Journal of Experimental Botany
ISSN / EISSN : 0022-0957 / 1460-2431
Published by: Oxford University Press (OUP) (10.1093)
Total articles ≅ 16,977
Latest articles in this journal
Journal of Experimental Botany; doi:10.1093/jxb/erab328
Sharp eyespot, caused by the necrotrophic fungal pathogen Rhizoctonia cerealis, is a devastating disease of bread wheat (Triticum aestivum). However, the molecular mechanisms underlying wheat defense against Rhizoctonia cerealis are still largely unknown. In this study, we identified a novel cysteine-rich receptor-like kinase (CRK)-encoding gene, designated as TaCRK3, through comparative transcriptomic analysis, and investigated its defence role against Rhizoctonia cerealis. TaCRK3 transcriptional abundance was significantly elevated by R. cerealis and exogenous ethylene treatments. Silencing of TaCRK3 significantly compromised resistance to R. cerealis and repressed expression of an ethylene biosynthesis enzyme-encoding gene ACO2 and a subset of defence-associated genes in wheat, whose transcript levels are up-regulated by ethylene stimulus. TaCRK3 protein was localized at the plasma membrane in wheat. Noticeably, both the heterologously-expressing TaCRK3 protein and its partial peptide harboring two DUF26 domains could inhibit growth of R. cerealis mycelia. These results suggest that the TaCRK3 mediates wheat resistance to R. cerealis through direct-antifungal activity and heightening the expression of defence-associated genes in the ethylene signaling pathway, and that its DUF26 domains are required for the antifungal activity of TaCRK3. This study provides a promising gene for breeding wheat varieties with resistance to R. cerealis.
Journal of Experimental Botany; doi:10.1093/jxb/erab325
Although autocatalytic ethylene biosynthesis plays an important role in the ripening of climacteric fruits, our knowledge of the network that promotes autocatalytic ethylene biosynthesis remains limited. We identified white fruit (wf), a tomato mutant that produces immature fruit that are white and that ripen slowly. We found that an inversion on chromosome 10 that disrupts the LUTESCENT2 gene, and the white fruit is allelic to lutescent 2. Using CRISPR-Cas9 technology we knocked out L2 in wild type tomato and found that the l2-cr mutants produced phenotype that were very similar to white fruit (lutescent 2). In the l2-cr fruit, chloroplast development was impaired and the accumulation of carotenoids and lycopene occurred more slowly than in wild type. During fruit ripening in l2-cr mutants, the peak of ethylene release was delayed, less ethylene was produced and the expression of ACO genes was significantly suppressed. We also found that exogenous ethylene induces the expression of L2 and that ERF.B3, an ethylene response factor, binds the promoter of the L2 gene and activates its transcription. Thus, the expression of L2 is regulated by exogenous ethylene. Taken together, our results indicate that ethylene may affect the expression of the L2 gene and that the L2 gene participates in autocatalytic ethylene biosynthesis during tomato fruit ripening.
Journal of Experimental Botany; doi:10.1093/jxb/erab329
Rice (Oryza sativa L.) is able to accumulate high Mn in the shoots through uptake by the roots, which consist of crown roots, lateral roots and root hairs. Here, we investigated the role of lateral roots and root hairs in Mn/Cd uptake by using two indica rice mutants defective in formation of lateral roots (osiaa11) and root hairs (osrhl1). When two mutants and their wild type (WT, cv. Kasalath) were grown hydroponically, the uptake of Mn and Cd in osiaa11 was significantly lower than that in WT, but there was no difference between WT and osrhl1. The lower Mn and Cd accumulation in the shoots of osiaa11 was also observed in plants grown in soils. Furthermore, a kinetic study showed that Mn uptake in osiaa11 was much lower than that in WT and osrhl1 in a wide range of Mn from 0.5 µM to 200 µM. The role of lateral roots in Mn and Cd uptake was further confirmed in a japonica rice mutant defective in lateral root formation. Comparison of gene expression of OsNramp5 and OsMTP9 involved in Mn uptake showed that the expression level of OsNramp5 but not OsMTP9 was lower in osiaa11 than WT, but was similar between osrhl1 and WT. Immunostaining showed that OsNramp5 and OsMTP9 were localized in the exodermis and endodermis of crown roots and lateral roots, but not in epidermis/root hairs. Taken together, our results indicate that lateral roots but not root hairs play an important role in high Mn and Cd uptake.
Journal of Experimental Botany; doi:10.1093/jxb/erab326
To maximise the grain yield of spring wheat, flowering needs to coincide with the optimal flowering period (OFP) by minimising frost and heat stress on reproductive development. This global study conducted a comprehensive modelling analysis of genotype, environment and management to identify the OFPs for sites in irrigated mega-environments (MEs) of spring wheat where the crop matures during a period of increasing temperatures. We used a gene-based phenology model to conduct long-term simulation analysis with parameterised genotypes to identify OFPs and optimal sowing dates for sites in irrigated MEs, considering the impacts of frost and heat stress on yield. The validation results showed that the gene-based model accurately predicted wheat heading dates across global wheat environments. The long-term simulations indicated that frost and heat stress significantly advanced or delayed OFPs and shrank the durations of OFPs in irrigated MEs when compared to OFPs where the model excluded frost and heat stress impacts. The simulation results (incorporating frost and heat penalties on yield) also showed that earlier flowering generally resulted in higher yields, and early sowing dates and/or early flowering genotypes were suggested to achieve early flowering. These results provided an interpretation of the regulation of wheat flowering to OFP by the selection of sowing date and cultivar to achieve higher yields in irrigated MEs.
