Lily WRKY factor LlWRKY22 promotes thermotolerance through autoactivation and activation of LlDREB2B

BcWRKY53 promotes chlorophyll biosynthesis and cold tolerance of non-heading Chinese cabbage under cold stress

WRKY transcription factors are widely involved in plant responses to biotic and abiotic stresses, including cold stress. However, they have not been well studied in the regulation of chlorophyll synthesis and cold tolerance. So it is meaningful to analyze the mechanism under cold stress in non-heading Chinese cabbage. Here, BcWRKY53, a transcriptional activator WRKY-III gene, was identified by a screen upstream of the key chlorophyll synthesis genes BcCHLH and BcGUN4. BcWRKY53 was localized in the cell nucleus and induced to a significant extent by cold treatment. Ectopic expression of BcWRKY53 in Arabidopsis not only increased the chlorophyll content under cold stress, but also improved the cold tolerance. After silencing of BcWRKY53, there was a decrease in chlorophyll content and an increase in cold sensitivity. BcWRKY53 could inhibit self-expression by binding W-boxes in its own promoter. In addition, histone deacetylase 9 (BcHDA9) interacted with BcWRKY53 to inhibit BcWRKY53-mediated transcriptional activation. When ectopically overexpressed, BcHDA9 negatively regulates chlorophyll content and cold tolerance under cold treatment. Taken together, this study demonstrated that the cold-inducible transcription factor BcWRKY53 positively regulates BcCHLH and BcGUN4 under the regulation of self-regulation and BcHDA9 interactions. In this way, BcWRKY53 is actively involved in chlorophyll synthesis and the establishment of cold tolerance, which providing practical theoretical support in molecular characterization of cold tolerance and variety selection of non-heading Chinese cabbage.

Genome-wide identification of wheat USP gene family and functional dissection of TaUSP85 involved in heat tolerance

A collection of conserved proteins known as universal stress protein (USP) is present in a wide range of species, including plants, fungi, bacteria, and animals. USPs are named for their ability to respond to a variety of stress conditions, such as heat stroke, osmotic stress, nutrient limitation, and exposure to toxins or antibiotics. While the USP response to different stress conditions in plants has been reported, little is known about the USP family in wheat (Triticum aestivum L.). In wheat, we identified 88 USP genes distributed across 21 chromosomes classified into four subfamilies. Phylogenetic tree and synteny analysis across multiple species revealed a highly conserved evolution of the USP family between monocots and dicots. Based on comparative analysis of protein domains, gene structure and conserved motifs, TaUSPs showed significant differences among the four subfamilies. Furthermore, expression pattern analysis of TaUSPs showed significant differences among various tissues and under different abiotic stress conditions. We further conducted transformation experiments with the TaUSP85 gene, which significantly enhanced yeast thermotolerance. Silencing of TaUSP85 through VIGS experiments in wheat resulted in significant wilting, decreased chlorophyll content, and increased MDA accumulation compared to control plants. The silenced plant lines had much more ROS accumulation than the control group, as determined by the findings of DAB and NBT staining. The interaction proteins TaUSP1 and TaUSP11 of TaUSP85 were screened by yeast two-hybrid and their interaction relationship was further verified by LCI. Overall, our findings enhance the comprehension of the USP gene family in wheat and provide a valuable resource for further investigation of these genes in wheat and related cereal crops.

LlbHLH87 interacts with LlSPT to modulate thermotolerance via activation of LlHSFA2 and LlEIN3 in lily

Basic helix-loop-helix (bHLH) proteins comprise one of the largest families of transcription factors in plants, which play roles in plant development, secondary metabolism, and the response to biotic/abiotic stresses. However, the roles of bHLH proteins in thermotolerance are largely unknown. Herein, we identified a heat-inducible member of the bHLH family in lily (Lilium longiflorum), named LlbHLH87, which plays a role in thermotolerance. LlbHLH87 was rapidly induced by transient heat stress, and its encoded protein was localized to the nucleus, exhibiting transactivation activity in both yeast and plant cells. Overexpression of LlbHLH87 in Arabidopsis enhanced basal thermotolerance, while silencing of LlbHLH87 in lily reduced basal thermotolerance. Further analysis showed that LlbHLH87 bound to the promoters of HEAT STRESS TRANSCRIPTION FACTOR A2 (LlHSFA2) and ETHYLENE-INSENSITIVE 3 (LlEIN3) to directly activate their expression. In addition, LlbHLH87 interacted with itself and with SPATULA (LlSPT) protein. LlSPT was activated by extended heat stress and its protein competed for the homologous interaction of LlbHLH87, which reduced the transactivation ability of LlbHLH87 for target genes. Compared with that observed under LlbHLH87 overexpression alone, co-overexpression of LlbHLH87 and LlSPT reduced the basal thermotolerance of lily to sudden heat shock, but improved its thermosensitivity to prolonged heat stress treatment. Overall, our data demonstrated that LlbHLH87 regulates thermotolerance via activation of LlEIN3 and LlHSFA2, along with an antagonistic interaction with LlSPT.

