A novel plant growth regulator B2 mediates drought resistance by regulating reactive oxygen species, phytohormone signaling, phenylpropanoid biosynthesis, and starch metabolism pathways in Carex breviculmis.

Drought is one of the most common environmental stressors that severely threatens plant growth, development, and productivity. B2 (2,4-dichloroformamide cyclopropane acid), a novel plant growth regulator, plays an essential role in drought adaptation, significantly enhancing the tolerance of Carex breviculmis seedlings. Its beneficial effects include improved ornamental value, sustained chlorophyll content, increased leaf dry weight, elevated relative water content, and enhanced root activity under drought conditions. B2 also directly scavenges hydrogen peroxide and superoxide anion contents while indirectly enhancing the activities of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) to detoxify reactive oxygen species (ROS) oxidative damage. Transcriptome analysis demonstrated that B2 activates drought-responsive transcription factors (AP2/ERF-ERF, WRKY, and mTERF), leading to significant upregulation of genes associated with phenylpropanoid biosynthesis (HCT, POD, and COMT). Additionally, these transcription factors were found to suppress the degradation of starch. B2 regulates phytohormone signaling related-genes, leading to an increase in abscisic acid contents in drought-stressed plants. Collectively, these findings offer new insights into the intricate mechanisms underlying C. breviculmis' resistance to drought damage, highlighting the potential application of B2 for future turfgrass establishment and management with enhanced drought tolerance.

Melatonin-Mediated Enhancement of Photosynthetic Capacity and Photoprotection Improves Salt Tolerance in Wheat.

The role of melatonin in plant growth and response to environmental stress has been widely demonstrated. However, the physiological and molecular regulation of salt tolerance in wheat seedlings by melatonin remains unclear. In this study, we investigated changes in phenotype, physiology, photosynthetic parameters, and transcript levels in wheat seedlings to reveal the role of melatonin in the regulation of salt tolerance in wheat. The results indicate that the application of exogenous melatonin significantly alleviates growth inhibition, reactive oxygen species accumulation, and membrane oxidative damage induced by salt stress in wheat. Additionally, exogenous melatonin increased antioxidant enzyme activity and regulated photosynthetic gas exchange. Transcriptomic data showed a significant up-regulation of genes encoding light-harvesting chlorophyll protein complex proteins in photosynthesis and genes related to chlorophyll and carotenoid biosynthesis under the influence of melatonin. These results suggest that exogenous melatonin improves salt tolerance in wheat seedlings by enhancing the antioxidant, photoprotective, and photosynthesis activities.

Integrative analysis of transcriptome, proteome, and ubiquitome changes during rose petal abscission.

Plant organ abscission is regulated by multiple physiological and biochemical processes. However, the transcriptional, translational, and post-translational modifications occurring during organ abscission have not been systematically investigated. In this study, we report transcriptome, proteome, and ubiquitome data for the abscission zone (AZ) of rose petals collected during petal shedding. We quantified 40,506 genes, 6,595 proteins, and 2,720 ubiquitinated proteins in rose petal AZ. Our results showed that during petal abscission, 1,496 genes were upregulated and 2,199 were downregulated; 271 proteins were upregulated and 444 were downregulated; and 139 ubiquitination sites in 100 proteins were upregulated and 55 ubiquitination sites in 48 proteins were downregulated. Extracellular levels of cell component proteins were significantly increased, while levels within protoplasts were significantly decreased. During petal abscission, transcript levels of genes involved in defense response, transport, and metabolism changed significantly. Levels of proteins involved in the starch and sucrose metabolism and phenylpropanoid biosynthesis pathways were significantly altered at both the transcript and protein levels. The transcriptional and translational upregulation of peroxidase (POD), in the phenylpropanoid biosynthesis, pathway may be associated with deposition of lignin, which forms a protective layer during petal abscission. Overall, our data provide a comprehensive assessment of the translational and post-translational changes that occur during rose petal abscission.