Published: 9 July 2021
Journal of Experimental Botany; doi:10.1093/jxb/erab322
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Journal of Experimental Botany; doi:10.1093/jxb/erab321
The plant vacuole recycles proteins and RNA delivered to it by autophagy. Here, we provide a comprehensive characterization of the plant vacuolar RNAome by isolating intact vacuoles from Arabidopsis plants, subsequent RNA purification and deep sequencing. In the vacuolar RNAomes, we detected ribosomal RNAs, and transfer RNAs, including those of chloroplast origin and small RNA types in addition. As autophagy is a main mechanism for the transport of RNA to the vacuole, atg5-1 mutants deficient in autophagy were included in our analysis. We observed severely reduced amounts of most chloroplast-derived RNA species in these mutants. By comparison with the cellular RNA composition, indications for the upregulation of alternative RNA breakdown pathways were obtained. By contrast, vacuolar RNA processing and composition in plants lacking vacuolar ribonuclease 2, involved in cellular RNA homeostasis, only showed minor alterations, possibly because of the presence of further so far unknown vacuolar RNase species. Among the small RNA types, we detected mature miRNAs in all vacuolar preparations but at much lower frequency in atg5-1, raising the possibility of a biological role for vacuolar miRNAs.
Published: 8 July 2021
Journal of Experimental Botany; doi:10.1093/jxb/erab323
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Journal of Experimental Botany; doi:10.1093/jxb/erab320
Mesophyll conductance (gm) is an important factor limiting photosynthesis. However, gm response to long-term growth in variable [CO2] is not well understood, particularly in crop plants. Here, we grew two cultivars of wheat (Halberd and Cranbrook), known to differ in gm under current environmental conditions, in four [CO2] treatments: glacial (206 μmol mol -1), pre-industrial (344 μmol mol -1), current ambient (489 μmol mol -1) and super-elevated (1085 μmol mol -1), and two water treatments (well-watered and moderate water limitation), to develop an evolutionary and future climate perspective on gm control of photosynthesis and water use efficiency (WUE). In the two wheat genotypes, gm increased with rising [CO2]from glacial to ambient [CO2], but declined at super-elevated [CO2]. The responses of gm to different growth [CO2]also depend on water stress; however, the specific mechanism of gm response to [CO2]remains unclear. Although gm and gm/gsc (mesophyll conductance/stomatal conductance) were strongly associated with the variability of photosynthetic rates (A) and WUE, we found that plants with higher gm may increase A without increasing gsc, which increased WUE. These results may be useful to inform plant breeding programs and cultivar selection for Australian wheat under future environmental conditions.
Journal of Experimental Botany; doi:10.1093/jxb/erab317
Plants ability to acquire soil N sources is plastic in response to abiotic and biotic factors. However, information about how plants N form preference changes in response to internal plant N demand, as through growth phases or to environmental stress as ozone (O3), is scarce. Diploid and triploid Chinese white poplar were used to investigate N form preferences at two key developmental moments (spring, summer) and in response to summer O3 (ambient, 60 ppb above ambient). We used stable isotopes to quantify NH4 +, NO3 - and glycine N-uptake rates. Carbon acquisition was recorded simultaneously. Both ploidy levels differed in growth, N form preferences, and N and C use strategy. Diploid grew faster in spring but slower in summer than triploid. Diploid showed plasticity among N forms through season, with no preferences in spring and NO3 - preferred in summer, while triploid showed an overall preference for NO3 -. Carbon acquisition and NO3 - uptake were inhibited in both ploidy levels at elevated O3, which also reduced diploid total N uptake. However, triploid alleviated N uptake reduction switching to similar preferences among N forms. Nitrogen form preferences are driven by internal C and N use in response to nutrient demands and external factors as O3.
Journal of Experimental Botany; doi:10.1093/jxb/erab316
Within the plant and earth sciences, stable isotope analysis is a versatile tool conveying information (inter alia) about plant physiological and paleoclimate variability across scales. Here, we identify a 13C signal (i.e., systematic 13C/ 12C variation) at tree-ring glucose C-4 and report an experimentally testable theory on its origin. We propose the signal is introduced by glyceraldehyde-3-phosphate dehydrogenases in the cytosol of leaves. It conveys two kinds of (potentially convoluted) information: (i) commitment of glyceraldehyde 3-phosphate to 3-phosphoglycerate vs. fructose 1,6-bisphosphate metabolism, and (ii) the contribution of non-phosphorylating vs. phosphorylating glyceraldehyde-3-phosphate dehydrogenase to catalysing the glyceraldehyde 3-phosphate to 3-phosphoglycerate forward reaction of glycolysis. Theory is supported by 13C fractionation modelling. Modelling results provide first evidence in support of the cytosolic oxidation-reduction (COR) cycle, a carbon-neutral mechanism supplying NADPH at the expense of ATP and NADH which may help to maintain leaf-cytosolic redox balances. In line with expectations related to COR cycling, we found a positive correlation between air vapour pressure deficit and 13C discrimination at glucose C-4. Overall, 13C-4 signal analysis may enable an improved understanding of leaf carbon and energy metabolism.