Journal of Experimental Botany最新文献

An approach to improving radiation use efficiency (RUE) in wheat is to screen for variability in rates of leaf respiration in darkness (Rdark). We used a high-throughput system to quantify variation in Rdark among a diverse range of spring wheat genotypes (301 lines) grown in two countries (Mexico and Australia) and two seasons (2017 and 2018), and in doing so quantify the relative importance of genotype (G) and environment (E) in influencing variations in leaf Rdark. Through careful design, residual (unexplained) variation represented <10% of the total observed. Up to a third of the variation in Rdark (and related traits) was under genetic control. This suggests opportunities for breeders to use Rdark as a novel selection tool. In addition, E accounted for more than half of the total variation in area-based rates of Rdark. Here, the day of measurement was crucial, suggesting that day-to-day variations in the environment influence rates of Rdark measured at a common temperature. Overall, this study provides new insights into the role G and E play in determining variation in rates of leaf Rdark of one of the most important cereal crops, with implications for future improvements in carbon use efficiency and yield.

Frankia cluster-2 strains are diazotrophs that engage in root nodule symbiosis with actinorhizal plants of the Cucurbitales and the Rosales. Previous studies have shown that an assimilated nitrogen source, presumably arginine, is exported to the host in nodules of Datisca glomerata (Cucurbitales), while a different metabolite is exported in the nodules of Ceanothus thyrsiflorus (Rosales). To investigate if an assimilated nitrogen form is commonly exported to the host by cluster-2 strains, and which metabolite would be exported in Ceanothus, we analysed gene expression levels, metabolite profiles, and enzyme activities in nodules. We conclude that the export of assimilated nitrogen in symbiosis seems to be a common feature for Frankia cluster-2 strains, but the source of nitrogen is host dependent. The export of assimilated ammonium to the host suggests that 2-oxoglutarate is drawn from the tricarboxylic acid (TCA) cycle at a high rate. This specialized metabolism obviates the need for the reductive branch of the TCA cycle. We found that several genes encoding enzymes of central carbon and nitrogen metabolism were lacking in Frankia cluster-2 genomes: the glyoxylate shunt and succinate semialdehyde dehydrogenase. This led to a linearization of the TCA cycle, and we hypothesized that this could explain the low saprotrophic potential of Frankia cluster-2.

The need to address the impact of domestication on plant traits is frequently highlighted in modern agriculture. It is often argued that domesticated plants have lost competitive ability due to reduced phenotypic plasticity. This study investigates whether domestication has affected competitive ability, functional trait values, and plasticity in durum wheat across 39 genotypes representing four key stages of domestication, from wild progenitors to modern elite varieties. Plants were grown in pots, both alone and in competition with the same neighbouring genotype. Biomass, and above- and belowground traits were measured at the end of the vegetative stage. Our results showed that the three domesticated groups lost less biomass in response to competition compared with their wild progenitors. All genotypes developed thinner leaves and thicker roots when grown with a neighbour. While wild progenitors exhibited the highest plasticity, this did not translate to a greater competitive ability. These findings challenge the theoretical expectation that domesticated plants are less suited for competition. Instead, they suggest that domesticated plants perform well in competitive environments and question the need to reintroduce wild traits to improve competitive ability.

Lipid transfer proteins (LTPs) are small cysteine-rich soluble proteins that affect flower and seed development, cuticular wax deposition, and biotic and abiotic stress responses. We isolated an LTP-encoding gene homologous to LTPVAS in Nicotiana benthamiana and designated it LTP-VASCULAR TISSUE SIZE (NbLTPVAS). This gene was expressed in seeds, leaves, roots, and stems. Additionally, NbLTPVAS expression was induced by hypersensitive response (HR)-inducing agents. Cell death was accelerated and the phytopathogenic bacterial population decreased significantly in NbLTPVAS-silenced plants infected with the incompatible Ralstonia solanacearum strain 8107. The expression of HR marker gene hin1 in NbLTPVAS-silenced plants was markedly induced by R. solanacearum 8107, indicative of the acceleration of HR. HR cell death in NbLTPVAS-silenced plants was also promoted by the Agrobacterium-mediated expression of HR-inducing proteins including INF1, AvrA, and PopP1. Excessive production of reactive oxygen species (ROS) was detected in NbLTPVAS-silenced plants. The expression of NbrbohB (encoding a ROS-generating enzyme) also increased in NbLTPVAS-silenced plants, but the expression of the antioxidant enzyme-encoding genes NbSOD and NbAPX decreased. The silencing of both NbLTPVAS and NbrbohB adversely affected HR induction. Moreover, NbLTPVAS was secreted into the intercellular washing fluid. The transient expression of the full-length NbLTPVAS induced the expression of antioxidant genes, attenuated ROS production, and suppressed the induction of HR cell death. This is the first functional analysis of LTPVAS in plant-microbe interactions. Our study provides novel insights into the role of NbLTPVAS as a negative regulator of HR via ROS homeostasis in N. benthamiana.

