Journal of Experimental Botany最新文献

Crassulacean acid metabolism (CAM) plants primarily fix atmospheric CO2 at night and store it as malic acid in their vacuoles. During daytime, the vacuolar malate is remobilised and decarboxylated to supply CO2 for Rubisco assimilation. Light intensity and photoperiod play crucial roles in regulating this process, but their influences on the underlying molecular and biochemical mechanisms remain unclear. In this study, physiological, biochemical, and molecular approaches were integrated to uncover the temporal patterns and light responsiveness of gene transcript and protein abundances, and the activities of enzymes involved in diurnal malate remobilisation in the obligate CAM plant Kalanchoë fedtschenkoi. Vacuolar malate transport was primarily influenced by the endogenous clock and photoperiod, with the ALUMINIUM-ACTIVATED MALATE TRANSPORTER 4 (ALMT4) being a more plausible transporter candidate than the TONOPLAST DICARBOXYLATE TRANSPORTER (tDT). Malate decarboxylation was mainly dictated by photoperiod, with light intensity playing a supplementary role. Both photoperiod and light intensity greatly affected CO2 refixation and pyruvate recycling, with PYRUVATE ORTHOPHOSPHATE DIKINASE (PPDK) being the most strictly light-regulated player at the mRNA, protein abundance and activity levels, closely matching malate dynamics. Overall, PPDK seems to be a key regulator of light-dependent diurnal deacidification in CAM leaves, rather than the vacuolar malate transport or decarboxylation processes.

Tree height varies across environments, with taller individuals found in cool, moist habitats and shorter trees in drier regions. Within species, trees can exhibit height variation due to environmental factors such as drought-induced dieback. A key question is what drives changes in leaf structure with increasing height-whether some trait values cannot be produced under the developmental conditions at treetops or whether differences arise because natural selection favors particular trait values at different canopy positions. Some hypotheses suggest that increasing height imposes 'limits' on mature leaf traits, making some structural changes developmentally inevitable. However, selection could also favor structural changes within wide fields of developmentally possible trait configurations. We examined leaf epidermal cell size distributions in Bursera simaruba and Eucalyptus camaldulensis from seedlings to maximum tree heights in situations in which seedlings to adults were all exposed to full sun and thus had all 'sun' leaves. We found that in general cell sizes increased, variance remained high, and distributions did not systematically shift with height. These results indicate that, rather than reflecting a developmental inability to produce certain leaf epidermal cell sizes at greater heights, the patterns we observed are better explained by selection simply favoring some cell sizes from among the many that development can produce.

Tea gray blight disease represents a major fungal threat to tea plants, leading to substantial reductions in yield and declines in quality. It is prevalent in tea plantations globally. Given the considerable genetic diversity of pathogen populations across various tea-growing regions, understanding the population structure and pathogenic variation of dominant pathogens is essential for the development of sustainable ecological and economic management strategies. In this study, seven isolates of Pseudopestalotiopsis camelliae-sinensis, one of Pestalotiopsis camelliae, and one of Neopestalotiopsis sp. were identified from diseased leaves of Camellia sinensis 'Fudingdabai' in Shaanxi, China. Strain '10' demonstrated the highest pathogenicity and was identified as the primary pathogen responsible for gray blight. By assessing lesion area, leaf architecture, and biochemical constituents, the resistance levels of 20 tea cultivars were classified as highly resistant (one), resistant (four), intermediate resistant (eight), susceptible (five), and highly susceptible (two). Dynamic enzyme activity assays demonstrated a positive correlation between disease resistance in tea cultivars and the activities of peroxidase and phenylalanine ammonia-lyase, establishing a resistance hierarchy as follows: 'Longjingchangye'>'Zhongcha 108'>'Longjing 43'. Notably, cultivars exhibiting resistance showed significantly stabilized superoxide dismutase activity in comparison with susceptible genotypes. Cytological analyses of tea gray blight disease infection in highly resistant ('Longjingchangye'), highly susceptible ('Longjing 43'), and intermediate resistant ('Zhongcha 108') cultivars revealed a significantly reduced presence of appressoria and infection pegs in resistant genotypes relative to the susceptible cultivar. These findings provide a scientific foundation for the breeding of disease-resistant tea varieties and contribute to the understanding of plant-fungal pathogen interaction mechanisms.

The species Alternanthera philoxeroides is a flood-tolerant plant that has to cope with the hypoxic stress under submergence. However, the pith cavity in stems of this species is interrupted and partitioned by low-porosity diaphragms at the nodes. To date little knowledge is available about whether discontinuous pith cavities are functional for internal gas transport in plants. To disclose the role of stem discontinuous pith cavities in internal gas transport, the diffusive transport capacity of O2, the tissue O2 status of intact plants, and the influence of restricting longitudinal O2 supply on whole-plant growth during partial submergence were assessed. We found that stem pith cavities were the main pathway for diffusional supply of molecular O2; blocking only one internode significantly decreased the O2 flux to lower internodes, and the reduced O2 flux translated into reduced growth in partially submerged plants. A major output component of the study is a model that uses normalized tissue dimensions and concentration gradients to establish a fair foundation for comparison of contrasting species under different experimental conditions. We therefore predict that future studies will use this approach to further broaden the scope and value of resistance and flux measurement in target species.

