Jiqing Wang

Key message ClTCP4 mitigates the damage of the cellular membrane and photosystem impairment from reactive oxygen species (ROS) under drought conditions by maintaining the generation of antioxidant enzymes and osmotic regulatory substances. Abstract The increasing occurrence of extreme weather events in recent years has intensified water scarcity in watermelon cultivation, significantly reducing both yield and quality. At present, the exploration of watermelon drought resistance genes is limited, which limits the use of molecular breeding for drought resistance. In current study, we identified CINCINNATA (CIN) subclass members of the TEOSINTE BRANCHED 1/CYCLOIDEA/PCF (TCP) family in watermelon through sequence alignment and homologous clustering analysis. Analysis of the gene expression characteristics showed that CIN-TCP members are induced by exogenous hormones and abiotic stresses. Specifically, the ClTCP4 is significantly induced by dehydration stress and abscisic acid (ABA). The gene-edited lines (CR lines) of ClTCP4 were constructed and were used to confirm its role in regulating the drought tolerance. Under drought stress, CR lines showed earlier leaf wilting, smaller stomatal opening, lower leaf water holding capacity and photosynthetic efficiency compared with YL plants. By combining phenotypic observation, physiologic, biochemical, and molecular experiments, our study reveals that ClTCP4 regulates the photosynthesis-related processes under drought stress through stomatal conductance pathway, mitigates the damage of the cellular membrane and possible photosystem impairment from reactive oxygen species (ROS) under drought conditions by maintaining the generation of antioxidant enzymes and osmotic regulatory substances. This study elucidates the role of ClTCP4, a member of CIN-TCP in drought stress, and could provide a theoretical foundation and gene resource for watermelon drought resistance breeding.

Key message A plant growth regulator, 5-aminolevulinic acid, enhanced the saline-alkali tolerance via photosynthetic, oxidative-reduction, and glutathione metabolism pathways in pepper seedlings. Abstract Saline-alkali stress is a prominent environmental problem, hindering growth and development of pepper. 5-Aminolevulinic acid (ALA) application effectively improves plant growth status under various abiotic stresses. Here, we evaluated morphological, physiological, and transcriptomic differences in saline-alkali-stressed pepper seedlings after ALA application to explore the impact of ALA on saline-alkali stress. The results indicated that saline-alkali stress inhibited plant growth, decreased biomass and photosynthesis, altered the osmolyte content and antioxidant system, and increased reactive oxygen species (ROS) accumulation and proline content in pepper seedlings. Conversely, the application of exogenous ALA alleviated this damage by increasing the photosynthetic rate, osmolyte content, antioxidant enzyme activity, and antioxidants, including superoxide dismutase, catalase, glutathione reductase, and glutathione peroxidase, and reducing glutathione to reduce ROS accumulation and malonaldehyde content. Moreover, the transcriptomic analysis revealed the differentially expressed genes were mainly associated with photosynthesis, oxidation–reduction process, and glutathione metabolism in saline-alkali stress + ALA treatment compared to saline-alkali treatment. Among them, the change in expression level in CaGST, CaGR, and CaGPX was close to the variation of corresponding enzyme activity. Collectively, our findings revealed the alleviating effect of ALA on saline-alkali stress in pepper seedlings, broadening the application of ALA and providing a feasible strategy for utilize saline-alkali soil.

