Redesigning a S-nitrosylated pyruvate-dependent GABA transaminase 1 to generate high-malate and saline-alkali-tolerant tomato

Open stomata 1 and phosphate starvation response 1 regulate tomato root system architecture during heterogeneous phosphate availability

Plants frequently encounter uneven phosphate (Pi) distribution, yet most studies focuses on uniform low-Pi conditions. SUCROSE NONFERMENTING1-RELATED KINASE 2.6 (SnRK2.6) protein, also known as Open stomata 1 (OST1), is well-characterized in ABA signaling and stress responses. However, its role in low-Pi response is poorly understood. We investigated root system architecture (RSA) remodeling under uneven Pi distribution. Using split-root tomato plants with half roots in sufficient Pi (+Pi) and half in low Pi (-Pi), we observed low-Pi responses in both root sectors. Local low-Pi triggered the ABA accumulation in the local root regions, generating spatially distinct OST1 expression patterns. In mechanism, phosphate starvation response 1 (PHR1) directly binds to the OST1 promoter, activating its expression its expression under low-Pi conditions. This localized OST1 transcriptional regulation mediated both local and systemic RSA adaptations. Crucially, these Pi-responsive RSA remodeling were completely absent in ost1 and notabilis (not) mutants. These findings demonstrate that spatial phosphate availability shapes tomato root architecture through ABA-dependent OST1 activation and PHR1-mediated transcriptional regulation, identifying a previously unknown adaptive response to nutrient heterogeneity.

Brassinosteroid-induced S-nitrosylation of fructose-1,6-bisphosphate aldolase increased ATP synthesis under low temperatures in mini Chinese cabbage seedlings

Low temperature causes an imbalance in plant energy metabolism homeostasis. Brassinosteroids (BRs) are a class of hormones with important regulatory functions in plant responses to low temperature. S-nitrosylation of proteins is a key pathway for nitric oxide-mediated regulation of plant stress. In this study, we investigated whether S-nitrosylation proteins are involved in regulating energy metabolism in mini Chinese cabbage seedlings at low temperature. Low temperature inhibited the transcriptional accumulation of BrFBA2, BrGAPDH, BrPGK, and BrPK. However, applying exogenous BR and S-nitrosoglutathione significantly upregulated the transcription of these genes and accelerated the release of ATP. Exogenous BR significantly upregulated the S-nitrosylation level of fructose-1,6-bisphosphate aldolase 2 (FBA2) at low temperatures. FBA2 protein S-nitrosylation modification occurred in vitro at Cys-197. OE-BrFBA2 lines showed enhanced S-nitrosylation at low temperatures. Applying exogenous BR enhanced the S-nitrosylation of FBA2 and accelerated ATP release in TRV2-BrFBA2 lines. Exogenous BR treatment was conducive to maintaining the homeostasis of cell energy metabolism in mini Chinese cabbage seedlings at low temperature.

Protein post-translational modifications (PTMS) unlocking resilience to abiotic stress in horticultural crops: A review

Horticultural crops are extensively cultivated throughout the world as crucial economical crops, encompassing fruits, vegetables, ornamentals, medicinal and beverage plants, for purposes such as food supply, special nutrition provision, medical application or aesthetic enjoyment. However, abiotic stress triggered by extreme climate change, such as excessive salt and prolonged drought, directly leads to the decline of nutritional quality of horticultural crops, contributing to the shortage of high-quality fruits. Post-translational modifications of proteins, such as phosphorylation and ubiquitination, can alter protein characteristics by adding specific groups to amino acids, which in turn impacts protein stability to regulate plant growth and development as well as environmental stress. Consequently, the revelation of the molecular mechanism of horticultural crops response to abiotic stress at post-translational modification level (PTMs) has always attracted a lot of scholars, as it is crucial for the development and breeding of climate-resilient apple varieties. At PTMs level, this review focuses on summarizing research advancements in horticultural crops responses to environmental stress, including drought, salt, cold, high temperature and iron (Fe) deficiency, with emphasis on sucrose non-fermentative 1 (SNF1) associated protein kinases (SnRKs) and mitogen-activated protein kinase (MAPK) cascade mediated phosphorylation, E3 ubiquitin ligases and BTB/TAZ subfamily BT2 mediated ubiquitination, SIZ1 SUMO E3 ligase mediated sumoylation, Nitric oxide (NO) mediated S-nitrosylation, and other forms of PTMs including protein glycosylation and lysine acetylation. In conclusion, this review adopts protein modification as an entry point to illuminate the mechanism of key genes regulating abiotic stress at PTMs level, providing a foundation for the cultivation of horticultural crops with superior resistance.