Root system architecture affects water and mineral uptake and is important for plant adaptation to fluctuating nutrient availability. Small signaling peptides and their receptors influence root traits associated with macronutrient uptake. In this study, genome-wide association analyses were performed using 2D images of agar plate-grown Medicago truncatula accessions to understand the impact of GOLVEN10 peptide (GLV10) treatment on three root traits: root tortuosity, lateral root (LR) branch angle, and the gravity setpoint angle (GSA). Upon GLV10 treatment, roots of wild-type M. truncatula Jemalong A17 and R108 accessions showed increased primary root coiling (or tortuosity), increased LR branch angle, and reduced GSA. We identified 88 significant single nucleotide polymorphisms (SNPs) associated with these traits in GLV10-treated plants, distinct from the 163 SNPs in untreated plants. Importantly, the ethylene regulatory pathway was implicated in root tortuosity and LR emergence relative to the primary root. Application of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid reduced root sensitivity to GLV10, while the ethylene signaling mutant sickle was hypersensitive, indicating that GLV10 and ethylene pathways act antagonistically to control root tortuosity. These findings have implications for root gravitropic responses, and the ability of roots to penetrate deeper soil layers for nutrients and water.

Downy mildew, caused by Plasmopara viticola, is one of the most serious grapevine diseases. Resistant grapevines are a well-known tool for mitigating pathogen-caused damage. We evaluated 29 global grapevine cultivars from seven species for sensitivity to P. viticola. Chardonnay, belonging to the sensitive species Vitis vinifera, and Qingdahean, belonging to the well-known resistant species V. riparia, were chosen for further investigation into the resistance mechanism against downy mildew. Unlike Chardonnay, Qingdahean exerted an inhibitory effect on stomatal targeting, suppression of stomatal closure, stomatal penetration of P. viticola, and the development of primary hyphae and haustoria during the early phase of infection, and contained higher levels of malondialdehyde. Malondialdehyde was significantly increased by P. viticola infection, was toxic to the pathogen, and had an interfering effect on stomatal targeting. Furthermore, Qingdahean resisted pathogen invasion through the rapid induction of guard cell death and hypersensitive responses of other cell types. These findings suggest that resistance to P. viticola in V. riparia consists of layered stomatal immunity in addition to the well-known hypersensitive response, which is overcome by the pathogen in V. vinifera.

Plant callus cells possess a great capacity to regenerate organs or even whole plants. The mechanisms by which these cells maintain a proliferative state while retaining their pluripotent identity are poorly understood. By taking a multi-omics approach integrating epigenetic regulation (via chromatin immunoprecipitation and sequencing) with transcriptional output, we identify two complementary strategies that support callus cell pluripotency. First, callus cells prevent differentiation by promoting proliferation through activating cell cycle genes, and concurrently repress differentiation-promoting factors via H3K27me3. Second, callus cells exhibit a unique transcriptional profile enriched in diverse developmental regulators, thereby maintaining a primed pluripotent state that enables a rapid regenerative response. This strategy relies on a mechanism to silence the pluripotency network in response to regenerative stimuli, allowing a single developmental pathway to predominate. To test whether the Polycomb Repressive Complex 2 (PRC2), which mediates H3K27me3 silencing, is essential for maintaining callus identity and regenerative capacity, we analyzed the transcriptional state of Arabidopsis thaliana wild-type and PRC2 mutant emf2 calli. In emf2 mutants, many differentiation-associated transcription factors were up-regulated, and regenerative capacity was severely impaired. Our findings provide new insight into how pluripotency is regulated. We propose a novel model in which PRC2 governs callus identity and regenerative potential.

Abscisic acid (ABA), a phytohormone that affects key biological processes, is best known for causing stomata closure to protect plants against environmental stresses. The prevailing mechanism for ABA perception is through the PYL/PYR/RCAR family of proteins but reports of other ABA-interacting proteins such as the guard cell outward rectifying K+ channel (GORK), have encouraged the search for more ABA-sensitive proteins. Here, we identified a similar ABA-interacting site as GORK, in an Arabidopsis thaliana ANTHRANILATE SYNTHASE (ASA2). We found that asa2 mutant plants have obvious aberration in ABA-dependent stomata closing. Leaf transcriptomics revealed significantly fewer ABA-induced DEGs in asa2-1 as compared to Col-0. ABA- and other hormone-related terms were also under-represented, indicating an overall reduced genomic sensitivity to ABA. Computational analysis hinted plausible ABA interaction at the predicted site and both indirect and direct in vitro interaction studies showed that ASA2 could interact with ABA in a specific and ligand dependent manner. Importantly, single amino acid substitutions at the ABA site resulted in various degrees of reduced ABA affinities. Further examination of how ABA interaction affects the enzymatic activity of ASA2 and the flow of information in the chloroplast could reveal molecular targets for agrochemical design that will improve plant resilience.