ABF3 enhances drought tolerance via promoting ABA-induced stomatal closure by directly regulating ADF5 in Populus euphratica

BnaABF3 and BnaMYB44 regulate the transcription of zeaxanthin epoxidase genes in carotenoid and abscisic acid biosynthesis

Zeaxanthin epoxidase (ZEP) is a key enzyme that catalyzes the conversion of zeaxanthin to violaxanthin in the carotenoid and abscisic acid (ABA) biosynthesis pathways. The rapeseed (Brassica napus) genome has 4 ZEP (BnaZEP) copies that are suspected to have undergone subfunctionalization, yet the 4 genes' underlying regulatory mechanisms remain unknown. Here, we genetically confirmed the functional divergence of the gene pairs BnaA09.ZEP/BnaC09.ZEP and BnaA07.ZEP/BnaC07.ZEP, which encode enzymes with tissue-specific roles in carotenoid and ABA biosynthesis in flowers and leaves, respectively. Molecular and transgenic experiments demonstrated that each BnaZEP pair is transcriptionally regulated via ABA-responsive element-binding factor 3 s (BnaABF3s) and BnaMYB44s as common and specific regulators, respectively. BnaABF3s directly bound to the promoters of all 4 BnaZEPs and activated their transcription, with overexpression of individual BnaABF3s inducing BnaZEP expression and ABA accumulation under drought stress. Conversely, loss of BnaABF3s function resulted in lower expression of several genes functioning in carotenoid and ABA metabolism and compromised drought tolerance. BnaMYB44s specifically targeted and repressed the expression of BnaA09.ZEP/BnaC09.ZEP but not BnaA07.ZEP/BnaC07.ZEP. Overexpression of BnaA07.MYB44 resulted in increased carotenoid content and an altered carotenoid profile in petals. Additionally, RNA-seq analysis indicated that BnaMYB44s functions as a repressor in phenylpropanoid and flavonoid biosynthesis. These findings provide clear evidence for the subfunctionalization of duplicated genes and contribute to our understanding of the complex regulatory network involved in carotenoid and ABA biosynthesis in B. napus.

Agricultural drought assessment in dry zones of Tolima, Colombia, using an approach based on water balance and vegetation water stress

Soil water balance is an essential element to consider for the management of droughts and agricultural land use. It is important to evaluate the water consumption of a crop in each of its phenological phases and the status of water reserves during critical hydrologic periods. This study developed an agricultural drought index (Standardized Soil Moisture Deficit Index - SMODI) conceptualized with a water balance model considering the vegetation stress caused by soil moisture deficit. This contribution was based on meteorological information, soil moisture from satellite images, hydrophysical properties of the soil and crop evapotranspiration. Information from 61 weather stations located in the dry zone of Tolima was used for estimating the water balance. SMODI was compared with the most common drought indexes: Standardized Precipitation - Evapotranspiration Index (SPEI), the Palmer Self-Calibrated Drought Index (scPDSI), and other eleven macroclimatic indexes. Pearson's correlation coefficients (r), Tukey's test, and analysis of variance were applied to analyze the degree of association between SMODI and the contrasting indexes on a quarterly basis. SMODI considers factors influencing soil moisture distribution and retention and the water stress thresholds that plants have evolved to withstand during drought periods. Consequently, this integrated approach enhances the assessment of agricultural drought by relying on pertinent physical processes. SMODI identified extremely dry, severe, moderate and normal drought 5 %, 3 %, 20 % and 72 % respectively conditions in areas characterized by Entisols, Inceptisols, and Andisols, where rice and fruit crops and pasturelands are cultivated. The SMODI has a good correlation with macroclimatic indexes (0.70 < r < 0.74).

Maize actin depolymerizing factor 1 (ZmADF1) negatively regulates pollen development

The normal development of pollen grains and the completion of double fertilization in embryos are crucial for both the sexual reproduction of angiosperms and grain production. Actin depolymerizing factor (ADF) regulates growth, development, and responses to biotic and abiotic stress by binding to actin in plants. In this study, the function of the ZmADF1 gene was validated through bioinformatic analysis, subcellular localization, overexpression in maize and Arabidopsis, and knockout via CRISPR/Cas9. The amino acid sequence of ZmADF1 exhibited high conservation and a similar tertiary structure to that of ADF homologs. Subcellular localization analysis revealed that ZmADF1 is localized mainly to the nucleus and cytoplasm. The ZmADF1 gene was specifically expressed in maize pollen, and overexpression of the ZmADF1 gene decreased the number of pollen grains in the anthers of transgenic Arabidopsis plants. The germination rate of pollen and the empty seed shell rate in the fruit pods of the overexpressing plants were significantly greater than those in the wild-type (WT) plants. In maize, the pollen viability of the knockout lines was significantly greater than that of both the WT and the overexpressing lines. Our results confirmed that the ZmADF1 gene was specifically expressed in pollen and negatively regulated pollen quantity, vigor, germination rate, and seed setting rate. This study provides insights into ADF gene function and possible pathways for improving high-yield maize breeding.

