Journal of Experimental Botany最新文献

Increases in global temperature and drought are negatively impacting the yields of major crops. Therefore, targeted improvements to intrinsic water use efficiency (WUEi) are needed to reduce the water required for agricultural production. While it is very time-consuming to directly measure WUEi, stable carbon isotope ratios (δ13C) are a reliable high throughput proxy trait for quantifying WUEi in C3 species. While genetic studies have improved our understanding of the relationship between WUEi and δ13C in C4 species, the knowledge needed to implement δ13C in breeding schemes is incomplete. Using a maize line with an extremely negative δ13C value, a quantitative genetics approach was used to identify a large deletion in carbonic anhydrase1 (cah1). Carbonic anhydrase is the first enzymatic step of the C4 photosynthetic pathway and is known to affect δ13C. Surprisingly, the line with the mutant allele had significantly higher carbonic anhydrase activity with a concurrent reduction in δ13C, the opposite of what would be expected based on C4 carbon isotope fractionation theory. These observations decouple δ13C and WUEi, which calls for further investigation into carbon isotope discrimination in C4 species.

Necrotrophic Alternaria alternata induces EXECUTER 1(EX1)/2-dependent singlet oxygen (1O2) bursts, leading to plant cell death, with jasmonic acid (JA) acting as a key signal transducer downstream of EX1/2-mediated signaling. Salicylic acid (SA), a crucial defense hormone, is known to respond to pathogen invasion and activate defense gene expression. Previous studies emphasized the importance of SA in A. alternata-induced necrosis in the light of the increased susceptibility of SA-deficient transgenic Arabidopsis NahG to A. alternata. In this study, we investigated the role of SA in A. alternata-triggered 1O2 signaling in Arabidopsis. We found that EX1/2 deficiency did not alter SA levels in Arabidopsis infected with A. alternata, indicating that SA signaling regulates A. alternata-induced pathogenesis through an EX1/2-independent pathway. Exogenous SA application and increased endogenous SA in the ssi2-2 mutant enhanced resistance but inhibited JA production. Conversely, SA signaling deficiency in the eds1 and pad4 mutants increased susceptibility and elevated JA levels. In conclusion, SA enhances Arabidopsis defense against A. alternata via an EX1/2-independent 1O2 signal pathway and antagonizes JA biosynthesis.

There has been groundbreaking progress in identifying unique functions of the plant heat shock protein Hsp90 in stress responses in recent years. However, there is an absence of systematic integration of these new mechanisms in protein quality control, hormone network regulation, chloroplast protection, and immune defense in existing reviews; this article aims to fill this gap. Recent studies have revealed four key mechanisms: (i) Hsp90 forms complexes with E3 ligases to promote polyubiquitination of heat-induced protein aggregates, cooperating with the 26S proteasome for clearance, a pathway hijacked by viruses; (ii) Hsp90 stabilizes the auxin receptor Transport inhibitor response 1 (TIR1), reconstructs root auxin gradients via polarized PIN-FORMED 1 (PIN1), activates abscisic acid (ABA) biosynthesis, and enhances insect resistance through JA signaling; (iii) Hsp90C maintains photosystem renewal, protects chloroplast DNA via CHLOROPLAST-AND-NUCLEUS DUAL-LOCALIZED PROTEIN 1 (CND1) translocation, and stabilizes thylakoid proteins via its CTE domain; and (iv) Hsp90 escorts Chitin Elicitor Receptor Kinase 1 (CERK1) to initiate pattern-triggered immunity (PTI), activates nucleotide binding leucine-rich repeat (NLR) for effector-triggered immunity (ETI), and interacts with Autophagy-related protein 8 (ATG8) to enhance autophagic pathogen clearance. This review integrates key new discoveries since 2012 and identifies core research gaps to address: regulation of optimal threshold of Hsp90 abundance, its combined stress response mechanism, transformation of knowledge from model plants to major food crops. The article provides a clear direction framework for subsequent research.

The effects of ongoing anthropogenic climate change are not well known in marine diatoms, a key group of primary producers. Specifically, detailed characterizations of their carbon-concentrating mechanisms (CCMs) are lacking, which limits the understanding of how changing ocean carbonate chemistry will impact global primary production. While the model diatom Thalassiosira pseudonana has been widely studied, contrasting results have prevented the clear elucidation of its CCM. A quantitative proteomic analysis was therefore performed across three experimental treatments (low pCO2/high pH, high pCO2/low pH, low pCO2/low pH) to discern the specific roles of proteins that can be involved in both CCMs and other cellular processes (e.g. pH regulation). The results suggest a hybrid CCM consisting of both biophysical and biochemical steps that facilitate increased CO2 diffusion into the cell, the formation and transport of an organic carbon intermediate into the chloroplast, the subsequent decarboxylation of this intermediate, and the facilitated diffusion of inorganic carbon into the pyrenoid-penetrating thylakoid. No evidence supporting roles for candidate CCM proteins in pH regulation, cyclic electron transport, or excess energy dissipation was found. As each CCM step still requires functional validation, common challenges inherent to CCM research are discussed and strategies to overcome them are suggested.