Jasmonic acid and nitric oxide orchestrate a hierarchical melatonin cascade for Botrytis cinerea resistance in tomato

Tomato gray mold, caused by Botrytis cinerea (B. cinerea), poses a major challenge to tomato production. In plants, B. cinerea resistance is positively regulated by melatonin; however, the regulatory mechanism of melatonin biosynthesis during B. cinerea infection is not known. Here, we established the working model of jasmonic acid (JA) and nitric oxide (NO) on melatonin biosynthesis in the state of B. cinerea infection. NO responded to B. cinerea infection earlier than JA. In the early stage of infection, tomato caffeic acid O-methyltransferase 2 (SlCOMT2) was S-nitrosylated by NO at Cys344, enhancing the stability of SlCOMT2 and preventing its degradation via the 26S proteasome. In the late stage of infection, JA-triggered SlMYC2 bound to SlCOMT1 and SlCOMT2 promoters for their transcription. NO and JA synergistically enhanced COMT-mediated melatonin biosynthesis during B. cinerea infection via post-translational modification and transcriptional activation. The accumulation of melatonin in tomato leaves inhibited cell death by scavenging reactive oxygen species, thereby preventing B. cinerea from establishing infection sites. We propose that SlCOMT2Cys344 is a genetic manipulation site or biological breeding target that can be used to enhance melatonin synthesis and B. cinerea resistance in tomato.

Melatonin confers saline-alkali tolerance in tomato by alleviating nitrosative damage and S-nitrosylation of H+-ATPase 2

Soil salinization and alkalization disrupt redox homeostasis, impairing plant survival and crop production. Disruption of redox homeostasis can cause accumulation of reactive nitrogen species, such as nitric oxide (NO), which causes nitrosative damage in which the properties of biomacromolecules are altered. It is unclear whether melatonin regulates NO homeostasis, thereby affecting plant saline-alkali tolerance. In tomato (Solanum lycopersicum), excess NO caused by saline-alkali stress resulted in nitrosative damage, which was alleviated by S-nitrosoglutathione reductase (GSNOR). Moreover, saline-alkali stress-triggered NO stimulated caffeic acid O-methyltransferase (COMT) transcription and melatonin biosynthesis to scavenge excess NO and alleviate nitrosative damage at the proteome level. Under saline-alkali stress, plasma membrane-localized H+-ATPase 2 (HA2) was S-nitrosylated at Cys206, impairing its interaction with 14-3-3 protein 1 (TFT1). HA2 S-nitrosylation resulted in reduced HA activity, H+ efflux, and saline-alkali tolerance. Conversely, COMT-generated melatonin alleviated HA2 S-nitrosylation, recovering its function and tomato saline-alkali tolerance. Therefore, we propose that melatonin and NO are redox switches of HA2 S-nitrosylation for saline-alkali tolerance. Under natural saline-alkali conditions, tomato productivity was improved by grafting with COMT-, GSNOR-, or HA2-overexpression rootstocks, or by generating nonnitrosylated HA2C206S mutants. By establishing the melatonin-NO-HA2 module, this study illuminates a molecular function of melatonin and suggests possible genetic engineering strategies to improve agriculture.

High-nitrogen-induced γ-aminobutyric acid triggers host immunity and pathogen oxidative stress tolerance in tomato and Ralstonia solanacearum interaction

Soil nitrogen (N) significantly influences the interaction between plants and pathogens, yet its impact on host defenses and pathogen strategies via alterations in plant metabolism remains unclear. Through metabolic and genetic studies, this research demonstrates that high-N-input exacerbates tomato bacterial wilt by altering γ-aminobutyric acid (GABA) metabolism of host plants. Under high-N conditions, the nitrate sensor NIN-like protein 7 (SlNLP7) promotes the glutamate decarboxylase 2/4 (SlGAD2/4) transcription and GABA synthesis by directly binding to the promoters of SlGAD2/4. The tomato plants with enhanced GABA levels showed stronger immune responses but remained susceptible to Ralstonia solanacearum. This led to the discovery that GABA produced by the host actually heightens the pathogen's virulence. We identified the R. solanacearum LysR-type transcriptional regulator OxyR protein, which senses host-derived GABA and, upon interaction, triggers a response involving protein dimerization that enhances the pathogen's oxidative stress tolerance by activating the expression of catalase (katE/katGa). These findings reveal GABA's dual role in activating host immunity and enhancing pathogen tolerance to oxidative stress, highlighting the complex relationship between tomato plants and R. solanacearum, influenced by soil N status.

Relationship between the GABA Pathway and Signaling of Other Regulatory Molecules

GABA (gamma-aminobutyric acid) is an amino acid whose numerous regulatory functions have been identified in animal organisms. More and more research indicate that in plants, this molecule is also involved in controlling basic growth and development processes. As recent studies have shown, GABA plays an essential role in triggering plant resistance to unfavorable environmental factors, which is particularly important in the era of changing climate. The main sources of GABA in plant cells are glutamic acid, converted in the GABA shunt pathway, and polyamines subjected to oxidative degradation. The action of GABA is often related to the activity of other messengers, including phytohormones, polyamines, NO, H2O2, or melatonin. GABA can function as an upstream or downstream element in the signaling pathways of other regulators, acting synergistically or antagonistically with them to control cellular processes. Understanding the role of GABA and its interactions with other signaling molecules may be important for developing crop varieties with characteristics that enable adaptation to a changing environment.