Salt and osmotic stress seriously restrict the growth, development, and productivity of horticultural crops in the greenhouse. The papain-like cysteine proteases (PLCPs) participate in multi-stress responses in plants. We previously demonstrated that salt and osmotic stress affect cysteine protease 15 of pepper (Capsicum annuum L.) (CaCP15); however, the role of CaCP15 in salt and osmotic stress responses is unknown. Here, the function of CaCP15 in regulating pepper salt and osmotic stress resistance was explored. Pepper plants were subjected to abiotic (sodium chloride, mannitol, salicylic acid, ethrel, methyl jasmonate, etc.) and biotic stress (Phytophthora capsici inoculation). The CaCP15 was silenced through the virus-induced gene silencing (VIGS) and transiently overexpressed in pepper plants. The full-length CaCP15 fragment is 1568 bp, with an open reading frame of 1032 bp, encoding a 343 amino acid protein. CaCP15 is a senescence-associated gene 12 (SAG12) subfamily member containing two highly conserved domains, Inhibitor 129 and Peptidase_C1. CaCP15 expression was the highest in the stems of pepper plants. The expression was induced by salicylic acid, ethrel, methyl jasmonate, and was infected by Phytophthora capsici inoculation. Furthermore, CaCP15 was upregulated under salt and osmotic stress, and CaCP15 silencing in pepper enhanced salt and mannitol stress resistance. Conversely, transient overexpression of CaCP15 increased the sensitivity to salt and osmotic stress by reducing the antioxidant enzyme activities and negatively regulating the stress-related genes. This study indicates that CaCP15 negatively regulates salt and osmotic stress resistance in pepper via the ROS-scavenging.

To select the optimum fertilizer application under specific irrigation levels and to provide a reliable fertigation system for tomato plants, an experiment was conducted by using a microporous membrane for water-fertilizer integration under non-pressure gravity. A compound fertilizer (N:P₂O₅:K₂O, 18:7:20) was adopted for topdressing at four levels, 1290 kg/ha, 1140 kg/ha, 990 kg/ha, and 840 kg/ha, and the locally recommended level of 1875 kg/ha was used as the control to explore the effects of different fertilizer application rates on growth, nutrient distribution, quality, yield, and partial factor of productivity (PFP) in tomato. The new regime of microporous membrane water-fertilizer integration under non-pressure gravity irrigation reduced the fertilizer application rate while promoting plant growth in the early and intermediate stages. Except for the 990 kg/ha fertilizer treatment, yields per plant and per plot for each fertilizer application rate were higher than or equal to those of the control. The new regime could effectively improve PFP and reduce soil nutrient enrichment. Fertilizer at 840 kg/ha showed the optimum results by increasing PFP by 75.72% as compared to control. In conclusion, the fertilizer rate at 840 kg/ha has not only maintained the productivity of soil but also tomato growth and quality of fruit which makes the non-pressure gravity irrigation a potential and cost-effective way for fertilizer application.

Potassium fulvic acid and diethyl aminoethyl hexanoate (DA-6) are two kinds of growth regulators with yield increasing and quality improving. There are few reports on the effects of adding potassium fulvic acid and DA-6 in nutrient solution on the growth of soilless culture of vegetables. In this study, tomato was used as the test material to add different concentrations of potassium fulvic acid (0, 15, 30 mg•L-1) and DA-6 (0, 2.5, 5 mg•L-1) into nutrient solution of total nutrient minerals, so as to study the effects of adding two growth-regulating substances to nutrient solution of total nutrient mineral on the growth, yield and quality of tomato in soilless cultivation with rock wool in solar greenhouse. The results showed that: With no addition of potassium fulvic acid and DA-6 as the control, in the early stage of bearing fruit, the potassium fulvic acid added with 30 mg•L-1 nutrient solution alone had an inhibitory effect on tomato plant height and the inhibition could be alleviated by adding DA-6. When 30 mg•L-1 potassium fulvic acid and DA-6 were added together, the fresh quality of single stem and dry quality of single leaf in the early and middle stage of tomato bearing fruit were significantly improved. 15 mg•L-1 potassium fulvic acid and 2.5 mg•L-1 DA-6 had the best effect on the total yield of a single plant, which was 21.77% higher than that of the control. 15 mg•L-1 potassium fulvic acid and DA-6 could significantly increase the C content and sugar acid ratio of tomato fruit. To summarize, 15 mg•L-1 potassium fulvic acid and 2.5 mg•L-1 DA-6 showed synergistic effect, which has the best improvement effect on the growth, yield and quality of best.