Stems play diverse roles across different plant species and developmental stages. In cauliflower, both stem growth and resource allocation to the curd remain under-investigated, so in this study we examined stem and curd growth dynamics to identify potential connections between these processes. We found that the stem dry weight and length increased from budding to the stage of commercial maturity, whilst stem dry matter accumulation during this period was negatively correlated with stem length at budding and also with curd yield, implying that the stem acts as a sink organ and potentially competes with the curd. Module trait analysis of transcriptomic data revealed a strong correlation between brassinosteroid (BR)-related pathways and stem length and sink capacity. Treatment of seedlings and plants at the rapid elongation stage with the BR biosynthesis inhibitor propiconazole (PCZ) reduced stem dry matter accumulation and length, confirming that BR positively regulates these traits. Notably, treatment with 1000 μM PCZ increased curd yields in field-grown cauliflower and broccoli, and was associated with higher sucrose, cellulose, and dry matter accumulation in the curds, and enhanced the harvest index. Thus, our study shows that cauliflower yield can be increased by optimizing resource distribution between the stem and curd.

Plant pathogens rely on host-derived nutrients for proliferation, yet the mechanisms by which hosts supply these nutrients remain incompletely understood. Here, we show that infection of Arabidopsis thaliana by the necrotrophic fungus Botrytis cinerea leads to increased accumulation of the amino acid transporter UmamiT20 in leaf veins surrounding the lesions. Functional assays demonstrate that UmamiT20 mediates amino acid transport of a wide range of neutral amino acids. Consistent with a role during infection, umamiT20 knockout mutants displayed significantly reduced susceptibility to B. cinerea. Our findings extend the concept of transporter-mediated susceptibility beyond the SWEET sugar transporters in bacterial blight of rice, cassava, and cotton, to a necrotrophic fungus and implicate nutrients other than sucrose, namely amino acids, in nutrition or nutrient signaling related to immunity. We hypothesize that stacking of mutations in different types of susceptibility-related nutrient carriers to interfere with access to several nutrients may enable engineering of robust pathogen resistance in a wide range of plant-pathogen systems.

The mechanistic aspects of resource availability on carbon allocation to growth or defense of plants has been widely discussed. This study tests the growth-defense trade-off framework by comparing rates of carbon assimilation and secondary metabolite production in novel time scales in N-limited sunflower. Upon exposure to N deficiency, increased accumulation of caffeoylquinic acid derivatives in leaf and root tissue was detected, which, however, represented only a small fraction of the assimilated carbon. Furthermore, there was no increased production of lignin under N limitation. Instead, the 'excess' of assimilated carbon not used for leaf expansion was largely allocated to the roots for vegetative processes. Lastly, an active steering of caffeoylquinic acid biosynthesis was indicated by increased expression of hydroxycinnamoyl CoA:quinate hydroxycinnamoyl transferase 3. Despite a relatively late reduction of the N concentration in the plants, it could not be definitively resolved to what extent changes in the physiological C/N balance may have influenced caffeoylquinic acid formation. Nevertheless, there is no definitive support for the mass-action-based accumulation of secondary metabolites suggested by a traditional view of the growth-defense trade-off framework. One may assume that the correlation of resource availability and defense investment has been shaped by complex evolutionary processes and is coordinated by tightly regulated biochemical networks, although it may be triggered by carbon/nutrient imbalance at the cellular scale.

The cell wall plays a key role in determining mesophyll conductance (gm) and photosynthetic capacity. While the impact of wall thickness (Tcw) on gm is well understood, the influence of wall composition and structural interactions on Tcw and gm remains unclear, and it is unknown whether these factors have been affected during crop domestication. In this study, we examined 25 wild and 13 domesticated Gossypium genotypes to investigate whether variations in Tcw, composition, and structure affected gm and photosynthesis. X-ray diffraction was used to analyze internal cell wall structure. Cotton domestication reduced Tcw by modifying the pectin-to-(cellulose+hemicellulose) ratio and increasing cellulose crystallinity. However, cell wall composition and structure regulate gm differently in wild and domesticated genotypes. In wild genotypes, the pectin-to-(cellulose+hemicellulose) ratio influences CO2 diffusion, while in domesticated genotypes, the pectin matrix may be more compact, making 1/(pectin+cellulose+hemicellulose) a better predictor, reflecting the internal property differences of the cell wall. We suggest that the exceptionally low Tcw values reported in cotton domesticated genotypes indicate that they have reached the lower limit, which may impose physical constraints on component proportions and conformation.

Soil salinity is a major threat to sustainability and profitability of agricultural production systems and food security of future generations. Plants respond to salinity-induced constraints by activating numerous adaptive responses that operate in a strict tissue- and cell-specific manner and require coordination at the whole-plant level. Central to this process is the root-to-shoot signaling. Being the first organ to sense saline conditions in the rhizosphere, roots produce various signals that are then propagated through the plant, enabling the coordination and integration of physiological processes across different organs and tissues. These signals can be of different nature and include physical (electric and hydraulic signals; propagating reactive oxygen species and Ca2+ waves), chemical (hormones, photoassimilates, and nutrients), and molecular (peptides, proteins, and miRNAs) signals. Each category of long-distance signals has its own origin, transport mechanism, target tissue(s), function, and interaction with other signals. In this work, we summarize the current knowledge of such long-distance signaling in plants grown under saline conditions, with a specific focus on halophytes-naturally 'salt-loving' plants. Our aim is to reveal specific signaling traits that confer salinity stress tolerance that can then be used as new targets in breeding programs aimed to improve salinity stress tolerance in crops.