Journal of Experimental Botany最新文献

Production of secreted leaf bud resin is a mechanism for temperate trees to protect dormant leaf buds against frost damage, dehydration, and insect herbivory. Bud resins contain a wide variety of special metabolites including terpenoids, benzenoids, and phenolics. The leaf bud resins of Populus trichocarpa and P. balsamifera contain high concentrations of O-methylated dihydrochalcones, but the enzymes for methylating these compounds remain enigmatic. We used transcriptomics and differential gene expression analyses to identify a gene encoding a P. trichocarpa DHC-specific O-methyltransferase, which we named PtDOMT1. Detailed enzymatic analyses demonstrated PtDOMT1 to be a highly selective and regiospecific O-methyltransferase which methylates 4- and 4'-positions of dihydrochalcones using S-adenosyl-L-methionine as a methyl donor. PtDOMT1 did not methylate any other flavonoid or phenolic substrate tested. These findings establish the final step in the biosynthesis of O-methylated dihydrochalcones in poplar and represent the first molecular analysis of leaf bud resin biosynthesis in plants.

Alternative oxidase (AOX) regulates the level of reactive oxygen species and nitric oxide (NO) in plants. While under normoxic conditions it alleviates NO formation, there are several indications that in the conditions of low oxygen such as during seed germination before radicle protrusion, in meristematic stem cells, and in flooded roots AOX can be involved in the production of NO from nitrite. Whereas the first reports considered this role as indirect, more evidence is accumulated that AOX can act as a nitrite: NO reductase. Such activity of the structurally similar di-iron proteins in bacteria has been demonstrated. We review the literature on this topic and show that AOX can be induced under hypoxic conditions and participate in NO turnover via the phytoglobin-NO cycle. This results in the facilitation of glycolytic reactions by reoxidation of the glycolytically formed NADH and diverting the glycolytic carbon toward the formation of alanine and other amino acids. Pyruvate formed in glycolysis can activate AOX and facilitate its operation under these conditions. It is concluded that AOX is an important player in the hypoxic response in plants that regulates the redox level by participating in NO turnover as a nitrite: NO reductase in cooperation with nitrate reductase and phytoglobin.

The flowering time of Chrysanthemum morifolium predominantly depends on day length but is also sensitive to ambient temperature. However, the mechanisms underlying the response of chrysanthemum to ambient temperature are mainly unknown. This study identified a MADS-box transcription factor called CmFLC-like, a representative low ambient temperature-responsive factor induced in chrysanthemum leaves and shoot apical meristems at 15°C. Subsequently, CmFLC-like localizes to the cell nucleus and membrane and functions as a transcriptional repressor. CmFLC-like overexpression made plants more sensitive to low-temperature-induced late flowering, whereas the chimeric activator CmFLC-like-VP64 was less sensitive at 15°C, indicating that CmFLC-like was involved in thermosensory flowering. Transcriptome profiling of CmFLC-like transgenic plants suggested that the potential target genes for low ambient temperature-responsive CmFLC-like regulation are predominantly flowering integrators, MADS-box transcription factors, and AP2 genes. Subsequent examination revealed that the orchestrated repression of CmAFL1 and CmFTL3 by CmFLC-like was mediated by its direct binding to the CArG-box element of their promoters. This study offers novel insights into the molecular mechanisms underlying chrysanthemum flowering and highlights the essential role of CmFLC-like proteins in the thermosensory pathway.

Plants commonly undergo leaf morphoanatomy and composition modifications to cope with drought stress, and these tend to reduce mesophyll conductance to CO2 diffusion (gm), a key limitation to photosynthesis. The cell wall appears to play a crucial role in this reduction, yet the specific effect of cell wall compositions on gm and the underlying regulatory mechanisms of cell wall thickness (Tcw) variation are not well understood. In this study, we subjected cotton plants to varying levels of water deficit to investigate the impact of leaf cell wall composition and the arrangement patterns of microfibrils within cell walls on Tcw and leaf gas exchange. Drought stress resulted in a significant thickening of cell walls and a decrease in gm. Concurrently, drought stress increased the content of chelator-soluble pectin and cellulose while reducing hemicellulose content. The alignment of cellulose microfibrils became more parallel and their diameter increased with under drought conditions, suggesting a decrease in cell wall effective porosity which coincides with the observed reduction in gm. This research demonstrates that reduced gm typically observed under drought stress conditions is related not only to thickened cell walls, but also to ultra-anatomical and compositional variations. Specifically, increases in cellulose content, diameter, and highly aligned arrangement collectively contributed to an increase in Tcw, which together with increases in chelator-soluble pectin content, resulted in an increased cell wall resistance to CO2 diffusion.

The phosphatidylethanolamine-binding protein (PEBP) family members FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1) are major regulators of plant reproduction. In Arabidopsis, the FT/TFL1 balance defines the timing of floral transition and the determination of inflorescence meristem identity. However, emerging studies have elucidated a plethora of previously unknown functions for these genes in various physiological processes. Here, we characterized potential roles in seed size and dormancy of FT and TFL1 in Arabidopsis thaliana using CRISPR mutants and reporter analysis. Our findings unveiled a role for TFL1 in seed dormancy while confirming the role of FT in regulating this trait. We showed that the interplay between these two genes in seed dormancy is antagonistic, mirroring their roles in flowering time and inflorescence architecture. Analysis of reporter lines demonstrated that FT and TFL1 are partly co-expressed in seeds. Finally, we showed that total seed yield is affected in these mutants. Together, our results highlight the versatility of these two genes beyond their canonical functions. The impact of FT and TFL1 on seed characteristics emphasizes the significance of approaching gene studies from various perspectives, enabling the identification of multifaceted molecular factors that could play a major role in shaping the future of agriculture.

