LoSWEET14, a Sugar Transporter in Lily, Is Regulated by Transcription Factor LoABF2 to Participate in the ABA Signaling Pathway and Enhance Tolerance to Multiple Abiotic Stresses in Tobacco

Identification and characterization of SWEET gene family in passion fruit reveals the involvement of PeSWEET3 in soluble sugar accumulation

The sugars will eventually be exported transporters (SWEET) family is a class of sugar transporters that play crucial roles in plant growth, reproduction, and stresses response. The characteristics of 21 PeSWEETs, identified in passion fruit (Passiflora edulis Sims) and divided into four clades, were evaluated. Structural feature analysis showed that exon numbers ranged from 4 to 12, while motif 1, 2, and 3 were highly conserved. Analysis of RNA-seq from different tissues revealed that PeSWEETs showed tissue-specificity. Additionally, Cis-acting regulatory element analysis indicated that abundant hormone-response and stress response elements were enriched in promoters of PeSWEETs. Exogenous abscisic acid (ABA) treatment led to an increase in the soluble sugar accumulation and up-regulated the expression level of PeSWEET3. The PeSWEET3 protein localizes on the plasma membrane and exhibits transport activity of fructose, glucose, and mannose. Furthermore, ectopic expression of PeSWEET3 significantly enhanced soluble sugar accumulation in leaves of transgenic tobacco. Collectively, these results lay a solid foundation for further exploration on the role of PeSWEETs.

Investigation of wheat cold response pathway regulated by TaICE41 and TaCBFⅣd-B9 through Brachypodium distachyon transformation

Wheat (Triticum aestivum L.), a major global crop, is vulnerable to freezing stress, particularly during late spring frosts. Enhancing freezing tolerance through cold acclimation, primarily via the ICE-CBF-COR pathway, is crucial for improving wheat productivity. This study focuses on identifying genes regulated by the ICE-CBF pathway and those that function independently in response to freezing stress. TaICE41 and TaCBFⅣd-B9, two key genes associated with cold tolerance, were cloned and analyzed for their phylogenetic characteristics and subcellular localization. Transgenic Brachypodium distachyon overexpressing these genes demonstrated enhanced freezing tolerance, with increased survival rates and proline content, compared to wild-type plants. RNA-seq analysis revealed distinct gene expression profiles under cold stress, highlighting both shared and unique pathways regulated by ICE41 and CBF. Notably, the TaICE41-overexpressing lines exhibited upregulation of genes involved in phenylpropanoid biosynthesis and starch-sucrose metabolism, contributing to stress response. This study provides new insights into the ICE-CBF pathway and its role in cold tolerance, emphasizing the importance of understanding both ICE-CBF-regulated and independent cold-responsive genes for improving freezing tolerance in crops.

Genetic Characterization of SWEET Genes in Coconut Palm

Sugar-Will-Eventually-be-Exported Transporters (SWEETs) play a crucial role in sugar transport in plants, mediating both plant development and stress responses. Despite their importance, there has been limited research characterizing the functional characteristics of CnSWEET genes in coconut (Cocos nucifera). In this study, we conducted a systematic analysis of SWEET genes in coconut using bioinformatics, subcellular localization studies, in silico promoter analysis, and functional assays with yeast mutants. A total of 16 CnSWEET genes were identified and grouped into four clades. Clade I contained the highest number of genes (eight), derived from four pairs of duplicated genomic segments. In contrast, the other clades had fewer genes (one to four) compared to those in Arabidopsis and other species in the Arecaceae family. An extensive analysis of gene expansion using MSCanX indicated significant divergence in gene expansion patterns, both between and within monocots and dicots, as well as among closely related species within the same family. Notable variations in conserved protein motifs and the number of transmembrane helices (TMHs) were detected within Clade I compared to other clades, affecting the subcellular localization of CnSWEET proteins. Specifically, seven TMHs were associated with proteins located in the cell membrane, while CnSWEET2A, which had five TMHs, was found in both the cell membrane and cytosol. Promoter analysis revealed that some CnSWEET genes contained endosperm or seed specific motifs associated with specific endosperm expression, consistent with expression patterns observed in transcriptome data. Functional analysis of five CnSWEET genes, with transcript sequences supported by transcriptome data, was conducted using yeast mutant complementation assays. This analysis demonstrated diverse transport activities for sucrose, fructose, glucose, galactose, and mannose. Our findings provide valuable insights into the functional diversity of SWEET genes in coconuts and their potential roles in stress responses and plant development.

Transcription factor ZjABF1 promotes sugar accumulation and abiotic resistance by positively regulating the expression of sugar transport protein ZjSWEET11 and ZjSWEET18 in Chinese jujube

Chinese jujube (Ziziphus jujuba Mill.) exhibits a remarkable resilience to both drought and salinity. Additionally, it is characterized by a high sugar content, with sucrose being the predominant component of its soluble sugars. However, the molecular mechanisms linking robust abiotic stress resistance, sugar accumulation and sugar transport proteins ZjSWEETs remain poorly understood in jujube. In this study, we identified two critical sugar transport proteins, ZjSWEET11 and ZjSWEET18, in Chinese jujube through comprehensive assays and established a positive correlation between sucrose accumulation and the expression of these genes. Furthermore, we discovered that the key transcription factor ZjABF1 within the ABA signaling pathway positively regulated the transcriptional expression of ZjSWEET11 and ZjSWEET18 and increased the sugar contents, consequently improving the drought and salt stress resistance of plants. Basing on these results, we proposed a working module that ZjABF1 promotes sugar accumulation and improves stress resistance by targeting and up-regulating of ZjSWEET11 and ZjSWEET18. Our findings provide valuable insights into the mechanisms underlying sugar accumulation and abiotic stress adaptation in Chinese jujube.

