Journal of Experimental Botany最新文献

The small chloroplastic protein CP12 has multiple functions, including the regulation of enzymes in the Calvin-Benson-Bassham cycle. Here, we investigated its role in the acclimation of Chlamydomonas reinhardtii to varying CO2 availability. We showed that phosphoribulokinase can interact with CP12 in conditions where the Calvin-Benson-Bassham cycle is active. Compared to the wild type, at high CO2, C. reinhardtii CP12 deletion mutants, or partially complemented mutants, have less phosphoribulokinase and ribulose-1,5-bisphosphate (RuBP), indicating that the regeneration of RuBP is regulated, in part, by CP12. C. reinhardtii has a CO2 concentrating mechanism that increases the supply of CO2 to ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and involves, among other features, the condensation of Rubisco within the pyrenoid via its interaction with a scaffold protein named Essential Pyrenoid Component 1 (EPYC1). In CP12 deletion mutants, the expected relocation of Rubisco towards the pyrenoid was not observed upon transition from high to very low CO2, contrary to WT cells. The CP12 deletion mutants are a unique example where the induction of CO2 concentrating mechanism at very low CO2 was not accompanied by Rubisco relocation. Altogether, these results suggest that CP12 contributes to the coordination between RuBP regeneration, Rubisco location, and CO2 acquisition.

The seedling stage is critical for tree recruitment and forest regeneration, but faces high mortality rates, with drought being a major cause. However, knowledge of the hydraulic vulnerability of tree seedlings is scarce due to methodological difficulties related to their small size. We quantified the xylem vulnerability of the hypocotyl to drought-induced embolism using the ultrasonic acoustic emission (AE) and optical visualization (OV) techniques by performing simultaneous measurements on dehydrating 5-8-week-old seedlings of Acer pseudoplatanus, Sorbus aucuparia, Larix decidua and Pinus cembra. OV was also used on the angiosperm leaves. Species-specific differences in hypocotyl and leaf vulnerability were observed. AE data showed that the hypocotyl vulnerability of S. aucuparia, L. decidua and P. cembra was similar to that reported for mature tree branches. OV was similar to AE vulnerability in A. pseudoplatanus and P. cembra, but higher in L. decidua and S. aucuparia (with differences of 0.83 and 2.50 MPa, respectively). The latter showed exceptional higher frequencies in small conduits, which may be difficult to observe with OV. Both techniques can be used to provide new insights into tree seedling hydraulics, which will be crucial for better predicting forest regeneration in the face of climate change.

Understanding the dynamics of pollen release is critical for studying plant reproductive strategies, particularly in systems where pollen is aerosolized, such as wind- and buzz-pollinated flowers. However, quantifying airborne pollen remains labor-intensive and reliant on laboratory-based techniques, limiting the scope of experimental and field-based research. Here, we demonstrate the use of a handheld air particle counter as a rapid, portable, and precise method for quantifying pollen release in real time across diverse pollination systems. Using controlled vibration experiments on buzz-pollinated Melastomataceae flowers we compare pollen counts from the air particle counter to those obtained from conventional liquid particle counters. The handheld counter consistently reported more reasonable and more consistent pollen counts across species, likely due to its ability to capture dispersed pollen clouds regardless of release direction. High-speed video footage confirmed that traditional methods can miss significant portions of pollen due to directional variability from stamens with complex morphologies. We further show that the handheld particle counter is applicable beyond buzz-pollination by using it to quantify pollen release in artificial wind-pollination experiments with Betula sp. Additionally, the device allows for fine-scale measurements of pollen size distributions and real-time pollen release rates. We further show that this method is robust to variations in pollen concentration and particle speed, and that it can detect exponential decrease in concentration of wind-dispersed pollen with distance. Beyond pollen, we discuss potential applications of this technique in quantifying airborne spores, seeds, and pathogens. Our results highlight the utility of handheld particle counters for experimental fieldwork and open new avenues for studying airborne particle dispersal and reproductive trait evolution in plants.

Increasing nitrogen (N) deposition tends to aggravate phosphorus (P) limitation in subtropical forest ecosystems. Arbuscular mycorrhizal (AM) fungi are believed to improve the plant P supply under P-depleted soil conditions. However, how the AM fungi and their extraradical mycelia impact soil P transformation and subsequent P availability under N-induced P limitation is not fully understood. Using an ingrowth-core design, we quantified the effects of AM mycelia on different soil P pools and potential drivers controlling the transformation and availability of soil P in a subtropical forest receiving N fertilization. Nitrogen addition had greater positive and negative mycelial effects on the soil labile P pools and moderately labile P pools, respectively. This finding indicated that AM mycelia increased the availability of soil P under N deposition by promoting transformation from moderately labile P to labile P. Additionally, we observed diverse mycelial effects under N addition on multiple microbial (P-transformation genes and phosphatase activities) and physiochemical drivers (Al/Fe oxyhydroxides and soil pH) involved in driving soil P transformation. These results suggest that AM mycelia can improve soil P availability to counteract increased P limitation due to N deposition by controlling microbial and physiochemical processes that coregulate soil P transformation. The positive feedback effects of mycorrhizal fungi on soil P transformation and availability as well as the drivers controlling these effects should be incorporated into ecosystem biogeochemical models. This is crucial for accurately predicting forest productivity and function under future N deposition scenarios.