Coronatine Enhances Chilling Tolerance of Tomato Plants by Inducing Chilling-Related Epigenetic Adaptations and Transcriptional Reprogramming.

Low temperature is an important environmental factor limiting the widespread planting of tropical and subtropical crops. The application of plant regulator coronatine, which is an analog of Jasmonic acid (JA), is an effective approach to enhancing crop's resistance to chilling stress and other abiotic stresses. However, the function and mechanism of coronatine in promoting chilling resistance of tomato is unknown. In this study, coronatine treatment was demonstrated to significantly increase tomato chilling tolerance. Coronatine increases H3K4me3 modifications to make greater chromatin accessibility in multiple chilling-activated genes. Corresponding to that, the expression of CBFs, other chilling-responsive transcription factor (TF) genes, and JA-responsive genes is significantly induced by coronatine to trigger an extensive transcriptional reprogramming, thus resulting in a comprehensive chilling adaptation. These results indicate that coronatine enhances the chilling tolerance of tomato plants by inducing epigenetic adaptations and transcriptional reprogramming.

Disruption of transcription factor RhMYB123 causes the transformation of stamen to malformed petal in rose (Rosa hybrida).

KEY MESSAGE: We find that the R2R3 MYB transcription factor RhMYB123 has a novel function to regulate stamen-petal organ specification in rose. Rose is one of the ornamental plants with economic importance worldwide. Malformed flower seriously affects the ornamental value and fertility of rose. However, the regulatory mechanism is largely unknown. In this work, we identified a R2R3 MYB transcription factor RhMYB123 from rose, the expression of which significantly decreased from flower differentiation stage to floral organ development stage. Phylogenetic analysis indicated that it belongs to the same subgroup as MYB123 of Arabidopsis and located in nucleus. In addition, RhMYB123 was confirmed to have transcriptional activation function by dual luciferase assay. Silencing RhMYB123 using Virus-Induced Gene Silencing (VIGS) in rose could increase the number of malformed petaloid stamen. Furthermore, we identified 549 differential expressed genes (DEGs) in TRV-RhMYB123 lines compared to TRV controls by RNA-seq of floral buds (flower differentiation stage). Among of those genes, expression of 3 MADS box family genes related to floral organ development reduced in TRV-RhMYB123 lines, including AGAMOUS (RhAG), AGAMOUS LIKE 15 (RhAGL15), and SHATTERPROOF 1 (RhSHP1). Given, previous studies have shown that auxin plays a crucial role in floral meristem initiation and stamen-petal organ specification. We also found 6 DEGs were involved in auxin signal transduction, of which five were reduced expression in TRV-RhMYB123. Taken together, our findings suggested that RhMYB123 may govern the development of malformed petaloid stamen by regulating the expressions of some MADS box family members and auxin signaling pathway elements.

Exogenous Melatonin Improves Seed Germination of Wheat (Triticum aestivum L.) under Salt Stress.

Melatonin (MT) can effectively reduce oxidative damage induced by abiotic stresses such as salt in plants. However, the effects of MT on physiological responses and molecular regulation during wheat germination remains largely elusive. In this study, the response of wheat seeds to MT under salt stress during germination was investigated at physiological and transcriptome levels. Our results revealed that application of MT significantly reduced the negative influence of salt stress on wheat seed germination. The oxidative load was reduced by inducing high activities of antioxidant enzymes. In parallel, the content of gibberellin A3 (GA3) and jasmonic acid (JA) increased in MT-treated seedling. RNA-seq analysis demonstrated that MT alters oxidoreductase activity and phytohormone-dependent signal transduction pathways under salt stress. Weighted correlation network analysis (WGCNA) revealed that MT participates in enhanced energy metabolism and protected seeds via maintained cell morphology under salt stress during wheat seed germination. Our findings provide a conceptual basis of the MT-mediated regulatory mechanism in plant adaptation to salt stress, and identify the potential candidate genes for salt-tolerant wheat molecular breeding.

