Jasmonate Positively Regulates Cold Tolerance by Promoting ABA Biosynthesis in Tomato

Comparative physiology and transcriptome response patterns in cold-tolerant and cold-sensitive varieties of Solanum melongena

BACKGROUND

Climate change has led to severe cold events, adversely impacting global crop production. Eggplant (Solanum melongena L.), a significant economic crop, is highly susceptible to cold damage, affecting both yield and quality. Unraveling the molecular mechanisms governing cold resistance, including the identification of key genes and comprehensive transcriptional regulatory pathways, is crucial for developing new varieties with enhanced tolerance.

RESULTS

In this study, we conducted a comparative analysis of leaf physiological indices and transcriptome sequencing results. The orthogonal partial least squares discriminant analysis (OPLS-DA) highlighted peroxidase (POD) activity and soluble protein as crucial physiological indicators for both varieties. RNA-seq data analysis revealed that a total of 7024 and 6209 differentially expressed genes (DEGs) were identified from variety "A" and variety "B", respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment of DEGs demonstrated that the significant roles of starch and sucrose metabolism, glutathione metabolism, terpenoid synthesis, and energy metabolism (sucrose and starch metabolism) were the key pathways in eggplant. Weighted gene co-expression network analysis (WGCNA) shown that the enrichment of numerous cold-responsive genes, pathways, and soluble proteins in the MEgrep60 modules. Core hub genes identified in the co-expression network included POD, membrane transporter-related gene MDR1, abscisic acid-related genes, growth factor enrichment gene DELLA, core components of the biological clock PRR7, and five transcription factors. Among these, the core transcription factor MYB demonstrated co-expression with signal transduction, plant hormone, biosynthesis, and metabolism-related genes, suggesting a pivotal role in the cold response network.

CONCLUSION

This study integrates physiological indicators and transcriptomics to unveil the molecular mechanisms responsible for the differences in cold tolerance between the eggplant cold-tolerant variety "A" and the cold-sensitive variety "B". These mechanisms include modulation of reactive oxygen species (ROS), elevation in osmotic carbohydrate and free proline content, and the expression of terpenoid synthesis genes. This comprehensive understanding contributes valuable insights into the molecular underpinnings of cold stress tolerance, ultimately aiding in the improvement of crop cold tolerance.

Jasmonates Promote β-Amylase-Mediated Starch Degradation to Confer Cold Tolerance in Tomato Plants

Cold stress severely restricts growth and development, reduces yields, and impairs quality in tomatoes (Solanum lycopersicum). Amylase-associated starch degradation and soluble sugar accumulation have been implicated in adaptation and resistance to abiotic stress. Here, we report a β-amylase (BAM) gene, SlBAM3, which plays a central role in tomato cold tolerance. The expression of SlBAM3 was triggered by cold stress. SlBAM3 knockout using the CRISPR/Cas9 system retarded starch degradation and reduced soluble sugar accumulation in tomato plants, eventually attenuating cold tolerance. Expression analysis revealed that the SlBAM3 transcript level was boosted by MeJA. Furthermore, MYC2, an essential component of the JA signaling pathway, could bind to the SlBAM3 promoter and directly activate SlBAM3 transcription, as revealed by yeast one-hybrid and dual LUC assays. In addition, the suppression of MYC2 resulted in increased starch accumulation, decreased soluble sugar content, and reduced tolerance to cold stress in tomato plants. Taken together, these findings demonstrate that JA positively regulates β-amylase-associated starch degradation through the MYC2-SlBAM3 module in tomato during cold stress. The results of the present work expand our understanding of the mechanisms underlying BAM gene activation and starch catabolism under cold stress. The regulatory module of SlBAM3 can be further utilized to breed tomato cultivars with enhanced cold tolerance.

A novel miR160a-GmARF16-GmMYC2 module determines soybean salt tolerance and adaptation

Salt stress is a major challenge that has a negative impact on soybean growth and productivity. Therefore, it is important to understand the regulatory mechanism of salt response to ensure soybean yield under such conditions. In this study, we identified and characterized a miR160a-GmARF16-GmMYC2 module and its regulation during the salt-stress response in soybean. miR160a promotes salt tolerance by cleaving GmARF16 transcripts, members of the Auxin Response Factor (ARF) family, which negatively regulates salt tolerance. In turn, GmARF16 activates GmMYC2, encoding a bHLH transcription factor that reduces salinity tolerance by down-regulating proline biosynthesis. Genomic analysis among wild and cultivated soybean accessions identified four distinct GmARF16 haplotypes. Among them, the GmARF16H3 haplotype is preferentially enriched in localities with relatively saline soils, suggesting GmARF16H3 was artificially selected to improve salt tolerance. Our findings therefore provide insights into the molecular mechanisms underlying salt response in soybean and provide valuable genetic targets for the molecular breeding of salt tolerance.