Stomatal density suppressor PagSDD1 is a "generalist" gene that promotes plant growth and improves water use efficiency

The serine protease SDD1 regulates stomatal density, but its potential impact on plant vegetative growth is unclear. Our study reveals a substantial upregulation of SDD1 in triploid poplar apical buds and leaves, suggesting its possible role in their growth regulation. We cloned PagSDD1 from poplar 84 K (Populus alba × P. glandulosa) and found that overexpression in poplar, soybean, and lettuce led to decreased leaf stomatal density. Furthermore, PagSDD1 represses PagEPF1, PagEPF2, PagEPFL9, PagSPCH, PagMUTE, and PagFAMA expression. In contrast, PagSDD1 promotes the expression of its receptors, PagTMM and PagERECTA. PagSDD1-OE poplars showed stronger drought tolerance than wild-type poplars. Simultaneously, PagSDD1-OE poplar, soybean, and lettuce had vegetative growth advantages. RNA sequencing revealed a significant upregulation of genes PagLHCB2.1 and PagGRF5, correlating positively with photosynthetic rate, and PagCYCA3;4 and PagEXPA8 linked to cell division and differentiation in PagSDD1-OE poplars. This increase promoted leaf photosynthesis, boosted auxin and cytokinin accumulation, and enhanced vegetative growth. SDD1 overexpression can increase the biomass of poplar, soybean, and lettuce by approximately 70, 176, and 155 %, respectively, and increase the water use efficiency of poplar leaves by over 52 %, which is of great value for the molecular design and breeding of plants with growth and water-saving target traits.

The WRKY46-MYC2 module plays a critical role in E-2-hexenal-induced anti-herbivore responses by promoting flavonoid accumulation

Volatile organic compounds (VOCs) play key roles in plant-plant communication, especially in response to pest attack. E-2-hexenal is an important component of VOCs, but it is unclear whether it can induce endogenous plant resistance to insects. Here, we show that E-2-hexenal activates early signaling events in Arabidopsis (Arabidopsis thaliana) mesophyll cells, including an H2O2 burst at the plasma membrane, the directed flow of calcium ions, and an increase in cytosolic calcium concentration. Treatment of wild-type Arabidopsis plants with E-2-hexenal increases their resistance when challenged with the diamondback moth Plutella xylostella L., and this phenomenon is largely lost in the wrky46 mutant. Mechanistically, E-2-hexenal induces the expression of WRKY46 and MYC2, and the physical interaction of their encoded proteins was verified by yeast two-hybrid, firefly luciferase complementation imaging, and in vitro pull-down assays. The WRKY46-MYC2 complex directly binds to the promoter of RBOHD to promote its expression, as demonstrated by luciferase reporter, yeast one-hybrid, chromatin immunoprecipitation, and electrophoretic mobility shift assays. This module also positively regulates the expression of E-2-hexenal-induced naringenin biosynthesis genes (TT4 and CHIL) and the accumulation of total flavonoids, thereby modulating plant tolerance to insects. Together, our results highlight an important role for the WRKY46-MYC2 module in the E-2-hexenal-induced defense response of Arabidopsis, providing new insights into the mechanisms by which VOCs trigger plant defense responses.

RtNAC055 promotes drought tolerance via a stomatal closure pathway linked to methyl jasmonate/hydrogen peroxide signaling in Reaumuria trigyna

The stomata regulate CO2 uptake and efficient water usage, thereby promoting drought stress tolerance. NAC proteins (NAM, ATAF1/2, and CUC2) participate in plant reactions following drought stress, but the molecular mechanisms underlying NAC-mediated regulation of stomatal movement are unclear. In this study, a novel NAC gene from Reaumuria trigyna, RtNAC055, was found to enhance drought tolerance via a stomatal closure pathway. It was regulated by RtMYC2 and integrated with jasmonic acid signaling and was predominantly expressed in stomata and root. The suppression of RtNAC055 could improve jasmonic acid and H2O2 production and increase the drought tolerance of transgenic R. trigyna callus. Ectopic expression of RtNAC055 in the Arabidopsis atnac055 mutant rescued its drought-sensitive phenotype by decreasing stomatal aperture. Under drought stress, overexpression of RtNAC055 in poplar promoted ROS (H2O2) accumulation in stomata, which accelerated stomatal closure and maintained a high photosynthetic rate. Drought upregulated the expression of PtRbohD/F, PtP5CS2, and PtDREB1.1, as well as antioxidant enzyme activities in heterologous expression poplars. RtNAC055 promoted H2O2 production in guard cells by directly binding to the promoter of RtRbohE, thus regulating stomatal closure. The stress-related genes RtDREB1.1/P5CS1 were directly regulated by RtNAC055. These results indicate that RtNAC055 regulates stomatal closure by maintaining the balance between the antioxidant system and H2O2 level, reducing the transpiration rate and water loss, and improving photosynthetic efficiency and drought resistance.