PlWRKY47 Coordinates With Cytosolic Glyceraldehyde-3-Phosphate Dehydrogenase 2 Gene to Improve Thermotolerance Through Inhibiting Reactive Oxygen Species Generation in Herbaceous Peony

Although WRKY transcription factors play crucial roles in plant responses to high-temperature stress, little is known about Group IIb WRKY family members. Here, we identified the WRKY-IIb protein PlWRKY47 from herbaceous peony (Paeonia lactiflora Pall.), which functioned as a nuclear-localized transcriptional activator. The expression level of PlWRKY47 was positively correlated with high-temperature tolerance. Silencing of PlWRKY47 in P. lactiflora resulted in the decreased tolerance to high-temperature stress by accumulating reactive oxygen species (ROS). Overexpression of PlWRKY47 improved plant high-temperature tolerance through decreasing ROS accumulation. Moreover, PlWRKY47 directly bound to the promoter of cytosolic glyceraldehyde-3-phosphate dehydrogenase 2 (PlGAPC2) gene and activated its transcription. PlGAPC2 was also positively regulated high-temperature tolerance in P. lactiflora by increasing NAD+ content to inhibit ROS generation. Additionally, PlWRKY47 physically interacted with itself to form a homodimer, and PlWRKY47 could also interact with one Group IIb WRKY family member PlWRKY72 to form a heterodimer, they all promoted PlWRKY47 to bind to and activate PlGAPC2. These data support that the PlWRKY47-PlWRKY47 homodimer and PlWRKY72-PlWRKY47 heterodimer can directly activate PlGAPC2 expression to improve high-temperature tolerance by inhibiting ROS generation in P. lactiflora. These results will provide important insights into the plant high-temperature stress response by WRKY-IIb transcription factors.

The MdHSC70-MdWRKY75 module mediates basal apple thermotolerance by regulating the expression of heat shock factor genes

Heat stress severely restricts the growth and fruit development of apple (Malus domestica). Little is known about the involvement of WRKY proteins in the heat tolerance mechanism in apple. In this study, we found that the apple transcription factor (TF) MdWRKY75 responds to heat and positively regulates basal thermotolerance. Apple plants that overexpressed MdWRKY75 were more tolerant to heat stress while silencing MdWRKY75 caused the opposite phenotype. RNA-seq and reverse transcription quantitative PCR showed that heat shock factor genes (MdHsfs) could be the potential targets of MdWRKY75. Electrophoretic mobility shift, yeast one-hybrid, β-glucuronidase, and dual-luciferase assays showed that MdWRKY75 can bind to the promoters of MdHsf4, MdHsfB2a, and MdHsfA1d and activate their expression. Apple plants that overexpressed MdHsf4, MdHsfB2a, and MdHsfA1d exhibited heat tolerance and rescued the heat-sensitive phenotype of MdWRKY75-Ri3. In addition, apple heat shock cognate 70 (MdHSC70) interacts with MdWRKY75, as shown by yeast two-hybrid, split luciferase, bimolecular fluorescence complementation, and pull-down assays. MdHSC70 acts as a negative regulator of the heat stress response. Apple plants that overexpressed MdHSC70 were sensitive to heat, while virus-induced gene silencing of MdHSC70 enhanced heat tolerance. Additional research showed that MdHSC70 exhibits heat sensitivity by interacting with MdWRKY75 and inhibiting MdHsfs expression. In summary, we proposed a mechanism for the response of apple to heat that is mediated by the "MdHSC70/MdWRKY75-MdHsfs" molecular module, which enhances our understanding of apple thermotolerance regulated by WRKY TFs.

SlWRKY55 coordinately acts with SlVQ11 to enhance tomato thermotolerance by activating SlHsfA2

High temperature (HT) severely restricts plant growth, development, and productivity. Plants have evolved a set of mechanisms to cope with HT, including the regulation of heat stress transcription factors (Hsfs) and heat shock proteins (Hsps). However, it is not clear how the transcriptional and translational levels of Hsfs and Hsps are controlled in tomato. Here, we reported that the HT-induced transcription factor SlWRKY55 recruited SlVQ11 to coordinately regulate defense against HT. SlWRKY55 directly bound to the promoter of SlHsfA2 and promoted its expression, which was increased by SlVQ11. Moreover, both SlWRKY55 and SlVQ11 physically interacted with SlHsfA2 to enhance the transcriptional activity of SlHsfA2. Thus, our results revealed a molecular mechanism that the SlWRKY55/SlVQ11-SlHsfA2 cascade enhanced thermotolerance and provided potential target genes for improving the adaptability of crops to HT.