Extracellular Self- and Non-Self DNA Involved in Damage Recognition in the Mistletoe Parasitism of Mesquite Trees

Psittacanthus calyculatus parasitizes mesquite trees through a specialized structure called a haustorium, which, in the intrusive process, can cause cellular damage in the host tree and release DAMPs, such as ATP, sugars, RNA, and DNA. These are highly conserved molecules that primarily function as signals that trigger and activate the defense responses. In the present study, we generate extracellular DNA (exDNA) from mesquite (P. laevigata) tree leaves (self-exDNA) and P. calyculatus (non-self exDNA) mistletoe as DAMP sources to examine mesquite trees' capacity to identify specific self or non-self exDNA. We determined that mesquite trees perceive self- and non-self exDNA with the synthesis of O2•-, H2O2, flavonoids, ROS-enzymes system, MAPKs activation, spatial concentrations of JA, SA, ABA, and CKs, and auxins. Our data indicate that self and non-self exDNA application differs in oxidative burst, JA signaling, MAPK gene expression, and scavenger systems. This is the first study to examine the molecular biochemistry effects in a host tree using exDNA sources derived from a mistletoe.

Jasmonate: A Hormone of Primary Importance for Temperature Stress Response in Plants

Temperature is a critical environmental factor that plays a vital role in plant growth and development. Temperatures below or above the optimum ranges lead to cold or heat stress, respectively. Temperature stress retards plant growth and development, and it reduces crop yields. Jasmonates (JAs) are a class of oxylipin phytohormones that play various roles in growth, development, and stress response. In recent years, studies have demonstrated that cold and heat stress affect JA biosynthesis and signaling, and JA plays an important role in the response to temperature stress. Recent studies have provided a large body of information elucidating the mechanisms underlying JA-mediated temperature stress response. In the present review, we present recent advances in understanding the role of JA in the response to cold and heat stress, and how JA interacts with other phytohormones during this process.

Genome-Wide Identification and Expression Analysis of AS2 Genes in Brassica rapa Reveal Their Potential Roles in Abiotic Stress

The ASYMMETRIC LEAVES2/LATERAL ORGAN BOUNDARIES (AS2/LOB) gene family plays a pivotal role in plant growth, induction of phytohormones, and the abiotic stress response. However, the AS2 gene family in Brassica rapa has yet to be investigated. In this study, we identified 62 AS2 genes in the B. rapa genome, which were classified into six subfamilies and distributed across 10 chromosomes. Sequence analysis of BrAS2 promotors showed that there are several typical cis-elements involved in abiotic stress tolerance and stress-related hormone response. Tissue-specific expression analysis showed that BrAS2-47 exhibited ubiquitous expression in all tissues, indicating it may be involved in many biological processes. Gene expression analysis showed that the expressions of BrAS2-47 and BrAS2-10 were significantly downregulated under cold stress, heat stress, drought stress, and salt stress, while BrAS2-58 expression was significantly upregulated under heat stress. RT-qPCR also confirmed that the expression of BrAS2-47 and BrAS2-10 was significantly downregulated under cold stress, drought stress, and salt stress, and in addition BrAS2-56 and BrAS2-4 also changed significantly under the three stresses. In addition, protein-protein interaction (PPI) network analysis revealed that the Arabidopsis thaliana genes AT5G67420 (homologous gene of BrAS2-47 and BrAS2-10) and AT3G49940 (homologous gene of BrAS2-58) can interact with NIN-like protein 7 (NLP7), which has been previously reported to play a role in resistance to adverse environments. In summary, our findings suggest that among the BrAS2 gene family, BrAS2-47 and BrAS2-10 have the most potential for the regulation of abiotic stress tolerance. These results will facilitate future functional investigations of BrAS2 genes in B. rapa.

Abiotic Stress in Crop Production

The vast majority of agricultural land undergoes abiotic stress that can significantly reduce agricultural yields. Understanding the mechanisms of plant defenses against stresses and putting this knowledge into practice is, therefore, an integral part of sustainable agriculture. In this review, we focus on current findings in plant resistance to four cardinal abiotic stressors—drought, heat, salinity, and low temperatures. Apart from the description of the newly discovered mechanisms of signaling and resistance to abiotic stress, this review also focuses on the importance of primary and secondary metabolites, including carbohydrates, amino acids, phenolics, and phytohormones. A meta-analysis of transcriptomic studies concerning the model plant Arabidopsis demonstrates the long-observed phenomenon that abiotic stressors induce different signals and effects at the level of gene expression, but genes whose regulation is similar under most stressors can still be traced. The analysis further reveals the transcriptional modulation of Golgi-targeted proteins in response to heat stress. Our analysis also highlights several genes that are similarly regulated under all stress conditions. These genes support the central role of phytohormones in the abiotic stress response, and the importance of some of these in plant resistance has not yet been studied. Finally, this review provides information about the response to abiotic stress in major European crop plants—wheat, sugar beet, maize, potatoes, barley, sunflowers, grapes, rapeseed, tomatoes, and apples.