Research progress on the roles of actin-depolymerizing factor in plant stress responses

Actin-depolymerizing factors (ADFs) are highly conserved small-molecule actin-binding proteins found throughout eukaryotic cells. In land plants, ADFs form a small gene family that displays functional redundancy despite variations among its individual members. ADF can bind to actin monomers or polymerized microfilaments and regulate dynamic changes in the cytoskeletal framework through specialized biochemical activities, such as severing, depolymerizing, and bundling. The involvement of ADFs in modulating the microfilaments' dynamic changes has significant implications for various physiological processes, including plant growth, development, and stress response. The current body of research has greatly advanced our comprehension of the involvement of ADFs in the regulation of plant responses to both biotic and abiotic stresses, particularly with respect to the molecular regulatory mechanisms that govern ADF activity during the transmission of stress signals. Stress has the capacity to directly modify the transcription levels of ADF genes, as well as indirectly regulate their expression through transcription factors such as MYB, C-repeat binding factors, ABF, and 14-3-3 proteins. Furthermore, apart from their role in regulating actin dynamics, ADFs possess the ability to modulate the stress response by influencing downstream genes associated with pathogen resistance and abiotic stress response. This paper provides a comprehensive overview of the current advancements in plant ADF gene research and suggests that the identification of plant ADF family genes across a broader spectrum, thorough analysis of ADF gene regulation in stress resistance of plants, and manipulation of ADF genes through genome-editing techniques to enhance plant stress resistance are crucial avenues for future investigation in this field.

Aspartyl tRNA-synthetase (AspRS) gene family enhances drought tolerance in poplar through BABA-PtrIBIs-PtrVOZ signaling module

BACKGROUND

Drought stress is a prevalent abiotic stress that significantly hinders the growth and development of plants. According to studies, β-aminobutyric acid (BABA) can influence the ABA pathway through the AtIBI1 receptor gene to enhance cold resistance in Arabidopsis. However, the Aspartate tRNA-synthetase (AspRS) gene family, which acts as the receptor for BABA, has not yet been investigated in poplar. Particularly, it is uncertain how the AspRS gene family (PtrIBIs)r can resist drought stress after administering various concentrations of BABA to poplar.

RESULTS

In this study, we have identified 12 AspRS family genes and noted that poplar acquired four PtrIBI pairs through whole genome duplication (WGD). We conducted cis-action element analysis and found a significant number of stress-related action elements on different PtrIBI genes promoters. The expression of most PtrIBI genes was up-regulated under beetle and mechanical damage stresses, indicating their potential role in responding to leaf damage stress. Our results suggest that a 50 mM BABA treatment can alleviate the damage caused by drought stress in plants. Additionally, via transcriptome sequencing, we observed that the partial up-regulation of BABA receptor genes, PtrIBI2/4/6/8/11, in poplars after drought treatment. We hypothesize that poplar responds to drought stress through the BABA-PtrIBIs-PtrVOZ coordinated ABA signaling pathway. Our research provides molecular evidence for understanding how plants respond to drought stress through external application of BABA.

CONCLUSIONS

In summary, our study conducted genome-wide analysis of the AspRS family of P. trichocarpa and identified 12 PtrIBI genes. We utilized genomics and bioinformatics to determine various characteristics of PtrIBIs such as chromosomal localization, evolutionary tree, gene structure, gene doubling, promoter cis-elements, and expression profiles. Our study found that certain PtrIBI genes are regulated by drought, beetle, and mechanical damage implying their crucial role in enhancing poplar stress tolerance. Additionally, we observed that external application of low concentrations of BABA increased plant drought resistance under drought stress. Through the BABA-PtrIBIs-PtrVOZ signaling module, poplar plants were able to transduce ABA signaling and regulate their response to drought stress. These results suggest that the PtrIBI genes in poplar have the potential to improve drought tolerance in plants through the topical application of low concentrations of BABA.

Transcriptional reprogramming during recovery from drought stress in Eucalyptus grandis

The importance of drought as a constraint to agriculture and forestry is increasing with climate change. Genetic improvement of plants' resilience is one of the mitigation strategies to curb this threat. Although recovery from drought stress is important to long-term drought adaptation and has been considered as an indicator of dehydration tolerance in annual crops, this has not been well explored in forest trees. Thus, we aimed to investigate the physiological and transcriptional changes during drought stress and rewatering in Eucalyptus grandis W. Hill ex Maiden. We set up a greenhouse experiment where we imposed drought stress on 2-year-old seedlings and rewatered the recovery group after 17 days of drought. Our measurement of leaf stomatal conductance (gs) showed that, while gs was reduced by drought stress, it fully recovered after 5 days of rewatering. The RNA-seq analysis from stem samples revealed that genes related to known stress responses such as phytohormone and reactive oxygen species signaling were upregulated, while genes involved in metabolism and growth were downregulated due to drought stress. We observed reprogramming of signal transduction pathways and metabolic processes at 1 day of rewatering, indicating a quick response to rewatering. Our results suggest that recovery from drought stress may entail alterations in the jasmonic acid, salicylic acid, ethylene and brassinosteroid signaling pathways. Using co-expression network analysis, we identified hub genes, including the putative orthologs of ABI1, ABF2, ABF3, HAI2, BAM1, GolS2 and SIP1 during drought and CAT2, G6PD1, ADG1 and FD-1 during recovery. Taken together, by highlighting the molecular processes and identifying key genes, this study gives an overview of the mechanisms underlying the response of E. grandis to drought stress and recovery that trees may face repeatedly throughout their long life cycle. This provides a useful reference to the identification and further investigation of signaling pathways and target genes for future tree improvement.