Heat-induced modulation of flavonoid biosynthesis via a LhMYBC2-Mediated regulatory network in oriental hybrid lily

Global warming significantly threatens crop production, and adversely affects plant physiology due to rising temperatures. Oriental hybrid lily, an ornamental plant of economic importance, experiences flower color changes in response to elevated temperatures. Anthocyanins belong to a subgroup of flavonoids and are the primary pigments responsible for the coloration of oriental hybrid lily petals. However, the regulatory mechanisms governing flavonoid biosynthesis under high temperature conditions in lilies remain poorly understood. In this study, we revealed the altered metabolite profiles in flavonoid biosynthesis using quasi-targeted metabolomic and transcriptomic analyses. Isoflavonoids accumulate substantially under high temperature conditions, whereas the accumulation of anthocyanin decreases. The expression of the isoflavone reductase gene (LhIFR) and the transcription factor LhMYBC2 were upregulated in response to high temperatures. The LhMYBC2 protein, which belongs to Subgroup 4-AtMYB4, competes with the anthocyanin positive regulator LhMYBA1 for the LhTT8 partner, thereby repressing the formation of a positively regulated transcription complex. Heterologous overexpression of LhMYBC2 in tobacco led to reduced anthocyanin accumulation and increased isoflavonoid accumulation, corroborating its role in inhibiting anthocyanin biosynthesis. This study proposes a regulatory model wherein LhMYBC2 acts as a mediator of flavonoid biosynthesis, influencing the coloration of lily flowers under high-temperature stress. These findings deepen our understanding of the metabolic and transcriptional responses of lily to heat stress and underscore the potential role of LhMYBC2 in mitigating anthocyanin accumulation.

LzSCL9, a Novel GRAS Transcription Factor in Lanzhou Lily (Lilium davidii var. unicolor), Participates in Regulation of Trichokonins-Primed Heat Stress Tolerance

In our previous research, we found that trichokonins' (TKs) employment improved the thermotolerance of the Lanzhou lily, a renowned edible crop species endemic to China that is relatively susceptible to high temperatures (HTs). Here, a novel Lanzhou lily GRAS gene, LzSCL9, was identified to respond to heat stress (HS) and HS+TKs treatment based on transcriptome and RT-qPCR analysis. TKs could improve the upregulation of LzSCL9 during long-term HS. The expression profile of LzSCL9 in response to HS with or without TKs treatment showed a significant positive correlation with LzHsfA2a-1, which was previously identified as a key regulator in TKs' conferred resilience to HT. More importantly, overexpression of LzSCL9 in the lily enhanced its tolerance to HTs and silencing LzSCL9 in the lily reduced heat resistance. Taken together, this study identified the positive role of LzSCL9 in TK-induced thermotolerance, thereby preliminarily establishing a molecular mechanism on TKs regulating the thermostability of the Lanzhou lily and providing a new candidate regulator for plant heat-resistant breeding.

Exploring Agrobacterium-mediated genetic transformation methods and its applications in Lilium

As a typical bulb flower, lily is widely cultivated worldwide because of its high ornamental, medicinal and edible value. Although breeding efforts evolved over the last 10000 years, there are still many problems in the face of increasing consumer demand. The approach of biotechnological methods would help to solve this problem and incorporate traits impossible by conventional breeding. Target traits are dormancy, development, color, floral fragrance and resistances against various biotic and abiotic stresses, so as to improve the quality of bulbs and cut flowers in planting, cultivation, postharvest, plant protection and marketing. Genetic transformation technology is an important method for varietal improvement and has become the foundation and core of plant functional genomics research, greatly assisting various plant improvement programs. However, achieving stable and efficient genetic transformation of lily has been difficult worldwide. Many gene function verification studies depend on the use of model plants, which greatly limits the pace of directed breeding and germplasm improvement in lily. Although significant progress has been made in the development and optimization of genetic transformation systems, shortcomings remain. Agrobacterium-mediated genetic transformation has been widely used in lily. However, severe genotypic dependence is the main bottleneck limiting the genetic transformation of lily. This review will summarizes the research progress in the genetic transformation of lily over the past 30 years to generate the material including a section how genome engineering using stable genetic transformation system, and give an overview about recent and future applications of lily transformation. The information provided in this paper includes ideas for optimizing and improving the efficiency of existing genetic transformation methods and for innovation, provides technical support for mining and identifying regulatory genes for key traits, and lays a foundation for genetic improvement and innovative germplasm development in lily.

