ScAREB4 promotes potato constitutive and acclimated freezing tolerance associated with enhancing trehalose synthesis and oxidative stress tolerance

General control nonderepressible 4 activates the transcription of trehalose phosphorylase to improve trehalose production and abiotic stress tolerance in Ganoderma lucidum

Trehalose plays an important role in enhancing abiotic stress tolerance. Although studies have reported the induction of trehalose by adverse environments, the molecular mechanism underlying its induction in fungi is unclear. In fungi, the trehalose phosphorylase (TreP) catalyzes the reversible reaction of trehalose formation. Here, we found that the carbon and nitrogen metabolism integrated transcription factor, general control nonderepressible 4 (GCN4) directly binds to the promoter of TreP in Ganoderma lucidum. GCN4 up-regulates the transcription and protein levels of TreP, leading to enhanced trehalose synthase activity and trehalose accumulation. A reduced abundance of GCN4 alleviated the low-nitrogen induced increase in Trep and trehalose contents. As a result, knockdown of both GCN4 and TreP leads to a reduction in the trehalose content and growth inhibition of mycelia, especially under low-nitrogen conditions. Furthermore, in addition to nitrogen deficiency, both high temperature and drought treatments increase the transcription and protein levels of GCN4 and TreP. The GCN4 or TreP knockdown strains are hypersensitive to heat stress and drought, while exogenous trehalose treatment enhances the mycelial growth under stressful conditions. Together, our results revealed that the GCN4-TreP module promotes trehalose accumulation in response to abiotic stresses to improve the stress tolerance of G. lucidum, and highlighted the pivotal role of GCN4 in integrating metabolic adaptation to environmental stresses.

An integrative overview of cold response and regulatory pathways in horticultural crops

Global climate change challenges agricultural production, as extreme temperature fluctuations negatively affect crop growth and yield. Low temperature (LT) stress impedes photosynthesis, disrupts metabolic processes, and compromises the integrity of cell membranes, ultimately resulting in diminished yield and quality. Notably, many tropical or subtropical horticultural plants are particularly susceptible to LT stress. To address these challenges, it is imperative to understand the mechanisms underlying cold tolerance in horticultural crops. This review summarizes recent advances in the physiological and molecular mechanisms that enable horticultural crops to withstand LT stress, emphasizing discrepancies between horticultural crops and model systems. These mechanisms include C-repeat binding factor-dependent transcriptional regulation, post-translational modifications, epigenetic control, and metabolic regulation. Reactive oxygen species, plant hormones, and light signaling pathways are integrated into the cold response network. Furthermore, technical advances for improving cold tolerance are highlighted, including genetic improvement, the application of light-emitting diodes, the utility of novel plant growth regulators, and grafting. Finally, prospective directions for fundamental research and practical applications to boost cold tolerance are discussed.

Comprehensive transcriptome analysis reveals StMAPK7 regulate cold response in potato

Cultivated potato (Solanum tuberosum L.) is an important tuber crop in the world. Cold stress adversely affects productivity and quality of potato. However, the molecular mechanism underlying the cold stress responses remains unclear in potato. The chloroplast ultrastructure of S. cardiophyllum in non-acclimated and cold acclimation plants under -2 °C for 6 h contained fewer thylakoid membranes, more spherical than those in 0 h (control, non-acclimated). The chloroplast ultrastructure of S. commersonii in non-acclimated and cold acclimation plants under -2 °C 6 h were similar to the non-cold stress. RNA sequencing (RNA-seq) analysis showed that 3,623 DEGs (differentially expressed genes) were detected in the S. commersonii and S. cardiophyllum with or without cold acclimation. GO analysis revealed that the membrane protein complex, photosynthesis and molecular function regulator were enriched terms in three category of S. commersonii and S. cardiophyllum. KEGG analysis found that genes were enriched to photosynthesis and chlorophyll metabolism. A total of 27 distinct modules were identified by weighted gene co-expression network analysis, four regulatory networks contained cold related genes were constructed. The StMAPK7 were differently expressed in S. cardiophyllum. Subcellular location studies showed that the StMAPK7 protein is mainly localized to the nucleus in tobacco. Overexpression of StMAPK7 exhibited lower electrolyte leakage and less leaves injury area than that of wild type, indicating StMAPK7 positively regulates cold stress in potato. These findings would provide fundamental insight into the cold stress response regulatory networks and supply a theoretical basis for breeding cold-resistant potato cultivars.