The transcription factors ERF105 and NAC72 regulate expression of a sugar transporter gene and hexose accumulation in grape

Sugar transport plays a pivotal role in determining the productivity of plants and their capacity to act as carbon sinks. In the major fruit crop grapevine (Vitis vinifera L.), the transporter gene V. vinifera Sugars Will Eventually be Exported Transporter 15 (VvSWEET15) is strongly expressed during berry ripening. However, the specific functions of VvSWEET15 and the mechanisms governing its transcriptional regulation remain largely unresolved. Here, we demonstrate that VvSWEET15 functions as a hexose transporter whose expression is associated with the strong sugar accumulation that starts at the véraison stage. We also characterize VvERF105 as a repressor that binds to the LTR-binding element in the VvSWEET15 promoter, thereby downregulating its expression and inhibiting hexose accumulation at the prevéraison stage. In contrast, VvNAC72 is an activator that binds to the VvNAC72-binding domain (CACATG) and promotes VvSWEET15 expression and hexose accumulation at postvéraison stages. Both transcription factors and VvSWEET15 are preferentially expressed in phloem cells. These results demonstrate that the balance between transcriptional activators and repressors is critical in regulating VvSWEET15 expression in sink organs. Further understanding of these processes will help improve plant productivity and their potential to be used as carbon sinks.

TaCDPK1-5A positively regulates drought response through modulating osmotic stress responsive-associated processes in wheat (Triticum aestivum)

KEY MESSAGE

Wheat TaCDPK1-5A plays critical roles in mediating drought tolerance through regulating osmotic stress-associated physiological processes. Calcium (Ca2+) acts as an essential second messenger in plant signaling pathways and impacts plant abiotic stress responses. This study reported the function of TaCDPK1-5A, a calcium-dependent protein kinase (CDPK) gene in T. aestivum, in mediating drought tolerance. TaCDPK1-5A sensitively responded to drought and exogenous abscisic acid (ABA) signaling, displaying induced transcripts in plants under drought and ABA treatments. Yeast two-hybrid and co-immunoprecipitation assays revealed that TaCDPK1-5A interacts with the mitogen-activated protein kinase TaMAPK4-7D whereas the latter with ABF transcription factor TaABF1-3A, suggesting that TaCDPK1-5A constitutes a signaling module with above partners to transduce signals initiated by drought/ABA stressors. Overexpression of TaCDPK1-5A, TaMAPK4-7D and TaABF1-3A enhanced plant drought adaptation by modulating the osmotic stress-related physiological indices, including increased osmolyte contents, enlarged root morphology, and promoted stomata closure. Yeast one-hybrid assays indicated the binding ability of TaABF1-3A with promoters of TaP5CS1-1B, TaPIN3-5A, and TaSLAC1-3-2A, the genes encoding P5CS enzyme, PIN-FORMED protein, and slow anion channel, respectively. ChIP-PCR and transcriptional activation assays confirmed that TaABF1-3A regulates these genes at transcriptional level. Moreover, transgene analysis indicated that these stress-responsive genes positively regulated proline biosynthesis (TaP5CS1-1B), root morphology (TaPIN3-5A), and stomata closing (TaSLAC1-3-2A) upon drought signaling. Positive correlations were observed between yield and the transcripts of TaCDPK1-5A signaling partners in wheat cultivars under drought condition, with haplotype TaCDPK1-5A-Hap1 contributing to improved drought tolerance. Our study concluded that TaCDPK1-5A positively regulates drought adaptation and is a valuable target for molecular breeding the drought-tolerant cultivars in T. aestivum.

From acidity to sweetness: a comprehensive review of carbon accumulation in grape berries

Most of the carbon found in fruits at harvest is imported by the phloem. Imported carbon provide the material needed for the accumulation of sugars, organic acids, secondary compounds, in addition to the material needed for the synthesis of cell walls. The accumulation of sugars during fruit development influences not only sweetness but also various parameters controlling fruit composition (fruit "quality"). The accumulation of organic acids and sugar in grape berry flesh cells is a key process for berry development and ripening. The present review presents an update of the research on grape berry development, anatomical structure, sugar and acid metabolism, sugar transporters, and regulatory factors.

Identification and Characterization of the AREB/ABF Gene Family in Three Orchid Species and Functional Analysis of DcaABI5 in Arabidopsis

AREB/ABF (ABA response element binding) proteins in plants are essential for stress responses, while our understanding of AREB/ABFs from orchid species, important traditional medicinal and ornamental plants, is limited. Here, twelve AREB/ABF genes were identified within three orchids' complete genomes and classified into three groups through phylogenetic analysis, which was further supported with a combined analysis of their conserved motifs and gene structures. The cis-element analysis revealed that hormone response elements as well as light and stress response elements were widely rich in the AREB/ABFs. A prediction analysis of the orchid ABRE/ABF-mediated regulatory network was further constructed through cis-regulatory element (CRE) analysis of their promoter regions. And it revealed that several dominant transcriptional factor (TF) gene families were abundant as potential regulators of these orchid AREB/ABFs. Expression profile analysis using public transcriptomic data suggested that most AREB/ABF genes have distinct tissue-specific expression patterns in orchid plants. Additionally, DcaABI5 as a homolog of ABA INSENSITIVE 5 (ABI5) from Arabidopsis was selected for further analysis. The results showed that transgenic Arabidopsis overexpressing DcaABI5 could rescue the ABA-insensitive phenotype in the mutant abi5. Collectively, these findings will provide valuable information on AREB/ABF genes in orchids.