Integration of Metabolome and Transcriptome Studies Reveals Flavonoids, Abscisic Acid, and Nitric Oxide Comodulating the Freezing Tolerance in Liriope spicata.

Liriope spicata is an evergreen perennial ornamental groundcover with a strong freezing tolerance. However, the molecular mechanism underlying the freezing tolerance in L. spicata remains unclear. In this study, a comprehensive investigation of L. spicata freezing tolerance was conducted at the levels of physiology and biochemistry, metabolite, and transcript during the stress treatment. There were 581 unique differentially expressed metabolites (DEMs) and 10,444 unique differentially expressed genes (DEGs) between freezing treatment and normal cultured plant in leaves. Integrated analysis of metabolomics and transcriptomics showed that flavonoid biosynthesis, carbohydrate metabolism, amino acid metabolism, lipid metabolism, and signal transduction pathways were prominently enriched in response to the freezing stress in L. spicata. Now, we identified genes and metabolites involved in the flavonoid pathway, abscisic acid (ABA) biosynthesis, and the oxidative synthesis pathway of nitric oxide (NO), which may form a regulatory network and play a synergistic effect in osmotic adjustment, reactive oxygen species (ROS) homeostasis, and stomatal closure under freezing stress. These results offer a comprehensive network of flavonoids, ABA, and NO comodulating the freezing tolerance in L. spicata.

Auxin Regulates Sucrose Transport to Repress Petal Abscission in Rose (Rosa hybrida).

Developmental transitions in plants require adequate carbon resources, and organ abscission often occurs due to competition for carbohydrates/assimilates. Physiological studies have indicated that organ abscission may be activated by Suc deprivation; however, an underlying regulatory mechanism that links Suc transport to organ shedding has yet to be identified. Here, we report that transport of Suc and the phytohormone auxin to petals through the phloem of the abscission zone (AZ) decreases during petal abscission in rose (Rosa hybrida), and that auxin regulates Suc transport into the petals. Expression of the Suc transporter RhSUC2 decreased in the AZ during rose petal abscission. Similarly, silencing of RhSUC2 reduced the Suc content in the petals and promotes petal abscission. We established that the auxin signaling protein RhARF7 binds to the promoter of RhSUC2, and that silencing of RhARF7 reduces petal Suc contents and promotes petal abscission. Overexpression of RhSUC2 in the petal AZ restored accelerated petal abscission caused by RhARF7 silencing. Moreover, treatment of rose petals with auxin and Suc delayed ethylene-induced abscission, whereas silencing of RhARF7 and RhSUC2 accelerated ethylene-induced petal abscission. Our results demonstrate that auxin modulates Suc transport during petal abscission, and that this process is regulated by a RhARF7-RhSUC2 module in the AZ.

Rosa hybrida RhERF1 and RhERF4 mediate ethylene- and auxin-regulated petal abscission by influencing pectin degradation.

The timing of plant organ abscission is modulated by the balance of two hormones, ethylene and auxin, while the mechanism of organ shedding depends on the loss of middle lamella pectin in the abscission zone (AZ). However, the mechanisms involved in sensing the balance of auxin and ethylene and that affect pectin degradation during abscission are not well understood. In this study, we identified two members of the APETALA2/ethylene-responsive factor (AP2/ERF) transcription factor family in rose (Rosa hybrida), RhERF1 and RhERF4 which play a role in petal abscission. The expression of RhERF1 and RhERF4 was influenced by ethylene and auxin, respectively. Reduced expression of RhERF1 or RhERF4 was observed to accelerate petal abscission. Global expression analysis and real-time PCR assays revealed that RhERF1 and RhERF4 modulate the expression of genes encoding pectin-metabolizing enzymes. A reduction in the abundance of pectin epitopes was detected in the AZs of RhERF1 and RhERF4-silenced plants by immunofluorescence microscopy analysis. In addition, RhERF1 and RhERF4 were shown to bind to the promoter of the pectin-metabolizing gene ß-GALACTOSIDASE 1 (RhBGLA1), and reduced expression of RhBGLA1 delayed petal abscission. We conclude that during petal abscission, RhERF1 and RhERF4 integrate and coordinate ethylene and auxin signals to modulate pectin metabolism, in part by regulating the expression of RhBGLA1.