Jasmonic acid (JA), ethylene (ET) and salicylic acid (SA) are the three major phytohormones coordinating plant defense responses, and all three are implicated in the defense against the fungal pathogen Fusarium oxysporum. However, their distinct modes of action and possible interactions remain unknown, in part because all spatial information on their activity is lacking. Here, we set out to probe this spatial aspect of plant immunity by using live-microscopy with newly developed fluorescence-based transcriptional reporter lines. We have created a GreenGate vector collection of Plant Immune system Promoters (GG-PIPs) that allow us to image local activation of immune pathways with single-cell resolution. Using this system, we demonstrate that SA and JA act spatially separate from each other in distinct sets of root cells neighboring the fungal colonization site, while ET contributes to both sets. SA & ET induce the hypersensitive response as a first line of defense, while JA & ET govern active defense against the pathogen in a separate, second line of defense. Such an approach to resolve the plant's immune responses on an individual cell level has been lacking, and this work demonstrates that this microscopy-based approach can contribute to understanding plant immune responses in detail.

Micronutrient malnutrition is one of the most serious health challenges facing vast sectors of Africa's population particularly resource-poor women and children. Main deficiencies include iron, zinc and vitamin A. Plant breeding has frequently been advocated as the most sustainable strategy of providing varieties of different food crop species with enhanced micronutrient density to combat the global hidden hunger problem which affects more than 2 billion people. However, there are few research programs which have implemented this approach from concept stage to finished products which can be widely disseminated and commercialised to create meaningful impact. The East African bean biofortification program offers a case study of such a program. The aim of this program was to develop well adapted, high yielding, Fe and Zn rich bush and climbing bean cultivars and agronomic approaches that enhance expression of high mineral trait. The objective of this review is to provide a synthesis of the progress made in the last 22 years, with a focus on genetic diversity, inheritance and bioavailability of Fe and Zn, cooking quality, and to identify research gaps and suggest future directions.

Phenotypic plasticity can contribute to crop adaptation to challenging environments. Plasticity indices are potentially useful to identify the genetic basis of crop phenotypic plasticity. Numerous methods exist to measure phenotypic plasticity. However, their ability to capture QTL with environmental effects remains elusive. Here, we analyzed a published multi-trial maize phenotyping dataset that examined the water stress response of leaf area, shoot biomass and water use efficiency, calculating phenotypic plasticity for these traits using seven different plasticity indices. A comprehensive genetic analysis of phenotypic plasticity for these traits was further performed and the ability of these methods to detect genetic regions capturing variance due to genotype-by-environment (G x E) interaction was evaluated. Our results suggest that not all plasticity indices are amenable to identify genomic regions associated with phenotypic plasticity. We observed that plasticity indices based on calculation of a ratio between environments or the slope of the Finlay-Wilkinson model were particularly useful in uncovering the genetic architecture underlying phenotypic plasticity when studying responses to treatments within and across trials. Ultimately, a deeper understanding of phenotypic plasticity should provide opportunities for breeding plants better able to adapt to climate uncertainty.

Complex N-glycans are asparagine (N)-linked branched sugar chains attached to secretory proteins in eukaryotes. They are produced by modification of N-linked oligosaccharide structures in the endoplasmic reticulum (ER) and Golgi apparatus. Complex N-glycans formed in the Golgi apparatus are often assigned specific roles unique to the host organism, with their roles in plants remaining largely unknown. Using inhibitor (kifunensine, KIF)-hypersensitivity as read-out, we identified Arabidopsis mutants that require complex N-glycan modification. Among over 100 KIF-sensitive mutants, one showing abnormal secretory organelles and a salt-sensitive phenotype contained a point mutation leading to amino-acid replacement (G69R) in ARFA1E, a small Arf1-GTPase family protein presumably involved in vesicular transport. In-vitro assays showed that the G69R exchange interferes with protein activation. In vivo, ARFA1EG69R caused dominant-negative effects, altering the morphology of the ER, Golgi apparatus, and trans-Golgi network (TGN). Post-Golgi transports (endocytosis/endocytic recycling) of essential glycoprotein KORRIGAN1, one of KIF-sensitivity targets, is slowed down constitutively as well as under salt stress in ARFA1EG69R mutant. Because regulated cycling of plasma membrane proteins is required for stress tolerance of the host plants, ARFA1EG69R mutant established a link between KIF-targeted luminal glycoprotein functions/dynamics and cytosolic regulators of vesicle transport in endosome-/cell wall-associated tolerance mechanisms.

Several plant seeds release a mucilaginous envelope through hydration, rich in pectins and stabilized by cellulose fibers. This mucilage aids in seed protection, development, and adhesion for dispersal. This study aimed to separate the effects of pectins and cellulose fibers by using pectinase to remove mucilage pectins, leaving cellulose arrays, and performing wet and dry pull-off force measurements on seeds of three plant species: Salvia hispanica (Chia), Collomia grandiflora (Collomia) and Linum usitatissimum (Flax). We used light and scanning electron microscopy to confirm partial pectin removal and intact cellulose fibers. Pull-off force measurements revealed similar wet adhesive properties and E-moduli in S. hispanica and C. grandiflora seeds before and after pectin removal. L. usitatissimum seeds, lacking cellulose fibers, exhibited significantly lower wet and dry adhesion forces post-pectin removal. Desiccation dynamics showed shorter desiccation times after pectin removal in all three species. Results indicated that adhesion forces in seed mucilage with cellulose fibers did not change significantly after pectin removal, suggesting that cellulose fibers contribute to the adhesive properties of seed mucilage, while pectins might not play an exclusive role in adhering to surfaces.