Genome-Wide Analysis of the FBA Subfamily of the Poplar F-Box Gene Family and Its Role under Drought Stress

F-box proteins are important components of eukaryotic SCF E3 ubiquitin ligase complexes, which specifically determine protein substrate proteasomal degradation during plant growth and development, as well as biotic and abiotic stress. It has been found that the FBA (F-box associated) protein family is one of the largest subgroups of the widely prevalent F-box family and plays significant roles in plant development and stress response. However, the FBA gene family in poplar has not been systematically studied to date. In this study, a total of 337 F-box candidate genes were discovered based on the fourth-generation genome resequencing of P. trichocarpa. The domain analysis and classification of candidate genes revealed that 74 of these candidate genes belong to the FBA protein family. The poplar F-box genes have undergone multiple gene replication events, particularly in the FBA subfamily, and their evolution can be attributed to genome-wide duplication (WGD) and tandem duplication (TD). In addition, we investigated the P. trichocarpa FBA subfamily using the PlantGenIE database and quantitative real-time PCR (qRT-PCR); the results showed that they are expressed in the cambium, phloem and mature tissues, but rarely expressed in young leaves and flowers. Moreover, they are also widely involved in the drought stress response. At last, we selected and cloned PtrFBA60 for physiological function analysis and found that it played an important role in coping with drought stress. Taken together, the family analysis of FBA genes in P. trichocarpa provides a new opportunity for the identification of P. trichocarpa candidate FBA genes and elucidation of their functions in growth, development and stress response, thus demonstrating their utility in the improvement of P. trichocarpa.

Effect of a suitable treatment period on the genetic transformation efficiency of the plant leaf disc method

BACKGROUND

Agrobacterium tumefaciens-mediated leaf disc genetic transformation is an important way to achieve transgenics or gene editing. Ensuring stable and efficient genetic transformation is still an important problem in modern biology. It is assumed that the difference in the development status of genetic transformation cells of receptor materials is the main reason for the difference and instability of genetic transformation efficiency; the stable and efficient genetic transformation rate can be obtained by defining the appropriate treatment period of the receptor material and applying genetic transformation in a timely manner.

RESULTS

Based on these assumptions, we studied and established an efficient and stable Agrobacterium-mediated plant transformation system with hybrid poplar (Populus alba × Populus glandulosa, 84 K) leaves, stem segments and tobacco leaves as the research objects. There were differences in the development process of leaf bud primordial cells from different explants, and the genetic transformation efficiency was significantly related to the cell development stage of the in vitro cultured materials. Among them, the genetic transformation rate of poplar and tobacco leaves was the highest on the 3rd and 2nd day of culture, reaching 86.6% and 57.3%, respectively. The genetic transformation rate of poplar stem segments was the highest on the 4th day of culture, reaching 77.8%. The best treatment period was from the development of leaf bud primordial cells to the S phase of the cell cycle. The number of cells detected using flow cytometry and 5-ethynyl-2'-deoxyuridine (EdU) staining, the expression of cell cycle-related protein CDKB1; 2, CDKD1; 1, CYCA3; 4, CYCD1; 1, CYCD3; 2, CYCD6; 1, and CYCH; 1 of explants, and morphological changes of explants can be used as indicators to determine the appropriate treatment period for genetic transformation.

CONCLUSIONS

Our study provides a new and universal set of methods and characteristics to identify the S phase of the cell cycle and apply genetic transformation treatments at the appropriate time. Our results are of great significance for improving the efficiency and stability of plant leaf disc genetic transformation.

PePYL4 enhances drought tolerance by modulating water-use efficiency and ROS scavenging in Populus

Drought is one of the major limiting factors in the growth of terrestrial plants. Abscisic acid (ABA) and pyrabactin resistance 1/prabactin resistance-1 like/regulatory components of ABA receptors (PYR/PYL/RCARs) play a key role in response to drought stress. However, the underlying mechanisms of this control remain largely elusive in trees. In this study, PePYL4, a potential ortholog of the PYR/PYL/RCARs gene, was cloned from Populus euphratica. It was localized in the cytoplasm and nucleus, induced by ABA, osmotic and dehydration treatments. To study the potential biological functions of PePYL4, transgenic triploid white poplars (Populus tomentosa 'YiXianCiZhu B38') overexpressing PePYL4 were generated. PePYL4 overexpression significantly increased ABA sensitivity and reduced stomatal aperture. Compared with wild-type plants, transgenic plants had higher water-use efficiency (WUE) and lower transpiration. When exposed to drought stress, PePYL4 overexpression plants maintained higher photosynthetic activity and accumulated more biomass. Moreover, overexpression of PePYL4 improved antioxidant enzyme activity and ascorbate content to accelerate reactive oxygen species scavenging. Meanwhile, upregulation expression of the stress-related genes also contributed to improving the drought tolerance of transgenic plants. In conclusion, our data suggest that PePYL4 is a promising gene target for regulating WUE and drought tolerance in Populus.