Tropical tree species vary in photosynthetic temperature sensitivity, with species from warmer habitats or those acclimated to higher temperatures typically displaying higher thermal optima for net CO2 assimilation (Topt, Anet). Sustaining photosynthesis at elevated temperatures likely requires increased allocation of resources (ATP, NADPH, nitrogen, carbon) toward heat stress management, particularly PSII repair. However, under extreme heat, repair demands may exceed available resources, potentially limiting acclimation. It is unclear whether higher Topt, Anet reflects inherently greater PSII heat stability. We studied 11 tropical tree species across a topographic (hilltop, slope, valley) and thermal gradient (summer peaks: 46.1, 40.1, 31.8 °C, respectively) in India's Central Western Ghats forest, measuring photosynthetic temperature responses and PSII thermal tolerance (T5, the temperature causing 5% PSII efficiency decline) at peak summer. We found an inverse correlation between T5 and Topt, Anet (p = 0.005): lower Topt, Anet was associated with higher PSII heat stability (higher T5), and vice versa. This could suggest a trade-off between investing resources to achieve higher Topt, Anet and maintaining PSII heat stability. Species may struggle to simultaneously acclimate to elevated temperatures and remain resilient to extreme heat events. These findings have implications for understanding tropical forest tree responses to climate warming.

The role of auxin in leaf vein patterning, as expressed through auxin signaling and polar transport, is well established and supported by both experimental and computational data. In contrast, the involvement of plasmodesmata (PDs) in the auxin-driven vein patterning process has only been considered in computational models. Recent experimental data have provided support for the involvement of PDs, specifically their facilitation of auxin movement, in the patterned vein formation process. This review highlights the current model for patterned vein formation in Arabidopsis, examines the various pathways by which PDs enable auxin signal movement, discusses unresolved questions arising from findings on plasmodesmata-enabled auxin signal movement (PEASM), and proposes new research questions that may provide potential mechanistic insights into leaf vein patterning mechanisms.

Plants rely on symplasmic networks of cell-to-cell communication through plasmodesmata and long-distance communication through phloem to regulate plant development and adaptations to environmental changes. Plasmodesmata facilitate the intercellular transport of metabolites, phytohormones, proteins and RNA molecules, many of which act as signaling molecules. Among these, non-cell-autonomous RNA molecules play a crucial role in coordinating plant development, gene silencing, stress responses, and nutrient allocation, as well as in antiviral defense and host-parasite interactions. This review explores the mechanisms of cell-to-cell and systemic mobility of small RNAs, with a particular emphasis on the role of virus- and host-derived small RNAs in regulating the outcome of viral infection in terms of disease, resistance and tolerance.

Plant viruses have evolved diverse strategies for cell-to-cell and systemic movement, utilizing various viral proteins and cellular components and pathways. They typically encode one or a small group of proteins called movement proteins that mediate their local cell-to-cell movement via plasmodesmata (PD). Other virus-encoded proteins also make important contributions to viral transit through PD. Movement and other viral proteins use various cellular pathways to mediate their localization to and transit through PD. This review summarizes current understanding of these pathways and mechanisms, with a focus on movement proteins and their interactions with host factors.

The tomato brown rugose fruit virus (ToBRFV) is an increasingly prevalent pathogen that poses a threat to the global tomato industry. Topical application of dsRNA has shown promise as an effective tool to control many pathogens, including viruses; however, it this has not yet been demonstrated for ToBRFV. In this study, ToBRFV-specific long dsRNA molecules were synthesized in vivo by incorporating parts of its genome into that of bacteriophage phi6, thereby enabling the amplification of the chimeric dsRNA in Pseudomonas syringae. Co-inoculation of ToBRFV and purified, high-quality (hq)-dsRNA onto tomato (Solanum lycopersicum) plants resulted in reduction of both viral RNA levels and disease symptoms. Functional analysis of the hq-dsRNA response against the virus revealed its independence of RNA-DEPENDENT RNA POLYMERASE 6 (RDR6) and SUPPRESSOR OF GENE SILENCING 3 (SGS3). In addition, non-infected plants showed a mild activation of innate immune responses upon hq-dsRNA treatment, including accumulation of callose at plasmodesmata. Overall, our results provide evidence for hq-dsRNA as a tool for controlling ToBRFV in tomato plants, and demonstrate the potential of in vivo produced dsRNA in the battle against crop pathogens.

Boosting crop productivity while enhancing resilience to climate change and disease remains a major challenge. Plasmodesmata (PD), which mediate cell-to-cell connectivity, are crucial for plant growth but remain underutilized as targets for crop improvement. This review focuses on C4 photosynthesis to demonstrate the importance of enhanced cell-to-cell connectivity to improve productivity. In C4 plants, connectivity between mesophyll (M) and bundle sheath (BS) cells is essential for building an efficient CO2-concentrating mechanism. Enhanced PD frequency at the M-BS interface is a key feature of C4 Kranz leaf anatomy, and thus an important trait to introduce in engineering C4 photosynthesis into C3 crops. We propose potential gene targets to engineer PD connectivity, while emphasizing the need for further research to discover new targets that affect PD formation and regulation. We also discuss advances in biotechnological tools that are important for both molecular studies and deploying strategies to manipulate PD in crops. These target genes and tools may ultimately unlock new capabilities to improve crop productivity and resilience by engineering cell-to-cell connectivity within various tissues.