Rising winter temperatures jeopardize the fruit yield of trees that require a prolonged and sufficiently cold winter to flower. Predicting the exact risk to different crop varieties is the first step in mitigating the harmful effects of climate change. This work focused on olive (Olea europaea)-a traditional crop in the Mediterranean basin in which flowering depends on the sufficiency of cold periods and the lack of warm ones during the preceding winter. A satisfactory quantitative model forecasting its expected flowering under natural temperature conditions is still lacking. The effect of different temperature regimes on olive flowering level and flowering gene expression was tested empirically. A modified 'dynamic model' describing the response of a putative flowering factor to the temperature signal was constructed. The crucial component of the model was an unstable intermediate, produced and degraded at temperature-dependent rates. The model accounts for the number of both cold and warm hours and also for their sequence. Empirical flowering and temperature data were applied to fit the model parameters, using numerical constrained optimization techniques; the model outcomes were successfully validated. The model accurately predicted low-to-moderate flowering under winters with warm periods and properly accounted for the effects of warm periods during winter.

Cause-and-effect arrows are drawn from genotype (G), environment (E), and agronomic management (M) to the plant phenotype in crop stands in a useful but incomplete framework that informs research questions, experimental design, statistical analysis, data interpretation, modelling, and breeding and agronomic applications. Here we focus on the overlooked bidirectionality of these arrows. The phenotype-to-genotype arrow includes increased mutation rates in stressed phenotypes, relative to basal rates. From a developmental viewpoint, the phenotype modulates gene expression, returning multiple cellular phenotypes with a common genome. The phenotype-to-environment arrow is captured in the process of niche construction, which spans from persistent and global to transient and local. Research on crop rotations recognizes the influence of the phenotype on the environment but is divorced from niche construction theory. The phenotype-to-management arrow involves, for example, a diseased crop that may trigger fungicide treatment. Making explicit the bidirectionality of the arrows in the G×E×M framework contributes to narrowing the gap between data-driven technologies and integrative theory, and is an invitation to think cautiously of the internal teleonomy of plants in contrast to the view of the phenotype as the passive end of the arrows in the current framework.

The extensive use of nitrogen fertilizers has detrimental environmental consequences, and it is essential for society to explore sustainable alternatives. One promising avenue is engineering root nodule symbiosis, a naturally occurring process in certain plant species within the nitrogen-fixing clade, into non-leguminous crops. Advancements in single-cell transcriptomics provide unprecedented opportunities to dissect the molecular mechanisms underlying root nodule symbiosis at the cellular level. This review summarizes key findings from single-cell studies in Medicago truncatula, Lotus japonicus, and Glycine max. We highlight how these studies address fundamental questions about the development of root nodule symbiosis, including the following findings: (i) single-cell transcriptomics has revealed a conserved transcriptional program in root hair and cortical cells during rhizobial infection, suggesting a common infection pathway across legume species; (ii) characterization of determinate and indeterminate nodules using single-cell technologies supports the compartmentalization of nitrogen fixation, assimilation, and transport into distinct cell populations; (iii) single-cell transcriptomics data have enabled the identification of novel root nodule symbiosis genes and provided new approaches for prioritizing candidate genes for functional characterization; and (iv) trajectory inference and RNA velocity analyses of single-cell transcriptomics data have allowed the reconstruction of cellular lineages and dynamic transcriptional states during root nodule symbiosis.

Sterols are produced via complex, multistep biosynthetic pathways involving similar enzymatic conversions in plants, animals, and fungi, yielding a variety of sterol metabolites with slightly different chemical properties to exert diverse and specific functions. A tremendously diverse landscape of sterols, and sterol-derived compounds can be found across the plant kingdom, determining a wide spectrum of functions. Resolving the underlying biosynthetic pathways is thus instrumental to understanding the function and use of these molecules. In only a few plants, sterol biosynthesis has been studied using mutants. In non-model species, a pharmacological approach is required. However, this relies on only a few inhibitors. Here, we investigated a collection of inhibitors of mammalian cholesterol biosynthesis to identify new inhibitors of plant sterol biosynthesis. We showed that imidazole-type fungicides, bifonazole, clotrimazole, and econazole, inhibited the obtusifoliol 14α-demethylase CYP51 in plants. Moreover, we found that the selective estrogen receptor modulator, clomiphene, inhibited sterol biosynthesis in part by inhibiting the plant-specific cyclopropyl-cycloisomerase CPI1. These results demonstrate that rescreening of inhibitors of animal sterol biosynthesis is an easy approach for identifying novel inhibitors of plant sterol biosynthesis. The molecules used in this study expand the range of inhibitors for studying and manipulating sterol biosynthesis in the plant kingdom.

Plant growth depends on growth regulators, nutrient availability, and amino acid levels, all of which influence cell wall formation and cell expansion. Cell wall integrity and structures are surveyed and modified by a complex array of cell wall integrity sensors, including leucine-rich repeat (LRR)-extensins (LRXs) that bind RALF (rapid alkalinization factor) peptides with high affinity and help to compact cell walls. Expressing the Arabidopsis root hair-specific LRX1 without the extensin domain, which anchors the protein to the cell wall (LRX1ΔE14), has a negative effect on root hair development. The mechanism of this negative effect was investigated by a suppressor screen, which led to the identification of a sune (suppressor of dominant-negative LRX1ΔE14) mutant collection. The sune82 mutant was identified as an allele of HISN2, which encodes an enzyme essential for histidine biosynthesis. This mutation leads to reduced accumulation of histidine and an increase in several amino acids, which appears to have an effect on the TOR (target of rapamycin) network, a major controller of eukaryotic cell growth. It also represents an excellent tool to study the effects of reduced histidine levels on plant development, as it is a rare example of a viable partial loss-of-function allele in an essential biosynthetic pathway.