Guard cell anion channel PbrSLAC1 regulates stomatal closure through PbrSnRK2.3 protein kinases

Stomatal pores on the leaf surface are the gateways for gas exchange between plants and the atmosphere, which is regulated mainly by the S-type anion channel SLAC1. However, the gene encoding the main S-type anion channel SLAC1 in pear and its genetic characteristics remain unknown. In this study, Pbr015894.1 was identified as the candidate for PbrSLAC1 in pear, and it was found to be expressed abundantly in leaves, particularly in the guard cells. Virus-induced gene silencing experiments indicated that stomatal closure was achieved by a change in cell turgor instigated by PbrSLAC1 channel transport of NO₃^- in pear leaves and induced by abscisic acid. Furthermore, the expression of PbrSLAC1 in Arabidopsis slac1-3 and slac1-4 rescued the defective NO₃^- transport seen in these mutants, pointing to its role in anion transport. Fluorescence microscopy suggested that PbrSLAC1 was localized in the plasma membrane, and a dual-luciferase assay system demonstrated an interaction between PbrSLAC1 and PbrSnRK2.3/2.8. Moreover, anion conductance mediated by PbrSLAC1 was activated by PbrSnRK2.3 in Xenopus laevis oocytes and the channel showed greater permeability for nitrate than chloride, sulfate, or malate ions. Taken together, these results demonstrate that PbrSLAC1, an anion channel regulated by PbrSnRK2.3, is involved in stomatal closure by mediating the efflux of NO₃^- in pear leaf.

PtoMPO1, a negative mediator, functions in poplar drought tolerance

Drought, as one of the most severe abiotic stresses in nature, adversely affects plant growth and development. Poplar is a woody plant which is prone to water-deficit sensitivity. Therefore, it is important to improve our understanding of how poplar responds to drought stress. Here, we cloned a gene from Populus tomentosa, namely PtoMPO1. PtoMPO1 encodes a DUF962 domain protein that is a homolog of yeast dioxygenase Mpo1 and Arabidopsis MHP1. The transcripts of PtoMPO1 were repressed by drought stress and ABA. Atmhp1-1 was a T-DNA insertion mutant lacking AtMHP1, and heteroexpression of PtoMPO1 in Atmhp1-1 significantly alleviated the sensitivity of Atmhp1-1 to ABA and NaCl, implying the functional replacement of PtoMPO1 to AtMHP1. PtoMPO1 overexpression decreased but PtoMPO1 mutation enhanced poplar drought tolerance. Furthermore, the expression of drought-related gene PtoRD26 is markedly lower in PtoMPO1-overexpressing plants and notably higher in Ptompo1 mutants compared to that in the wild type. Overall, these results suggested that PtoMPO1 functions as a novel negative mediator for drought tolerance in poplar.

Overexpression of PagSTOMAGEN, a Positive Regulator of Stomatal Density, Promotes Vegetative Growth in Poplar

Poplar is an important fast-growing tree, and its photosynthetic capacity directly affects its vegetative growth. Stomatal density is closely related to photosynthetic capacity and growth characteristics in plants. Here, we isolated PagSTOMAGEN from the hybrid poplar (Populus alba × Populus glandulosa) clone 84K and investigated its biological function in vegetative growth. PagSTOMAGEN was expressed predominantly in young tissues and localized in the plasma membrane. Compared with wild-type 84K poplars, PagSTOMAGEN-overexpressing plants displayed an increased plant height, leaf area, internode number, basal diameter, biomass, IAA content, IPR content, and stomatal density. Higher stomatal density improved the net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, and transpiration rate in transgenic poplar. The differential expression of genes related to stomatal development showed a diverged influence of PagSTOMAGEN at different stages of stomatal development. Finally, transcriptomic analysis showed that PagSTOMAGEN affected vegetative growth by affecting the expression of photosynthesis and plant hormone-related genes (such as SAUR75, PQL2, PSBX, ERF1, GNC, GRF5, and ARF11). Taken together, our data indicate that PagSTOMAGEN could positively regulate stomatal density and increase the photosynthetic rate and plant hormone content, thereby promoting vegetative growth in poplar. Our study is of great significance for understanding the relationship between stoma, photosynthesis, and yield breeding in poplar.

