Melatonin mediates elevated carbon dioxide-induced photosynthesis and thermotolerance in tomato.

Increasing carbon dioxide (CO2 ) promotes photosynthesis and mitigates heat stress-induced deleterious effects on plants, but the regulatory mechanisms remain largely unknown. Here, we found that tomato (Solanum lycopersicum L.) plants treated with high atmospheric CO2 concentrations (600, 800, and 1000 µmol mol-1 ) accumulated increased levels of melatonin (N-acetyl-5-methoxy tryptamine) in their leaves and this response is conserved across many plant species, including Arabidopsis, rice, wheat, mustard, cucumber, watermelon, melon, and hot pepper. Elevated CO2 (eCO2 ; 800 µmol mol-1 ) caused a 6.8-fold increase in leaf melatonin content, and eCO2 -induced melatonin biosynthesis preferentially occurred through chloroplast biosynthetic pathways in tomato plants. Crucially, manipulation of endogenous melatonin levels by genetic means affected the eCO2 -induced accumulation of sugar and starch in tomato leaves. Furthermore, net photosynthetic rate, maximum photochemical efficiency of photosystem II, and transcript levels of chloroplast- and nuclear-encoded photosynthetic genes, such as rbcL, rbcS, rbcA, psaD, petB, and atpA, significantly increased in COMT1 overexpressing (COMT1-OE) tomato plants, but not in melatonin-deficient comt1 mutants at eCO2 conditions. While eCO2 enhanced plant tolerance to heat stress (42°C) in wild-type and COMT1-OE, melatonin deficiency compromised eCO2 -induced thermotolerance in comt1 plants. The expression of heat shock proteins genes increased in COMT1-OE but not in comt1 plants in response to eCO2 under heat stress. Further analysis revealed that eCO2 -induced thermotolerance was closely linked to the melatonin-dependent regulation of reactive oxygen species, redox homeostasis, cellular protein protection, and phytohormone metabolism. This study unveiled a crucial mechanism of elevated CO2 -induced thermotolerance in which melatonin acts as an essential endogenous signaling molecule in tomato plants.

Molecular Mechanisms of Autophagy Regulation in Plants and Their Applications in Agriculture.

Autophagy is a highly conserved cellular process for the degradation and recycling of unnecessary cytoplasmic components in eukaryotes. Various studies have shown that autophagy plays a crucial role in plant growth, productivity, and survival. The extensive functions of plant autophagy have been revealed in numerous frontier studies, particularly those regarding growth adjustment, stress tolerance, the identification of related genes, and the involvement of metabolic pathways. However, elucidation of the molecular regulation of plant autophagy, particularly the upstream signaling elements, is still lagging. In this review, we summarize recent progress in research on the molecular mechanisms of autophagy regulation, including the roles of protein kinases, phytohormones, second messengers, and transcriptional and epigenetic control, as well as the relationship between autophagy and the 26S proteasome in model plants and crop species. We also discuss future research directions for the potential application of autophagy in agriculture.

[Effects of electroacupuncture at "Baihui" and "Yongquan" on the levels of synaptic plasticity related proteins postsynaptic density-95 and synaptophysin in hippocampus of APP/PS1 mice].

OBJECTIVE: From the perspective of ß-amyloid (Aß) toxicity and synaptic plasticity, the mechanism of electroacupuncture to improve learning and memory ability in the early pathological stages of Alzheimer's disease was explored. METHODS: Twelve male amyloid-protein precursor (APP)/γ-secretase (PS1) double transgenic AD mice were randomly and equally divided into electroacupuncture (EA) group and model group, and other 6 male C57BL/6 mice were used as the normal group. EA (1 Hz/50 Hz, 0.5 mA) was applied to "Baihui" (GV20) and bilateral "Yongquan"(KI1) for 15 min, once every other day for 6 weeks. Immunofluorescence was used to observe the positive expression of Aß in the left hippocampus. Immunohistochemistry was used to observe the positive expression of postsynaptic density-95 (PSD-95) in the left hippocampus. Western blot was used to detect the expression of PSD-95 and synaptophysin (SYN)in the right hippocampus. RESULTS: Immunofluorescence results showed that extracellular Aß was seen in the model group and electroacupuncture group, but no senile plaques were seen. Compared with the normal group, the expression level of Aß in the hippocampus of the model group increased significantly (P<0.01). Compared with the model group, the expression of Aß in the hippocampus of the EA group decreased (P<0.05). Immunohistochemical results showed that compared with the normal group, the PSD-95 positive expression in the model group was decreased(P<0.05). Compared with the model group, the expression of PSD-95 in the EA group was increased (P<0.05). Western blot results showed that compared with the normal group, the expression levels of PSD-95 and SYN in the hippocampus of the model group were decreased (P<0.05, P<0.01). Compared with the model group, the expression levels of PSD-95 and SYN in the EA group were increased (P<0.05，P <0.01). CONCLUSION: EA can reduce the expression of Aß in the hippocampus of APP/PS1 mice and increase the expression of PSD-95 and SYN, which may contribute to its effect in improving the synaptic plasticity.