The transcription factor WRKY41-FLAVONOID 3'-HYDROXYLASE module fine-tunes flavonoid metabolism and cold tolerance in potato

Cold stress adversely affects crop growth and productivity. Resolving the genetic basis of freezing tolerance is important for crop improvement. Wild potato (Solanum commersonii) exhibits excellent freezing tolerance. However, the genetic factors underlying its freezing tolerance remain poorly understood. Here, we identified flavonoid 3'-hydroxylase (F3'H), a key gene in the flavonoid biosynthesis pathway, as highly expressed in S. commersonii compared with cultivated potato (S. tuberosum L.). Loss of ScF3'H function impaired freezing tolerance in S. commersonii, while ScF3'H overexpression in cultivated potato enhanced its freezing tolerance. Metabolic analysis revealed that F3'H generates more downstream products by adding hydroxyl (-OH) groups to the flavonoid ring structures. These flavonoids enhance reactive oxygen species scavenging, thereby contributing to freezing tolerance. Furthermore, the W-box element in the F3'H promoter plays a critical role in cold responses. Cold-induced transcription factor ScWRKY41 directly binds to the ScF3'H promoter region and recruits histone acetyltransferase 1 (ScHAC1), which enhances histone acetylation at the F3'H locus and activates its transcription. Overall, we identified the cold-responsive WRKY41-F3'H module that enhances freezing tolerance by augmenting the antioxidant capacity of flavonoids. This study reveals a valuable natural gene module for breeding enhanced freezing tolerance in potato and other crops.

Genome-Wide Identification and Expression Divergence of CBF Family in Actinidia arguta and Functional Analysis of AaCBF4 Under Cold Stress

The C-repeat binding factors (CBFs) gene is essential for plants' cold response, which could not only be induced by the inducer of CBF expression (ICE) genes but also activated the expression of the cold-regulated (COR) gene, thereby participating in the ICE-CBF-COR cold response pathway. However, this gene family and its functions in Actinidia arguta remain unclear. In this study, whole-genome identification and functional analysis of CBF family members in A. arguta were performed. Eighteen CBF genes, which were located on four chromosomes and had five tandem repeats, were identified. The proteins encoded by the genes were predicted to be located in the nucleus and cytoplasm. The results of the promoter cis-acting element analysis revealed light response elements, low-temperature response elements, and hormone (methyl jasmonate, gibberellin, salicylic acid, etc.) response elements. We analyzed collinearity with other kiwifruit genomes, and, interestingly, the number of CBF family members differed across geographic locations of A. arguta. RT-qPCR revealed that the expression of the CBF gene family differed under low-temperature treatment; specifically, we observed differences in the expression of all the genes. Based on phylogenetic relationships and RT-qPCR analysis, the expression of AaCBF4.1 (AaCBF4) was found to be highly upregulated, and the function of this gene in cold resistance was further verified via overexpression in transgenic Arabidopsis. AaCBF4-overexpressing plants showed higher tolerance to cold stress, showing a higher germination rate, higher chlorophyll content and lower relative electrolyte leakage. In addition, compared with the wild-type Arabidopsis, the overexpressing plants exhibited significantly reduced oxidative damage due to the reduction in reactive oxygen species production under cold stress. Therefore, AaCBF4 plays an important role in improving the cold resistance of Actinidia arguta and can be further used to develop kiwifruit germplasm resources with strong cold resistance.

In silico analysis of trehalose biosynthesis genes provides clues to reveal its roles in Avicennia marina adaptation to tidal submergence

Trehalose has an important function for alleviating various abiotic stress in plants. Nevertheless, the functional and evolutionary characteristics of trehalose biosynthesis genes in mangrove plants is not documented. Here, using typical mangrove Avicennia marina, we found the trehalose content decreased in the roots and leaves and T6P increased significantly in the leaves under tidal submergence. Then, the basic physicochemical properties and gene structure of trehalose biosynthesis genes (AmTPS and AmTPP), and the conserved domain and motifs of AmTPS and AmTPP proteins were analyzed. The collinearity analysis and Ka/Ks values indicated that AmTPS and AmTPP are evolutionarily conserved. Tissue-specific expression profiling showed that most AmTPS and AmTPP genes have tissue specificity. RNA-Seq analysis showed that five AmTPS genes were markedly up-regulated in A. marina treated with tidal submergence. Subcellular localization analysis revealed three genes including AmTPS10B, AmTPS11A and AmTPS11C out of these five up-regulated AmTPS genes work in plasma membrane, cytoplasm and nucleus. Finally, integrative analysis of bioinformatics and RNA-Seq analysis were performed to excavate transcription factors that may regulate AmTPS and AmTPP genes in A. marina response to submergence. Taken together, these findings provide new insights into the response to tidal submergence in A. marina at the aspect of trehalose.