PeTGA1 enhances disease resistance against Colletotrichum gloeosporioides through directly regulating PeSARD1 in poplar

Basic leucine zipper (bZIP) proteins play important roles in responding to biotic and abiotic stresses in plants. However, the molecular mechanisms of plant resistance to pathogens remain largely unclear in poplar. The present study isolated a TGACG-binding (TGA) transcription factor, PeTGA1, from Populus euphratica. PeTGA1 belongs to subgroup D of the bZIP family and was localized to the nucleus. To study the role PeTGA1 plays in response to Colletotrichum gloeosporioides, transgenic triploid white poplars overexpressing PeTGA1 were generated. Results showed that poplars with overexpressed PeTGA1 showed a higher effective defense response to C. gloeosporioides than the wild-type plants. A yeast one-hybrid assay and an electrophoretic mobility shift assay revealed that PeTGA1 could directly bind to the PeSARD1 (P. euphratica SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1) promoter, an important regulator for salicylic acid biosynthesis. The transactivation assays indicated that PeTGA1 activated the expression of PeSARD1, and PR1 (PATHOGENESIS-RELATED 1), a SA marker gene involved in SA signaling. Subsequently, we observed that the PeTGA1 overexpression lines showed elevated SA levels, thereby resulting in the increased resistance to C. gloeosporioides. Taken together, our results indicated that PeTGA1 may exert a key role in plant immunity not only by targeting PeSARD1 thus participating in the SA biosynthesis pathway but also by involving in SA signaling via activating the expression of PR1.

Hydrogen sulfide: an emerging component against abiotic stress in plants

As a result of climate change, abiotic stresses are the most common cause of crop losses worldwide. Abiotic stresses significantly impair plants' physiological, biochemical, molecular and cellular mechanisms, limiting crop productivity under adverse climate conditions. However, plants can implement essential mechanisms against abiotic stressors to maintain their growth and persistence under such stressful environments. In nature, plants have developed several adaptations and defence mechanisms to mitigate abiotic stress. Moreover, recent research has revealed that signalling molecules like hydrogen sulfide (H₂ S) play a crucial role in mitigating the adverse effects of environmental stresses in plants by implementing several physiological and biochemical mechanisms. Mainly, H₂ S helps to implement antioxidant defence systems, and interacts with other molecules like nitric oxide (NO), reactive oxygen species (ROS), phytohormones, etc. These molecules are well-known as the key players that moderate the adverse effects of abiotic stresses. Currently, little progress has been made in understanding the molecular basis of the protective role of H₂ S; however, it is imperative to understand the molecular basis using the state-of-the-art CRISPR-Cas gene-editing tool. Subsequently, genetic engineering could provide a promising approach to unravelling the molecular basis of stress tolerance mediated by exogenous/endogenous H₂ S. Here, we review recent advances in understanding the beneficial roles of H₂ S in conferring multiple abiotic stress tolerance in plants. Further, we also discuss the interaction and crosstalk between H₂ S and other signal molecules; as well as highlighting some genetic engineering-based current and future directions.

Transcriptome Characterization of the Roles of Abscisic Acid and Calcium Signaling during Water Deficit in Garlic

Garlic (Allium sativum L.) is one of the most important vegetable crops, and breeding drought-tolerant varieties is a vital research goal. However, the underlying molecular mechanisms in response to drought stress in garlic are still limited. In this study, garlic seedlings were subjected to 15% PEG6000 for 0, 1, 4, and 12 h, respectively, to simulate drought stress. Changes of transcriptomes as a result of drought stress in garlic leaves were determined by de novo assembly using the Illumina platform. In total, 96,712 unigenes and 11,936 differentially expressed genes (DEGs) were identified in the presence of drought conditions. Transcriptome profiling revealed that the DEGs were mainly enriched in the biosynthesis of secondary metabolites, MAPK signaling pathway, starch and sucrose metabolism, phenylpropanoid biosynthesis, and plant hormone signal transduction. Genes involved in abscisic acid and calcium signaling were further investigated and discussed. Our results indicated that a coordinated interplay between abscisic acid and calcium is required for drought-induced response in garlic.

Genome-wide analysis and expression profiling of Cation/H+ exchanger (CAX) family genes reveal likely functions in cadmium stress responses in poplar

Cadmium, a toxic heavy metal, seriously affects human health and ecological security. The cation/H⁺ exchanger (CAX) family is a unique metal transporter that plays a crucial role in Cd acquisition, transfer, and remission in plants. Although there are many studies related to the genome-wide analysis of Populus trichocarpa, little research has been done on the CAX family genes, especially concerning Cd stress. In this study, genome-wide analysis of the Populus CAX family identified seven stress-related CAX genes. The evolutionary tree indicated that the CaCA family genes were grouped into four clusters. Moreover, seven pairs of genes were derived by segmental duplication in poplars. Cis-acting element analysis identified numerous stress-related elements in the promoters of diverse PtrCAXs. Furthermore, some PtrCAXs were up-regulated by drought, beetle, and mechanical damage, indicating their possible function in regulating stress response. Under cadmium stress, all CAX genes in the roots were up-regulated. Our findings suggest that plants may regulate their response to Cd stress through the TF-CAXs module. Comprehensively investigating the CAX family provides a scientific basis for the phytoremediation of heavy metal pollution by Populus.

