite their markedly enhanced flavonoid accumulation in the peel. PHYTOCHROME-INTERACTING FACTORs (SlPIF3, SlPIF4) and the B-box protein SlBBX28 were identified as downstream factors of SlPHYB1/B2-mediated regulation of cuticle deposition, synergistically activating the expression of cuticle-related genes. Additionally, SlPHYB1/B2 signaling also downregulated multiple central carbon metabolism-related genes in the fruit peel, likely reducing the pool of activated fatty acids (FAs) feeding into cutin and wax biosynthetic pathways. Together, our results uncover a novel regulatory layer of light signaling in fleshy fruits, revealing that, besides controlling fruit nutritional traits, the PHYB-PIF-BBX regulatory module also shapes the fruit cuticle formation.

Reprogramming of differentiated root cortical cells into proliferative stem cells is the prerequisite for legume nodule organogenesis, yet the molecular trigger that confers stem-cell identity upon these cortical cells remains elusive. Here we demonstrate that, in soybean (Glycine max), the canonical root stem-cell regulator WUSCHEL-RELATED HOMEOBOX gene WOX5 is activated by rhizobia specifically in cortical cells that will give rise to nodule primordia. CRISPR/Cas9-mediated knockout of the three WOX5 homologs, wox5abc mutants reduced nodule number and attenuated nitrogenase activity, attributable to a decrease in primordium density rather than impaired rhizobia infection. Promoter dissection identified a 442 bp legume-specific promoter fragment within the WOX5a promoter that is both necessary and sufficient for primordium-specific expression. Chromatin immunoprecipitation and dual-luciferase assays revealed that this promoter fragment is directly bound by the symbiosis-responsive transcription factor NF-YAc to activate expression of WOX5a. Loss of NF-YAc phenocopied wox5abc, and NF-YAc overexpression failed to rescue nodulation in wox5abc mutants. Collectively, our findings reveal that NF-YAc-mediated activation of WOX5 initiates a de novo stem-cell niche in root cortical cells, providing the critical developmental trigger for nodule primordium initiation in soybean.

In plants, nitrogen and carbon metabolism are tightly interconnected, and nitrogen availability often negatively correlates with phenylpropanoids that are associated with wood formation and stress responses. A nitrate transporter 1/peptide transporter (NRT1/PTR) family (NPF) gene (PtNPF6.1), which is expressed in the vasculature, was previously found to have a genetic association with the variation in syringyl lignin content in poplar trees (Populus trichocarpa). PtNPF6.1 belongs to an evolutionarily distinct NPF superfamily with limited taxonomic distribution. RNAi-mediated suppression of PtNPF6.1 led to increases in total foliar nitrogen and amino acids related to nitrogen transport and storage in source leaves. There was also a concomitant decrease in soluble phenolics, including attenuated stress-induced production of anthocyanins and condensed tannins. The proportions of syringyl and p-hydroxyphenyl units in lignin were slightly but significantly decreased in downregulated lines grown under high nitrogen conditions, while there was an increase in the level of ester-linked p-hydroxybenzoate groups. Together, these results suggest that PtNPF6.1 is involved in maintaining internal nitrogen homeostasis in trees, indirectly impacting the production of nitrogen-free phenolics including lignin and soluble secondary metabolites.

Root-knot nematodes (RKNs) pose a major threat to global crop production, yet the molecular mechanisms underlying plant resistance to RKN infection remain incompletely understood. Here, we identify a small-secreted effector from Meloidogyne incognita, Mi-MSP5, as an avirulence determinant that enhances tomato resistance through targeted modulation of host lipoxygenase activity. Transgenic tomato hairy roots overexpressing Mi-MSP5 exhibited approximately 50% reduction in susceptibility, indicating a strong defense-promoting role. Yeast two-hybrid screens of nematode-induced tomato gall prey library identified the lipoxygenase homology protein LOXH1 as a specific Mi-MSP5 interactor. LOXH1 and Mi-MSP5 colocalized and interacted at the plasma membrane in planta, and LOXH1 expression was transiently upregulated during early stages of nematode infection. Functional assays revealed that LOXH1 overexpression phenocopied Mi-MSP5-mediated resistance, whereas partial silencing of LOXH1 increased susceptibility. Biochemical analyses demonstrated that both Mi-MSP5 and LOXH1 overexpression led to approximately a twofold increase in lipoxygenase enzymatic activity in roots. Moreover, this activation correlated with enhanced expression of jasmonic acid (JA)-responsive defense genes. Collectively, our findings uncover a novel effector-triggered immunity mechanism in which a nematode effector co-opts a non-catalytic host lipoxygenase domain protein to boost lipoxygenase activity and activate JA-mediated defenses, providing a promising strategy for engineering durable nematode resistance in plants.

Sucrose is the central unit of carbon and energy in plants. As the product of photosynthesis, it is transported from source to sink tissues across short and long distances. Subcellular sucrose concentrations strongly influence rates of transport within cells, tissues and organs. Moreover, as a central metabolite, its concentration influences the rates of many enzymatic reactions. Measuring sucrose concentration with subcellular resolution remains challenging, especially for the cytosol, which hosts many critical enzymatic reactions and, in many cells, occupies only a thin layer between the vacuole and the plasma membrane. Here, we review the methods that have been utilized to measure subcellular sucrose concentrations in plant cells. The approaches covered include microautoradiography, non-aqueous fractionation, Fourier transform infrared (FTIR) microspectroscopy, Raman microspectroscopy, mass spectrometry imaging, FRET nanosensors, direct sampling, and theoretical modeling. We provide perspectives on the use cases for these methods and discuss developments towards resolving subcellular sugar concentrations in live tissues.