Roles of the GA-mediated SPL Gene Family and miR156 in the Floral Development of Chinese Chestnut (Castanea mollissima).

Chestnut (Castanea mollissima) is a deciduous tree species with major economic and ecological value that is widely used in the study of floral development in woody plants due its monoecious and out-of-proportion characteristics. Squamosa promoter-binding protein-like (SPL) is a plant-specific transcription factor that plays an important role in floral development. In this study, a total of 18 SPL genes were identified in the chestnut genome, of which 10 SPL genes have complementary regions of CmmiR156. An analysis of the phylogenetic tree of the squamosa promoter-binding protein (SBP) domains of the SPL genes of Arabidopsis thaliana, Populus trichocarpa, and C. mollissima divided these SPL genes into eight groups. The evolutionary relationship between poplar and chestnut in the same group was similar. A structural analysis of the protein-coding regions (CDSs) showed that the domains have the main function of SBP domains and that other domains also play an important role in determining gene function. The expression patterns of CmmiR156 and CmSPLs in different floral organs of chestnut were analyzed by real-time quantitative PCR. Some CmSPLs with similar structural patterns showed similar expression patterns, indicating that the gene structures determine the synergy of the gene functions. The application of gibberellin (GA) and its inhibitor (Paclobutrazol, PP333) to chestnut trees revealed that these exert a significant effect on the number and length of the male and female chestnut flowers. GA treatment significantly increased CmmiR156 expression and thus significantly decreased the expression of its target gene, CmSPL6/CmSPL9/CmSPL16, during floral bud development. This finding indicates that GA might indirectly affect the expression of some of the SPL target genes through miR156. In addition, RNA ligase-mediated rapid amplification of the 5' cDNA ends (RLM-RACE) experiments revealed that CmmiR156 cleaves CmSPL9 and CmSPL16 at the 10th and 12th bases of the complementary region. These results laid an important foundation for further study of the biological function of CmSPLs in the floral development of C. mollissima.

Transcriptome Profiling of Petal Abscission Zone and Functional Analysis of an Aux/IAA Family Gene RhIAA16 Involved in Petal Shedding in Rose.

Roses are one of the most important cut flowers among ornamental plants. Rose flower longevity is largely dependent on the timing of petal shedding occurrence. To understand the molecular mechanism underlying petal abscission in rose, we performed transcriptome profiling of the petal abscission zone during petal shedding using Illumina technology. We identified a total of 2592 differentially transcribed genes (DTGs) during rose petal shedding. Gene ontology term enrichment and pathway analysis revealed that major biochemical pathways the DTGs were involved in included ethylene biosynthesis, starch degradation, superpathway of cytosolic glycolysis, pyruvate dehydrogenase and TCA cycle, photorespiration and the lactose degradation III pathway. This suggests that alterations in carbon metabolism are an important part of rose petal abscission. Among these DTGs, approximately 150 genes putatively encoding transcription factors were identified in rose abscission zone. These included zinc finger, WRKY, ERF, and Aux/IAA gene families, suggesting that petal abscission involves complex transcriptional reprogramming. Approximately 108 DTGs were related to hormone pathways, of which auxin and ethylene related DTGs were the largest groups including 52 and 41 genes, respectively. These also included 12 DTGs related to gibberellin and 6 DTGs in jasmonic acid pathway. Surprisingly, no DTGs involved in the biosynthesis/signaling of abscisic acid, cytokinin, brassinosteroid, and salicylic acid pathways were detected. Moreover, among DTGs related to auxin, we identified an Aux/IAA gene RhIAA16 that was up-regulated in response to petal shedding. Down-regulation of RhIAA16 by virus-induced gene silencing in rose promoted petal abscission, suggesting that RhIAA16 plays an important role in rose petal abscission.