Controlling the Gate: The Functions of the Cytoskeleton in Stomatal Movement

Stomata are specialized epidermal structures composed of two guard cells and are involved in gas and water exchange between plants and the environment and pathogen entry into the plant interior. Stomatal movement is a response to many internal and external stimuli to increase adaptability to environmental change. The cytoskeleton, including actin filaments and microtubules, is highly dynamic in guard cells during stomatal movement, and the destruction of the cytoskeleton interferes with stomatal movement. In this review, we discuss recent progress on the organization and dynamics of actin filaments and microtubule network in guard cells, and we pay special attention to cytoskeletal-associated protein-mediated cytoskeletal rearrangements during stomatal movement. We also discuss the potential mechanisms of stomatal movement in relation to the cytoskeleton and attempt to provide a foundation for further research in this field.

Genome-Wide Investigation of the PtrCHLP Family Reveals That PtrCHLP3 Actively Mediates Poplar Growth and Development by Regulating Photosynthesis

Chlorophyll (Chl) plays a crucial role in plant photosynthesis. The geranylgeraniol reductase gene (CHLP) participates in the terminal hydrogenation of chlorophyll biosynthesis. Although there are many studies related to the genome-wide analysis of Populus trichocarpa, little research has been conducted on CHLP family genes, especially those concerning growth and photosynthesis. In this study, three CHLP genes were identified in Populus. The evolutionary tree indicated that the CHLP family genes were divided into six groups. Moreover, one pair of genes was derived from segmental duplications in Populus. Many elements related to growth were detected by cis-acting element analysis of the promoters of diverse PtrCHLPs. Furthermore, PtrCHLPs exhibit different tissue expression patterns. In addition, PtrCHLP3 is preferentially expressed in the leaves and plays an important role in regulating chlorophyll biosynthesis. Silencing of PtrCHLP3 in poplar resulted in a decrease in chlorophyll synthesis in plants, thus blocking electron transport during photosynthesis. Furthermore, inhibition of PtrCHLP3 expression in poplar can inhibit plant growth through the downregulation of photosynthesis. Ultimately, PtrCHLP3 formed a co-expression network with photosynthesis and chlorophyll biosynthesis-related genes, which synergistically affected the growth and photosynthesis of poplars. Thus, this study provides genetic resources for the improved breeding of fast-growing tree traits.

Comparative analysis of the stellacyanins (SCs) family and focus on drought resistance of PtSC18 in Populus trichocarpa

Stellacyanin (SC) is a type I (blue) copper protein, which plays a crucial role in plant growth and stress response. However, the comprehensive analysis and functional research of SCs in the woody plant is still lacking. Here, a total of 74 SCs were collected and identified from Arabidopsis, papaya, grape, rice and poplar. Bioinformatics was used to analyze the gene structure, protein structure and evolutionary relationship of 74 genes, especially 19 SCs in Populus trichocarpa. Based on the RNA-seq data, expression pattern of SCs in poplar under cold, high temperature, drought and salt stress were further analyzed. Subsequently, a key candidate gene PtSC18 that strongly responded to drought stress was screened. Subcellular localization experiment exhibited that PtSC18 was localized in the nucleus and plasma membrane. Overexpression of PtSC18 enhanced drought tolerance of transgenic Arabidopsis by improving water retention and reducing oxidative damage. Measurements of physiological indicators, including chlorophyll, H₂O₂, malondialdehyde content, peroxidase and catalase enzyme activities and electrical conductivity, all supported this conclusion. More importantly, PtSC18 enhanced the expression of some stress-related genes in transgenic Arabidopsis. Overall, our results lay a foundation for understanding the structure and function of PtSCs and provide useful gene resources for breeding through genetic engineering.

Genome-wide investigation and expression profiling of polyphenol oxidase (PPO) family genes uncover likely functions in organ development and stress responses in Populus trichocarpa

Background

Trees such as Populus are planted extensively for reforestation and afforestation. However, their successful establishment greatly depends upon ambient environmental conditions and their relative resistance to abiotic and biotic stresses. Polyphenol oxidase (PPO) is a ubiquitous metalloproteinase in plants, which plays crucial roles in mediating plant resistance against biotic and abiotic stresses. Although the whole genome sequence of Populus trichocarpa has long been published, little is known about the PPO genes in Populus, especially those related to drought stress, mechanical damage, and insect feeding. Additionally, there is a paucity of information regarding hormonal responses at the whole genome level.