Research Progress on Heat Stress Response Mechanism and Control Measures in Medicinal Plants

Medicinal plants play a pivotal role in traditional medicine and modern pharmacology due to their various bioactive compounds. However, heat stress caused by climate change will seriously affect the survival and quality of medicinal plants. In this review, we update our understanding of the research progress on medicinal plants' response mechanisms and control measures under heat stress over the last decade. This includes physiological changes, molecular mechanisms, and technical means to improve the heat tolerance of medicinal plants under heat stress. It provides a reference for cultivating heat-resistant varieties of medicinal plants and the rational utilization of control measures to improve the heat resistance of medicinal plants.

MicroRNAs Involved in Nutritional Regulation During Plant-Microbe Symbiotic and Pathogenic Interactions with Rice as a Model

Plants are constantly challenged with numerous adverse environmental conditions, including biotic and abiotic stresses. Coordinated regulation of plant responses requires crosstalk between regulatory pathways initiated by different external cues. Stress induced by excessiveness or deficiency of nutrients has been shown to positively or negatively interact with pathogen-induced immune responses. Also, colonization by arbuscular mycorrhizal (AM) fungi can improve plant nutrition, mainly phosphorus and resistance to pathogen infection. The proposed review addresses these issues about a new question that integrates adaptation to nutrient stress and disease resistance. The main goal of the current review is to provide insights into the interconnected regulation between nutrient signaling and immune signaling pathways in rice, focusing on phosphate, potassium and iron signaling. The underpinnings of plant/pathogen/AM fungus interaction concerning rice/M. oryzae/R. irregularis is highlighted. The role of microRNAs (miRNAs) involved in Pi (miR399, miR827) and Fe (miR7695) homeostasis in pathogenic/symbiotic interactions in rice is discussed. The intracellular dynamics of membrane proteins that function in nutrient transport transgenic rice lines expressing fluorescent protein fusion genes are outlined. Integrating functional genomic, nutritional and metal content, molecular and cell biology approaches to understand how disease resistance is regulated by nutrient status leading to novel concepts in fundamental processes underlying plant disease resistance will help to devise novel strategies for crop protection with less input of pesticides and fertilizers.

Functional validation of AaCaM3 response to high temperature stress in Amorphophallus albus

Amorphophallus is a perennial monocotyledonous herbaceous plant native to the southwestern region of China, widely used in various fields such as food processing, biomedicine and chemical agriculture. However, Amorphophallus is a typical thermolabile plant, and the continuous high temperature in summer have seriously affected the growth, development and economic yield of Amorphophallus in recent years. Calmodulin (CaM), a Ca2+ sensor ubiquitous in eukaryotes, is the most important multifunctional receptor protein in plant cells, which affects plant stress resistance by participating in the activities of a variety of signaling molecules. In this study, the key gene AaCaM3 for the Ca2+-CaM regulatory pathway was obtained from A. albus, the sequence analysis confirmed that it is a typical calmodulin. The qRT-PCR results demonstrated that with the passage of heat treatment time, the expression of AaCaM3 was significantly upregulated in A. albus leaves. Subcellular localization analysis revealed that AaCaM3 localized on the cytoplasm and nucleus. Meanwhile, heterologous transformation experiments have shown that AaCaM3 can significantly improve the heat tolerance of Arabidopsis under heat stress. The promoter region of AaCaM3 was sequenced 1,338 bp by FPNI-PCR and GUS staining assay showed that the promoter of AaCaM3 was a high-temperature inducible promoter. Yeast one-hybrid analysis and Luciferase activity reporting system analysis showed that the AaCaM3 promoter may interact with AaHSFA1, AaHSFA2c, AaHSP70, AaDREB2a and AaDREB2b. In conclusion, this study provides new ideas for further improving the signal transduction network of high-temperature stress in Amorphophallus.

WRKY Transcription Factor Responses and Tolerance to Abiotic Stresses in Plants

Plants are subjected to abiotic stresses throughout their developmental period. Abiotic stresses include drought, salt, heat, cold, heavy metals, nutritional elements, and oxidative stresses. Improving plant responses to various environmental stresses is critical for plant survival and perpetuation. WRKY transcription factors have special structures (WRKY structural domains), which enable the WRKY transcription factors to have different transcriptional regulatory functions. WRKY transcription factors can not only regulate abiotic stress responses and plant growth and development by regulating phytohormone signalling pathways but also promote or suppress the expression of downstream genes by binding to the W-box [TGACCA/TGACCT] in the promoters of their target genes. In addition, WRKY transcription factors not only interact with other families of transcription factors to regulate plant defence responses to abiotic stresses but also self-regulate by recognising and binding to W-boxes in their own target genes to regulate their defence responses to abiotic stresses. However, in recent years, research reviews on the regulatory roles of WRKY transcription factors in higher plants have been scarce and shallow. In this review, we focus on the structure and classification of WRKY transcription factors, as well as the identification of their downstream target genes and molecular mechanisms involved in the response to abiotic stresses, which can improve the tolerance ability of plants under abiotic stress, and we also look forward to their future research directions, with a view of providing theoretical support for the genetic improvement of crop abiotic stress tolerance.