Genome-Wide Analysis of the Phospholipase Ds in Perennial Ryegrass Highlights LpABFs-LpPLDδ3 Cascade Modulated Osmotic and Heat Stress Responses

The phospholipase Ds (PLDs) are crucial for cellular signalling and play roles in plant abiotic stress response. In this study, we identified 12 PLD genes from the genome data of perennial ryegrass (Lolium perenne), which is widely used as forage and turfgrass. Among them, LpPLDδ3 was significantly repressed by ABA treatment, and induced by drought stress and heat stress treatments. The ectopic overexpression (OE) of LpPLDδ3 in Arabidopsis enhanced plant tolerance to osmotic and heat stress as demonstrated by an increased survival rate and reduced malondialdehyde (MDA) accumulation and electrolyte leakage (EL). Arabidopsis endogenous ABA RESPONSIVE ELEMENT BINDING FACTORs (ABFs) and heat stress responsive genes were elevated in LpPLDδ3 OE lines under osmotic and heat stress treatments. Additionally, overexpression of LpPLDδ3 in perennial ryegrass protoplasts could increase heat stress tolerance and elevate expression level of heat stress responsive genes. Moreover, LpABF2 and LpABF4 depressed the LpPLDδ3 expression by directly binding to its ABRE core-binding motif of promoter region. In summary, LpPLDδ3 was repressed by LpABF2 and LpABF4 and positively involved in perennial ryegrass osmotic and heat stress responses.

Overexpression of StBBX14 Enhances Cold Tolerance in Potato

Potato (Solanum tuberosum L.) is an important food crop, but low temperature affects the potato growth and yield. In this study, the expression level of StBBX14 was significantly increased over 1 h and then gradually decreased under cold stress. The subcellular localization of the StBBX14 protein took place in the nucleus. The OE-StBBX14 transgenic lines showed less leaf damage and significantly lower electrolyte leakage compared with the WT under cold stress, indicating that the overexpression of StBBX14 in the potato enhanced the cold resistance. A transcriptome analysis showed that a total of 2449 and 6274 differentially expressed genes were identified in WT-1 h and WT-12 h, respectively, when compared with WT-0h. A Gene Ontology enrichment analysis revealed that photosynthesis, cell wall, thylakoid, transcription regulator activity, oxidoreductase activity and glucosyltransferase activity were significantly enriched in OE-StBBX14 and WT. A total of 14 distinct modules were generated by a WGCNA analysis based on all differentially expressed genes (DEGs). Four major modules with cold-related genes were isolated. RT-qPCR analysis showed that the expression patterns of eight DEGs were consistent between the qPCR and RNA-seq. These findings illustrate that the StBBX14 played an important role in cold stress in potato and provided a data basis for the genetic improvement of cold resistance traits of potato.

Understanding cold stress response mechanisms in plants: an overview

Low-temperature stress significantly impacts plant growth, development, yield, and geographical distribution. However, during the long-term process of evolution, plants have evolved complicated mechanisms to resist low-temperature stress. The cold tolerance trait is regulated by multiple pathways, such as the Ca2+ signaling cascade, mitogen-activated protein kinase (MAPK) cascade, inducer of CBF expression 1 (ICE1)-C-repeat binding factor (CBF)-cold-reulated gene (COR) transcriptional cascade, reactive oxygen species (ROS) homeostasis regulation, and plant hormone signaling. However, the specific responses of these pathways to cold stress and their interactions are not fully understood. This review summarizes the response mechanisms of plants to cold stress from four aspects, including cold signal perception and transduction, ICE1-CBF-COR transcription cascade regulation, ROS homeostasis regulation and plant hormone signal regulation. It also elucidates the mechanism of cold stress perception and Ca2+ signal transduction in plants, and proposes the important roles of transcription factors (TFs), post-translational modifications (PTMs), light signals, circadian clock factors, and interaction proteins in the ICE1-CBF-COR transcription cascade. Additionally, we analyze the importance of ROS homeostasis and plant hormone signaling pathways in plant cold stress response, and explore the cross interconnections among the ICE1-CBF-COR cascade, ROS homeostasis, and plant hormone signaling. This comprehensive review enhances our understanding of the mechanism of plant cold tolerance and provides a molecular basis for genetic strategies to improve plant cold tolerance.

