Journal of Experimental Botany

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ISSN / EISSN : 0022-0957 / 1460-2431
Published by: Oxford University Press (OUP) (10.1093)
Total articles ≅ 17,098
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Samuel Gámez-Arcas, Edurne Baroja-Fernández, Pablo García-Gómez, Francisco José Muñoz, Goizeder Almagro, Abdellatif Bahaji, Ángela María Sánchez-López,
Journal of Experimental Botany; https://doi.org/10.1093/jxb/erab463

Abstract:
Microorganisms communicate with plants by exchanging chemical signals throughout the phytosphere. Before direct contact with plants occurs, beneficial microorganisms emit a plethora of volatile compounds (VCs) that promote plant growth and photosynthesis as well as developmental, metabolic, transcriptional and proteomic changes in plants. These compounds can also induce systemic drought tolerance and improve water and nutrient acquisition. Recent studies have shown that this capacity is not restricted to beneficial microbes; it also extends to phytopathogens. The response of plants to microbial VCs has frequently been associated with volatile organic compounds with molecular masses ranging between ca. 45 Da and 300 Da. However, microorganisms also release a limited number of VCs with molecular masses of less than ca. 45 Da that react with proteins and/or act as signaling molecules. Some of these compounds promote photosynthesis and growth when exogenously applied in low concentrations. Recently, evidence has been compiled that small VCs are important determinants of plant responses to microbial volatile emissions. However, the regulatory mechanisms involved in these responses remain poorly understood. This review summarizes the current knowledge about the biochemical and molecular mechanisms involved in the growth, developmental and metabolic responses of plants to small microbial VCs.
Geun Cheol Song, Je-Seung Jeon, Hee-Jung Sim, Soohyun Lee, Jihye Jung, Sang-Gyu Kim, Sun Young Moon,
Journal of Experimental Botany; https://doi.org/10.1093/jxb/erab466

Abstract:
Bacteria emit volatile compounds that modulate plant growth. Previous studies reported the impacts of bacterial volatile compounds on plant growth; however, the results varied depending on bacterial nutrient availability. We investigated whether the effects of plant growth–inhibiting volatiles (PGIVs) and plant growth–promoting volatiles (PGPVs) depended on the perceived dose by evaluating the growth of Arabidopsis thaliana seedlings placed at 7, 14, and 21 cm away from Bacillus amyloliquefaciens GB03 colonies growing in rich medium. A large bacterial colony (500 μL inoculum) inhibited plant growth at 7 cm and promoted growth at 21 cm, whereas a small bacterial colony (100 μL inoculum) induced the reverse outcomes. We identified pyrazine and 2,5-dimethylpyrazine as candidate PGIVs that significantly reduced plant growth at 7 cm distance. PGIV effects were validated by exposing plants to synthetic 2,5-dimethylpyrazine and bacteria emitting PGPVs, which showed that PGIVs overwhelm PGPVs to rapidly increase salicylic acid levels and related gene expression pathways. This is referred to as the defense-growth trade-off. Our results indicate that high PGIV concentrations suppress growth and promote plant immunity, whereas low PGPV concentrations promote growth. This study provides novel insights into the complex effects of bacterial volatile mixtures and fine-tuning of bacteria-plant interactions.
Anh H Ngo, Artik Elisa Angkawijaya, Ying-Chen Lin, Yu-Chi Liu, Yuki Nakamura
Journal of Experimental Botany; https://doi.org/10.1093/jxb/erab436

Abstract:
Phosphorus (P) is an essential nutrient for plants. Membrane lipid remodeling is an adaptive mechanism for P-starved plants that replaces membrane phospholipids with non-P galactolipids, presumably to retrieve scarce P sources and maintain membrane integrity. Whereas metabolic pathways to convert phospholipids to galactolipids are well-established, the mechanism by which phospholipid biosynthesis is involved in this process remains elusive. Here, we report that phospho-base N-methyltransferases 1 and 2 (PMT1 and PMT2), which convert phosphoethanolamine to phosphocholine (PCho), are transcriptionally induced by P starvation. Shoots of seedlings of pmt1 pmt2 double mutant showed defective growth upon P starvation; however, membrane lipid profiles were unaffected. We found that P-starved pmt1 pmt2 with defective leaf growth had reduced PCho content, and the growth defect was rescued by exogenous supplementation of PCho. We propose that PMT1 and PMT2 are induced by P starvation to produce PCho mainly for leaf growth maintenance, rather than for phosphatidylcholine biosynthesis, in membrane lipid remodeling.
Maketalena Aleamotu’A, Jaime K Baker, ,
Journal of Experimental Botany; https://doi.org/10.1093/jxb/erab468