Genome-wide identification of WRKY transcription factors in Casuarina equisetifolia and the function analysis of CeqWRKY11 in response to NaCl/NaHCO3 stresses

BACKGROUND

Casuarina equisetifolia (C. equisetifolia) is a woody species with many excellent features. It has natural resistance against drought, salt and saline-alkali stresses. WRKY transcription factors (TFs) play significant roles in plant response to abiotic stresses, therefore, molecular characterization of WRKY gene family under abiotic stresses holds great significance for improvement of forest trees through molecular biological tools. At present, WRKY TFs from C. equisetifolia have not been thoroughly studied with respect to their role in salt and saline-alkali stresses response. The current study was conducted to bridge the same knowledge gap.

RESULTS

A total of 64 WRKYs were identified in C. equisetifolia and divided into three major groups i.e. group I, II and III, consisting of 10, 42 and 12 WRKY members, respectively. The WRKY members in group II were further divided into 5 subgroups according to their homology with Arabidopsis counterparts. WRKYs belonging to the same group exhibited higher similarities in gene structure and the presence of conserved motifs. Promoter analysis data showed the presence of various response elements, especially those related to hormone signaling and abiotic stresses, such as ABRE (ABA), TGACG (MeJA), W-box ((C/T) TGAC (T/C)) and TC-rich motif. Tissue specific expression data showed that CeqWRKYs were mainly expressed in root under normal growth conditions. Furthermore, most of the CeqWRKYs were up-regulated by NaCl and NaHCO3 stresses with few of WRKYs showing early responsiveness to both stresses while few others exhibiting late response. Although the expressions of CeqWRKYs were also induced by cold stress, the response was delayed compared with other stresses. Transgenic C. equisetifolia plants overexpressing CeqWRKY11 displayed lower electrolyte leakage, higher chlorophyll content, and enhanced tolerance to both stresses. The higher expression of abiotic stress related genes, especially CeqHKT1 and CeqPOD7, in overexpression lines points to the maintenance of optimum Na+/K+ ratio, and ROS scavenging as possible key molecular mechanisms underlying salt stress tolerance.

CONCLUSIONS

Our results show that CeqWRKYs might be key regulators of NaCl and NaHCO3 stresses response in C. equisetifolia. In addition, positive correlation of CeqWRKY11 expression with increased stress tolerance in C. equisetifolia encourages further research on other WRKY family members through functional genomic tools. The best candidates could be incorporated in other woody plant species for improving stress tolerance.

WRKY22 Transcription Factor from Iris laevigata Regulates Flowering Time and Resistance to Salt and Drought

Iris laevigata Fisch. is an excellent ornamental plant in cold regions due to its unique ornamental ability and strong cold resistance. However, the flowering period of the population is only about 20 days, greatly limiting its potential uses in landscaping and the cutting flower industry. In addition, I. laevigata is often challenged with various abiotic stresses including high salinity and drought in its native habitats. Thus, breeding novel cultivars with delayed flowering time and higher resistance to abiotic stress is of high importance. In this study, we utilized sequencing data from the I. laevigata transcriptome to identify WRKYs and characterized IlWRKY22, a key transcription factor that modulates flowering time and abiotic stress responses. IlWRKY22 is induced by salt and drought stress. We cloned IlWRKY22 and found that it is a Group IIe WRKY localized in the nucleus. Overexpressing IlWRKY22 in Arabidopsis thaliana (L.) Heynh. and Nicotiana tabacum L. resulted in a delayed flowering time in the transgenic plants. We created transgenic N. tabacum overexpressing IlWRKY22, which showed significantly improved resistance to both salt and drought compared to the control plants. Thus, our study revealed a unique dual function of IlWRKY22, an excellent candidate gene for breeding novel Iris cultivars of desirable traits.

Regulation of the trade-off between cold stress and growth by glutathione S-transferase phi class 10 (BcGSTF10) in non-heading Chinese cabbage

Cold stress is a serious threat to global crop production and food security, but plant cold resistance is accompanied by reductions in growth and yield. In this study, we determined that the novel gene BcGSTF10 in non-heading Chinese cabbage [NHCC; Brassica campestris (syn. Brassica rapa) ssp. chinensis] is implicated in resistance to cold stress. Biochemical and genetic analyses demonstrated that BcGSTF10 interacts with BcICE1 to induce C-REPEAT BINDING FACTOR (CBF) genes that enhance freezing tolerance in NHCC and in Arabidopsis. However, BcCBF2 represses BcGSTF10 and the latter promotes growth in NHCC and Arabidopsis. This dual function of BcGSTF10 indicates its pivotal role in balancing cold stress and growth, and this important understanding has the potential to inform the future development of strategies to breed crops that are both climate-resilient and high-yielding.