MsMIOX2, encoding a MsbZIP53-activated myo-inositol oxygenase, enhances saline-alkali stress tolerance by regulating cell wall pectin and hemicellulose biosynthesis in alfalfa

Alfalfa is one of the most widely cultivated forage crops worldwide. However, soil salinization restricts alfalfa growth and development and affects global productivity. The plant cell wall is the first barrier against various stresses. Therefore, elucidating the alterations in cell wall architecture is crucial for stress adaptation. This study aimed to clarify the impact of myo-inositol oxygenase 2 (MsMIOX2) on cell wall pectin and hemicellulose biosynthesis under saline-alkali stress and identify the upstream transcription factors that govern MsMIOX2. MsMIOX2 activation induced cell wall pectin and hemicellulose accumulation under saline-alkali stress. The effects of MsMIOX2 in saline-alkali tolerance were investigated by characterizing its overexpression and RNA interference lines. MsMIOX2 overexpression positively regulated the antioxidant system and photosynthesis in alfalfa under saline-alkali stress. MsMIOX2 exhibited myo-inositol oxygenase activity, which increased polysaccharide contents, facilitated pectin and hemicellulose biosynthesis, and extended the cell wall thickness. However, MsMIOX2 RNA interference decreased cell wall thickness and alleviated alfalfa saline-alkali stress tolerance. In addition, MsbZIP53 was identified as an upstream transcriptional MsMIOX2 regulator by yeast one-hybrid, electrophoretic mobility shift assay, dual-luciferase, and beta-glucuronidase assays. MsbZIP53 overexpression increased MsMIOX2 expression, elevated MIOX activity, reinforced the antioxidant system and photosynthesis, and increased saline-alkali stress tolerance in alfalfa. In conclusion, this study presents a novel perspective for elucidating the molecular mechanisms of saline-alkali stress tolerance in alfalfa and emphasizes the potential use of MsMIOX2 in alfalfa breeding.

Trehalose along with ABA promotes the salt tolerance of Avicennia marina by regulating Na+ transport

Mangroves grow in tropical/subtropical intertidal habitats with extremely high salt tolerance. Trehalose and trehalose-6-phosphate (T6P) have an alleviating function against abiotic stress. However, the roles of trehalose in the salt tolerance of salt-secreting mangrove Avicennia marina is not documented. Here, we found that trehalose was significantly accumulated in A. marina under salt treatment. Furthermore, exogenous trehalose can enhance salt tolerance by promoting the Na+ efflux from leaf salt gland and root to reduce the Na+ content in root and leaf. Subsequently, eighteen trehalose-6-phosphate synthase (AmTPS) and 11 trehalose-6-phosphate phosphatase (AmTPP) genes were identified from A. marina genome. Abscisic acid (ABA) responsive elements were predicted in AmTPS and AmTPP promoters by cis-acting elements analysis. We further identified AmTPS9A, as an important positive regulator, that increased the salt tolerance of AmTPS9A-overexpressing Arabidopsis thaliana by altering the expressions of ion transport genes and mediating Na+ efflux from the roots of transgenic A. thaliana under NaCl treatments. In addition, we also found that ABA could promote the accumulation of trehalose, and the application of exogenous trehalose significantly promoted the biosynthesis of ABA in both roots and leaves of A. marina. Ultimately, we confirmed that AmABF2 directly binds to the AmTPS9A promoter in vitro and in vivo. Taken together, we speculated that there was a positive feedback loop between trehalose and ABA in regulating the salt tolerance of A. marina. These findings provide new understanding to the salt tolerance of A. marina in adapting to high saline environment at trehalose and ABA aspects.

Haplotype-resolved genome and mapping of freezing tolerance in the wild potato Solanum commersonii