Abstract:
Phi thickenings are peculiar secondary cell wall thickenings found in radial walls of cortical cells in plant roots. However, while thickenings are widespread in the plant kingdom, research into their development has been lacking. Here, we describe a simple system for rapid induction of phi thickenings in primary roots of Brassica. Four-day old seedlings were transferred from control agar plates to new plates containing increased levels of osmotica. Phi thickening development occurred within a narrow region of the differentiation zone proportional to osmolarity, with cellulose deposition and lignification starting after twelve and fifteen hours respectively. However, osmoprotectants not only failed to induce phi thickenings, but inhibited induction when tested in combination with thickening-inducing osmotica. An independent, biomechanical pathway exists regulating phi thickening induction, with root growth rates and substrate texture being important factors in determining thickening induction. Phi thickening development is also controlled by stress-related plant hormones, most notably jasmonic acid but also abscisic acid. Our research not only provides the first understanding of the developmental pathways controlling phi thickening induction, but provides tools with which the functions of these enigmatic structures might be clarified.
, Stefanie Schmier, Holger F Bohn, Svenja Kleiser, ,
Journal of Experimental Botany; https://doi.org/10.1093/jxb/erab456

Abstract:
The climbing passionflower Passiflora discophora features branched tendrils with multiple adhesive pads at their tips allowing it to attach to large diameter supports and to flat surfaces. We conducted tensile tests to quantify the performance of this attachment system. We found that the force at failure varies with substrate, ontogenetic state (turgescent, senescent), and tendril size (i.e., tendril cross-sectional area and pad area). The tendrils proved to be well balanced in size and to attach firmly to a variety of substrates (force at failure up to 2 N). Pull-off tests performed with tendrils grown on either epoxy, plywood, or beech bark revealed that senescent tendrils could still bear 24%, 64%, or 100% of the force measured for turgescent tendrils, respectively, thus providing long-lasting attachment at minimal physiological costs. The tendril main axis was typically the weakest part of the adhesive system, whereas the pad-substrate interface never failed. This suggests that the plants use the slight oversizing of adhesive pads as a strategy to cope with “unpredictable” substrates. The pads, together with the spring-like main axis, which can, as shown, dissipate a large amount of energy when straightened, thus constitute a fail-safe attachment system.
Declan J Lafferty, Richard V Espley, Cecilia H Deng, Catrin S Günther, Blue Plunkett, Janice L Turner, Laura Jaakola, Katja Karppinen, Andrew C Allan,
Journal of Experimental Botany; https://doi.org/10.1093/jxb/erab460

Abstract:
Members of the Vaccinium genus bear fruits rich in anthocyanins, a class of red-purple flavonoid pigments that provide human health benefits, although the localization and concentrations of anthocyanins differ between species: blueberry (V. corymbosum) has white flesh, while bilberry (V. myrtillus) has red flesh. Comparative transcriptomics between blueberry and bilberry revealed that MYBPA1.1 and MYBA1 strongly correlated with the presence of anthocyanins, but were absent or weakly expressed in blueberry flesh. MYBPA1.1 had a biphasic expression profile, correlating with both proanthocyanidin biosynthesis early during fruit development and anthocyanin biosynthesis during berry ripening. MYBPA1.1 was unable to induce anthocyanin or proanthocyanidin accumulation in Nicotiana benthamiana, but activated promoters of flavonoid biosynthesis genes. The MYBPA1.1 promoter is directly activated by MYBA1 and MYBPA2 proteins, which regulate anthocyanins and proanthocyanidins, respectively. Our findings suggest the lack of VcMYBA1 expression in blueberry flesh results in an absence of VcMYBPA1.1 expression, which are both required for anthocyanin regulation. In contrast, VmMYBA1 is well-expressed in bilberry flesh, upregulating VmMYBPA1.1, allowing coordinated regulation of flavonoid biosynthesis genes and anthocyanin accumulation. The hierarchal model described here for Vaccinium may also occur in a wider group of plants as a means to co-regulate different branches of the flavonoid pathway.
Jitka Ortmannová, Juraj Sekereš, Ivan Kulich, Jiří Šantrůček, Petre Dobrev, Viktor Žárský,
Journal of Experimental Botany; https://doi.org/10.1093/jxb/erab457