Lily LlHSFC2 coordinates with HSFAs to balance heat stress response and improve thermotolerance

Heat stress transcription factors (HSFs) are core regulators of plant heat stress response. Much research has focused on class A and B HSFs, leaving those of class C relatively understudied. Here, we reported a lily (Lilium longiflorum) heat-inducible HSFC2 homology involved in thermotolerance. LlHSFC2 was located in the nucleus and cytoplasm and exhibited a repression ability by binding heat stress element. Overexpression of LlHSFC2 in Arabidopsis, tobacco (Nicotiana benthamiana), and lily, all increased the thermotolerance. Conversely, silencing of LlHSFC2 in lily reduced its thermotolerance. LlHSFC2 could interact with itself, or interact with LlHSFA1, LlHSFA2, LlHSFA3A, and LlHSFA3B of lily, AtHSFA1e and AtHSFA2 of Arabidopsis, and NbHSFA2 of tobacco. LlHSFC2 interacted with HSFAs to accelerate their transactivation ability and act as a transcriptional coactivator. Notably, compared with the separate LlHSFA3A overexpression, co-overexpression of LlHSFC2/LlHSFA3A further enhanced thermotolerance of transgenic plants. In addition, after suffering HS, the homologous interaction of LlHSFC2 was repressed, but its heterologous interaction with the heat-inducible HSFAs was promoted, enabling it to exert its co-activation effect for thermotolerance establishment and maintenance. Taken together, we identified that LlHSFC2 plays an active role in the general balance and maintenance of heat stress response by cooperating with HSFAs, and provided an important candidate for the enhanced thermotolerance breeding of crops and horticulture plants.

Physiological and transcriptional analyses reveal the resistance mechanisms of kiwifruit (Actinidia chinensis) mutant with enhanced heat tolerance

High temperature is an environmental stressor that severely threatens plant growth, development, and yield. In this study, we obtained a kiwifruit mutant (MT) of 'Hongyang' (WT) through 60Co-γ irradiation. The MT possessed different leaf morphology and displayed prominently elevated heat tolerance compared to the WT genotype. When exposure to heat stress, the MT plants exhibited stabler photosynthetic capacity and accumulated less reactive oxygen species, along with enhanced antioxidant capacity and higher expression levels of related genes in comparison with the WT plants. Moreover, global transcriptome profiling indicated that an induction in genes related to stress-responsive, phytohormone signaling, and transcriptional regulatory pathways, which might contribute to the upgrade of thermotolerance in the MT genotype. Collectively, the significantly enhanced thermotolerance of MT might be mainly attributed to profitable leaf structure variations, improved photosynthetic and antioxidant capacities, as well as extensive transcriptome reprogram. These findings would be insightful in elucidating the sophisticated mechanisms of kiwifruit response to heat stress, and suggest the MT holds great potential for future kiwifruit improvement with enhanced heat tolerance.

WRKY Transcriptional Factor IlWRKY70 from Iris laevigata Enhances Drought and Salinity Tolerances in Nicotiana tabacum

Drought and high salinity greatly affect plant growth and development. WRKY transcription factors play a key role in plant tolerance to abiotic stress, but the functions of WRKYs in the ornamental monocotyledon Iris laevigata remain largely unexplored. In this study, we cloned IlWRKY70 and found that it is a Group III WRKY localized in the nucleus. The expression of IlWRKY70 was induced by NaCl and PEG-6000, which reached peaks (4.38 and 5.65 times) after 3 h and 1 h, respectively. The exogenous overexpression of IlWRKY70 in N. tabacum significantly improved the resistance under NaCl and drought treatments, as evidenced by higher germination rates, longer root lengths, and increased fresh weights compared to those of control plants. In addition, transgenic seedlings showed significantly reduced wilting, higher photosynthetic performance, higher Fv/Fm and chlorophyll content, and lower stomatal conductance. Moreover, transgenic lines showed higher antioxidant enzymatic activities, lower reactive oxygen species (ROS), and lower malondialdehyde contents. Accordingly, we also found higher expressions of antioxidant defense genes, including SOD, CAT, and POD, in transgenic lines compared to controls under salt and drought stresses. Thus, IlWRKY70 enhances the abilities of salt and drought tolerances in plants, at least partially, via ROS regulation and can be used for breeding I. laevigata possessing enhanced salt and drought resistances.