Solanum commersonii (2n = 2x = 24, 1EBN, Endosperm Balance Number), native to the southern regions of Brazil, Uruguay, and northeastern Argentina, is the first wild potato germplasm collected by botanists and exhibits a remarkable array of traits related to disease resistance and stress tolerance. In this study, we present a high-quality haplotype-resolved genome of S. commersonii. The two identified haplotypes demonstrate chromosome sizes of 706.48 and 711.55 Mb, respectively, with corresponding chromosome anchoring rates of 94.2 and 96.9%. Additionally, the contig N50 lengths are documented at 50.87 and 45.16 Mb. The gene annotation outcomes indicate that the haplotypes encompasses a gene count of 39 799 and 40 078, respectively. The genome contiguity, completeness, and accuracy assessments collectively indicate that the current assembly has produced a high-quality genome of S. commersonii. Evolutionary analysis revealed significant positive selection acting on certain disease resistance genes, stress response genes, and environmentally adaptive genes during the evolutionary process of S. commersonii. These genes may be related to the formation of diverse and superior germplasm resources in the wild potato species S. commersonii. Furthermore, we utilized a hybrid population of S. commersonii and S. verrucosum to conduct the mapping of potato freezing tolerance genes. By combining BSA-seq analysis with traditional QTL mapping, we successfully mapped the potato freezing tolerance genes to a specific region on Chr07, spanning 1.25 Mb, with a phenotypic contribution rate of 18.81%. In short, current research provides a haplotype-resolved reference genome of the diploid wild potato species S. commersonii and establishes a foundation for further cloning and unraveling the mechanisms underlying cold tolerance in potatoes.

Integrated analysis of ATAC-seq and transcriptomic reveals the ScDof3-ScproC molecular module regulating the cold acclimation capacity of potato

Low temperature severely affects the geographical distribution and production of potato, which may incur cold damage in early spring or winter. Cultivated potatoes, mainly derived from Solanum tuberosum, are sensitive to freezing stress, but wild species of potato such as S. commersonii exhibit both constitutive freezing tolerance and/or cold acclimation tolerance. Hence, such wild species could assist in cold hardiness breeding. Yet the key transcription factors and their downstream functional genes that confer freezing tolerance are far from clear, hindering the breeding process. Here, we used ATAC-seq (Assay for Transposase-Accessible Chromatin with high-throughput sequencing) alongside RNA-seq to investigate the variation in chromatin accessibility and patterns of gene expression in freezing-tolerant CMM5 (S. commersonii), before and after its cold treatment. Our results suggest that after exposure to cold, transcription factors including Dof3, ABF2, PIF4, and MYB4 were predicted to further control the genes active in the synthetic/metabolic pathways of plant hormones, namely abscisic acid, polyamine, and reductive glutathione (among others). This suggests these transcription factors could regulate freezing tolerance of CMM5 leaves. In particular, ScDof3 was proven to regulate the expression of ScproC (pyrroline-5-carboxylate reductase, P5CR) according to dual-LUC assays. Overexpressing ScDof3 in Nicotiana benthamiana leaves led to an increase in both the proline content and expression level of NbproC (homolog of ScproC). These results demonstrate the ScDof3-ScproC module regulates the proline content and thus promotes freezing tolerance in potato. Our research provides valuable genetic resources to further study the molecular mechanisms underpinning cold tolerance in potato.

Genome-Wide Identification and Expression Analysis of the Trehalose-6-phosphate Synthase and Trehalose-6-phosphate Phosphatase Gene Families in Rose (Rosa hybrida cv 'Carola') under Different Light Conditions

Trehalose, trehalose-6-phosphate synthase (TPS),and trehalose-6-phosphatase (TPP) have been reported to play important roles in plant abiotic stress and growth development. However, their functions in the flowering process of Rosa hybrida have not been characterized. In this study we found that, under a short photoperiod or weak light intensity, the content of trehalose in the shoot apical meristem of Rosa hybrida cv 'Carola' significantly decreased, leading to delayed flowering time. A total of nine RhTPSs and seven RhTPPs genes were identified in the genome. Cis-element analysis suggested that RhTPS and RhTPP genes were involved in plant hormones and environmental stress responses. Transcriptome data analysis reveals significant differences in the expression levels of RhTPSs and RhTPPs family genes in different tissues and indicates that RhTPPF and RhTPPJ are potential key genes involved in rose flower bud development under different light environments. The results of quantitative real-time reverse transcription (qRT-PCR) further indicate that under short photoperiod and weak light intensity all RhTPP members were significantly down-regulated. Additionally, RhTPS1a, RhTPS10, and RhTPS11 were up-regulated under a short photoperiod and showed a negative correlation with flowering time and trehalose content decrease. Under weak light intensity, RhTPS11 was up-regulated and negatively regulated flowering, while RhTPS5, RhTPS6, RhTPS7b, RhTPS9, and RhTPS10 were down-regulated and positively regulated flowering. This work lays the foundation for revealing the functions of RhTPS and RhTPP gene families in the regulation of rose trehalose.