Abstract:
In the reaction to non-adapted Blumeria graminis f. sp. hordei (Bgh), Arabidopsis thaliana leaf epidermal cells deposit cell wall reinforcements called papillae or seal fungal haustoria in encasements, both of which involve intensive exocytosis. A plant syntaxin SYP121/PEN1 has been found to be of key importance for the timely formation of papillae, and the vesicle tethering complex exocyst subunit EXO70B2 has been found to contribute to their morphology. Here, we identify a specific role for the EXO70B2-containing exocyst complex in the papillae membrane domains important for the callose deposition and GFP-SYP121 delivery to the focal attack sites, as well as its contribution to encasement formation. The mRuby2-EXO70B2 co-localises with the exocyst core subunit SEC6 and GFP-SYP121 in the membrane domain of papillae, and EXO70B2 and SYP121 proteins have the capacity to directly interact. The exo70B2/syp121 double mutant has a reduced number of papillae and haustorial encasements in response to Bgh, indicating an additive role of the exocyst in SYP121 coordinated non-host resistance. In summary, we report cooperation between the plant exocyst and a SNARE protein in penetration resistance against non-adapted fungal pathogens.
Sophie B Cowling, Pracha Treeintong, John Ferguson, Hamidreza Soltani, , ,
Journal of Experimental Botany; https://doi.org/10.1093/jxb/erab459

Abstract:
African rice (Oryza glaberrima) has adapted to challenging environments and is a promising source of genetic variation. We analysed dynamics of photosynthesis and morphology in a reference set of 155 O. glaberrima accessions. Plants were grown in an agronomy glasshouse to late tillering stage. Photosynthesis induction from darkness and the decrease in low light was measured by gas exchange and chlorophyll fluorescence along with root and shoot biomass, stomatal density and leaf area. Steady state and kinetic responses were modelled. We describe extensive natural variation in O. glaberrima for steady state, induction and reduction responses of photosynthesis that has value for gene discovery and crop improvement. Principle component analyses indicated key clusters of plant biomass, kinetics of photosynthesis (CO2 assimilation, A) and photoprotection induction and reduction (measured by Non Photochemical Quenching, NPQ), consistent with diverse adaptation. Accessions also clustered according to countries with differing water availability, stomatal conductance (gs), A and NPQ and indicating that dynamic photosynthesis has adaptive value in O.glaberrima. Kinetics of NPQ, A and gs showed high correlation with biomass and leaf area. We conclude that dynamic photosynthetic traits and NPQ are important within O.glaberrima and we highlight NPQ kinetics and NPQ under low light.
Emma K Turley,
Journal of Experimental Botany; https://doi.org/10.1093/jxb/erab455

Abstract:
The development of secondary vascular tissue enhances the transport capacity and mechanical strength of plant bodies, while contributing a huge proportion of the world’s biomass in the form of wood. Cell divisions in the cambium, which constitutes the vascular meristem, provide progenitors from which conductive xylem and phloem are derived. The cambium is a somewhat unusual stem cell population in two respects, making it an interesting subject for developmental research. Firstly, it arises post-germination, and thus represents a model for understanding stem cell initiation beyond embryogenesis. Secondly, xylem and phloem differentiate on opposing sides of cambial stem cells, making them bifacial in nature. Recent discoveries in Arabidopsis thaliana have provided insight into the molecular mechanisms that regulate the initiation, patterning, and maintenance of the cambium. In this review, the roles of intercellular signalling via mobile transcription factors, peptide-receptor modules and phytohormones are described. Cross-talk between these regulatory pathways is becoming increasingly apparent, yet the underlying mechanisms are not fully understood. Future study of the interaction between multiple independently identified regulators, as well as the functions of their orthologs in trees, is needed to deepen our understanding of radial growth in plants.
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