Low LdMYB12 expression contributes to petal spot deficiency in Lilium davidii var. unicolor

Petal spots are widespread in plants, they are important for attracting pollinators and as economic traits in crop breeding. However, the genetic and developmental control of petal spots has seldom been investigated. To further clarify the development of petal spots formation, we performed comparative transcriptome analysis of Lilium davidii var. unicolor and Lilium davidii petals at the full-bloom stage. In comparison with the parental species L. davidii, petals of the lily variety L. davidii var. unicolor do not have the distinct anthocyanin spots. We show that among 7846 differentially expressed genes detected, LdMYB12 was identified as a candidate gene contributing to spot formation in lily petals. The expression level of LdMYB12 in the petals of L. davidii was higher than that in L. davidii var. unicolor petals. Moreover, overexpression of LdMYB12 led to the appearance of spots on the petals of L. davidii var. unicolor, accompanied by increased expression of anthocyanin synthesis-related genes. Taken together, these results indicate that abnormal expression of LdMYB12 contributes to petal spot deficiency in L. davidii var. unicolor.

Epigenetic silencing of callose synthase by VIL1 promotes bud-growth transition in lily bulbs

In plants, restoring intercellular communication is required for cell activity in buds during the growth transition from slow to fast growth after dormancy release. However, the epigenetic regulation of this phenomenon is far from understood. Here we demonstrate that lily VERNALIZATION INSENSITIVE 3-LIKE 1 (LoVIL1) confers growth transition by mediating plasmodesmata opening via epigenetic repression of CALLOSE SYNTHASE 3 (LoCALS3). Moreover, we found that a novel transcription factor, NUCLEAR FACTOR Y, SUBUNIT A7 (LoNFYA7), is capable of recruiting the LoVIL1-Polycomb Repressive Complex 2 (PRC2) and enhancing H3K27me3 at the LoCALS3 locus by recognizing the CCAAT cis-element (Cce) of its promoter. The LoNFYA7-LoVIL1 module serves as a key player in orchestrating the phase transition from slow to fast growth in lily bulbs. These studies also indicate that LoVIL1 is a suitable marker for the bud-growth-transition trait following dormancy release in lily cultivars.

BcWRKY22 Activates BcCAT2 to Enhance Catalase (CAT) Activity and Reduce Hydrogen Peroxide (H2O2) Accumulation, Promoting Thermotolerance in Non-Heading Chinese Cabbage (Brassica campestris ssp. chinensis)

WRKY transcription factors (TFs) participate in plant defense mechanisms against biological and abiotic stresses. However, their regulatory role in heat resistance is still unclear in non-heading Chinese cabbage. Here, we identified the WRKY-IIe gene BcWRKY22(BraC09g001080.1), which is activated under high temperatures and plays an active role in regulating thermal stability, through transcriptome analysis. We further discovered that the BcWRKY22 protein is located in the nucleus and demonstrates transactivation activity in both the yeast and plant. Additionally, our studies showed that the transient overexpression of BcWRKY22 in non-heading Chinese cabbage activates the expression of catalase 2 (BcCAT2), enhances CAT enzyme activity, and reduces Hydrogen Peroxide (H2O2) accumulation under heat stress conditions. In addition, compared to its wild-type (WT) counterparts, Arabidopsis thaliana heterologously overexpresses BcWRKY22, improving thermotolerance. When the BcWRKY22 transgenic root was obtained, under heat stress, the accumulation of H2O2 was reduced, while the expression of catalase 2 (BcCAT2) was upregulated, thereby enhancing CAT enzyme activity. Further analysis revealed that BcWRKY22 directly activates the expression of BcCAT2 (BraC08g016240.1) by binding to the W-box element distributed within the promoter region of BcCAT2. Collectively, our findings suggest that BcWRKY22 may serve as a novel regulator of the heat stress response in non-heading Chinese cabbage, actively contributing to the establishment of thermal tolerance by upregulating catalase (CAT) activity and downregulating H2O2 accumulation via BcCAT2 expression.

Multifaceted roles of LhWRKY44 in promoting anthocyanin accumulation in Asiatic hybrid lilies (Lilium spp.)

The Asiatic hybrid lily (Lilium spp.) is a horticultural crop with high commercial value and diverse anthocyanin pigmentation patterns. However, the regulatory mechanism underlying lily flower color has been largely unexplored. Here, we identified a WRKY transcription factor from lily tepals, LhWRKY44, whose expression was closely associated with anthocyanin accumulation. Functional verification indicated that LhWRKY44 positively regulated anthocyanin accumulation. LhWRKY44 physically interacted with LhMYBSPLATTER and directly bound to the LhMYBSPLATTER promoter, which enhanced the effect of the LhMYBSPLATTER-LhbHLH2 MBW complex activator on anthocyanin accumulation. Moreover, EMSA and dual-luciferase assays revealed that LhWRKY44 activated and bound to the promoters of gene LhF3H and the intracellular anthocyanin-related glutathione S-transferase gene LhGST. Interestingly, our further results showed that LhWRKY44 participated in light and drought-induced anthocyanin accumulation, and improved the drought tolerance in lily via activating stress-related genes. These results generated a multifaceted regulatory mechanism for the LhWRKY44-meditaed enhancement by the environmental signal pathway of anthocyanin accumulation and expanded our understanding of the WRKY-mediated transcriptional regulatory hierarchy modulating anthocyanin accumulation in Asiatic hybrid lilies.

A LlMYB305-LlC3H18-LlWRKY33 module regulates thermotolerance in lily

The CCCH proteins play important roles in plant growth and development, hormone response, pathogen defense and abiotic stress tolerance. However, the knowledge of their roles in thermotolerance are scarce. Here, we identified a heat-inducible CCCH gene LlC3H18 from lily. LlC3H18 was localized in the cytoplasm and nucleus under normal conditions, while it translocated in the cytoplasmic foci and co-located with the markers of two messenger ribonucleoprotein (mRNP) granules, processing bodies (PBs) and stress granules (SGs) under heat stress conditions, and it also exhibited RNA-binding ability. In addition, LlC3H18 exhibited transactivation activity in both yeast and plant cells. In lily and Arabidopsis, overexpression of LlC3H18 damaged their thermotolerances, and silencing of LlC3H18 in lily also impaired its thermotolerance. Similarly, Arabidopsis atc3h18 mutant also showed decreased thermotolerance. These results indicated that the appropriate expression of C3H18 was crucial for establishing thermotolerance. Further analysis found that LlC3H18 directly bound to the promoter of LlWRKY33 and activated its expression. Besides, it was found that LlMYB305 acted as an upstream factor of LlC3H18 and activated its expression. In conclusion, we demonstrated that there may be a LlMYB305-LlC3H18-LlWRKY33 regulatory module in lily that is involved in the establishment of thermotolerance and finely regulates heat stress response.

Enhancing heat stress tolerance in Lanzhou lily (Lilium davidii var. unicolor) with Trichokonins isolated from Trichoderma longibrachiatum SMF2

Lanzhou lily (Lilium davidii var. unicolor) is a renowned edible crop produced in China and relatively sensitive to high temperature (HT). Trichokonins (TKs) are antimicrobial peptaibols secreted from Trichoderma longibrachiatum strain SMF2. Here, we report that TKs application improves the thermotolerance of Lanzhou lily. The activity of the antioxidant enzyme system (SOD, CAT, and POD), the level of heat-resistance-associated phytohormones (ABA, SA, and JA), the relative water content (RWC), the content of chlorophyll (Chl), and the net photosynthetic rate (P _n) were promoted by TKs treatment in Lanzhou lily plants subjected to heat stress (HS). TKs treatment also mitigated cell injury as shown by a lower accumulation of malondialdehyde (MDA) and relative electrolyte leakage (REL) under HS conditions. RNA-seq data analysis showed that more than 4.5 times differentially expressed genes (DEGs) responded to TKs treatment under HS compared to non-HS, and TKs treatment reduced protein folding and enhanced cellular repair function under HS conditions. The analyses of DEGs involved in hormone (ABA, SA and JA) synthesis and signaling pathways suggested that TKs might improve Lanzhou lily heat tolerance by promoting ABA synthesis and signal transduction. TKs highly induced DEGs of the HSF-HSP pathway under HS, in which HSFA2 accounted for most of the HSF family. Furthermore, TKs treatment resulted in the upregulation of heat-protective genes LzDREB2B, LzHsfA2a, LzMBF1c, LzHsp90, and LzHsp70 involved in HSF-HSP signal pathway after long-term HS. LzHsfA2a-1 likely plays a key role in acquisition of TKs-induced thermotolerance of Lanzhou lily as evidenced by the sustained response to HS, the enhanced response to TKs treatment under long-term HS, and the high sequence similarity to LlHsfA2a which is a key regulator for the improvement of heat tolerance in Lilium longiflorum. Our results reveal the underlying mechanisms of TKs-mediated thermotolerance in Lanzhou lily and highlight an attractive approach to protecting crop plants from damage caused by HS in a global warming future.

Advances in the Research on Plant WRKY Transcription Factors Responsive to External Stresses

The WRKY transcription factors are a class of transcriptional regulators that are ubiquitous in plants, wherein they play key roles in various physiological activities, including responses to stress. Specifically, WRKY transcription factors mediate plant responses to biotic and abiotic stresses through the binding of their conserved domain to the W-box element of the target gene promoter and the subsequent activation or inhibition of transcription (self-regulation or cross-regulation). In this review, the progress in the research on the regulatory effects of WRKY transcription factors on plant responses to external stresses is summarized, with a particular focus on the structural characteristics, classifications, biological functions, effects on plant secondary metabolism, regulatory networks, and other aspects of WRKY transcription factors. Future research and prospects in this field are also proposed.