Results

A genome-wide analysis of the poplar PPO family was performed in the present study, and 18 PtrPPO genes were identified. Bioinformatics and qRT-PCR were then used to analyze the gene structure, phylogeny, chromosomal localization, gene replication, cis-elements, and expression patterns of PtrPPOs. Sequence analysis revealed that two-thirds of the PtrPPO genes lacked intronic sequences. Phylogenetic analysis showed that all PPO genes were categorized into 11 groups, and woody plants harbored many PPO genes. Eighteen PtrPPO genes were disproportionally localized on 19 chromosomes, and 3 pairs of segmented replication genes and 4 tandem repeat genomes were detected in poplars. Cis-acting element analysis identified numerous growth and developmental elements, secondary metabolism processes, and stress-related elements in the promoters of different PPO members. Furthermore, PtrPPO genes were expressed preferentially in the tissues and fruits of young plants. In addition, the expression of some PtrPPOs could be significantly induced by polyethylene glycol, abscisic acid, and methyl jasmonate, thereby revealing their potential role in regulating the stress response. Currently, we identified potential upstream TFs of PtrPPOs using bioinformatics.

Conclusions

Comprehensive analysis is helpful for selecting candidate PPO genes for follow-up studies on biological function, and progress in understanding the molecular genetic basis of stress resistance in forest trees might lead to the development of genetic resources.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08028-9.

NAC Transcription Factor PwNAC11 Activates ERD1 by Interaction with ABF3 and DREB2A to Enhance Drought Tolerance in Transgenic Arabidopsis

NAC (NAM, ATAF1/2, and CUC2) transcription factors are ubiquitously distributed in eukaryotes and play significant roles in stress response. However, the functional verifications of NACs in Picea (P.) wilsonii remain largely uncharacterized. Here, we identified the NAC transcription factor PwNAC11 as a mediator of drought stress, which was significantly upregulated in P. wilsonii under drought and abscisic acid (ABA) treatments. Yeast two-hybrid assays showed that both the full length and C-terminal of PwNAC11 had transcriptional activation activity and PwNAC11 protein cannot form a homodimer by itself. Subcellular observation demonstrated that PwNAC11 protein was located in nucleus. The overexpression of PwNAC11 in Arabidopsis obviously improved the tolerance to drought stress but delayed flowering time under nonstress conditions. The steady-state level of antioxidant enzymes' activities and light energy conversion efficiency were significantly increased in PwNAC11 transgenic lines under dehydration compared to wild plants. PwNAC11 transgenic lines showed hypersensitivity to ABA and PwNAC11 activated the expression of the downstream gene ERD1 by binding to ABA-responsive elements (ABREs) instead of drought-responsive elements (DREs). Genetic evidence demonstrated that PwNAC11 physically interacted with an ABA-induced protein-ABRE Binding Factor3 (ABF3)-and promoted the activation of ERD1 promoter, which implied an ABA-dependent signaling cascade controlled by PwNAC11. In addition, qRT-PCR and yeast assays showed that an ABA-independent gene-DREB2A-was also probably involved in PwNAC11-mediated drought stress response. Taken together, our results provide the evidence that PwNAC11 plays a dominant role in plants positively responding to early drought stress and ABF3 and DREB2A synergistically regulate the expression of ERD1.

Analysis of Populus glycosyl hydrolase family I members and their potential role in the ABA treatment and drought stress response

Glycoside hydrolase family 1 (GH1) β-glucosidases (BGLUs) are encoded by a large number of genes and are involved in many developmental processes and stress responses in plants. Due to their importance in plant growth and development, genome-wide analyses have been conducted in the model plant species Arabidopsis thaliana, rice and maize but not in woody plant species, which have important economic and ecological value. In this study, we systematically analyzed Populus BGLUs (PtBGLUs) and demonstrated the involvement of several genes under stress conditions. Forty-four PtBGLUs were identified in Populus databases; these genes were located on 11 chromosomes, and the proteins of several PtBGLU genes were highly similar. More than 90% of PtBGLUs contain three conserved motifs. Collinearity results showed that 44 PtBGLU genes resulted from 12 tandem and 5 segmental duplication events. Phylogenetic analysis revealed that 128 BGLU genes from Populus trichocarpa, A. thaliana and Oryza sativa could be classified into 4 subgroups and subgroup Ⅱ and Ⅳ were differently having PtBGLUs and AtBGLUs. We further investigated whether several PtBGLUs responded to drought stress and ABA treatment, and the results showed that most of the selected BGLU genes were expressed in response to stress, which is consistent with previous studies involving rice and Arabidopsis homologous genes. Large numbers of stress-, hormone-, and development-related elements in the PtBGLU promoters suggest that BGLU genes may be involved in complex networks. Taken together, our results provide valuable information for an improved understanding of β-glucosidase function in woody plants.

Genome-Wide Investigation of the NF-X1 Gene Family in Populus trichocarpa Expression Profiles during Development and Stress

Poplar are planted extensively in reforestation and afforestation. However, their successful establishment largely depends on the environmental conditions of the newly established plantation and their resistance to abiotic as well as biotic stresses. NF-X1, a widespread transcription factor in plants, plays an irreplaceable role in plant growth, development, and stress tolerance. Although the whole genome sequence of Populus trichocarpa has been published for a long time, little is known about the NF-X1 genes in poplar, especially those related to drought stress, mechanical damage, insect feeding, and hormone response at the whole genome level. In this study, whole genome analysis of the poplar NF-X1 family was performed, and 4 PtrNF-X1 genes were identified. Then, bioinformatics analysis and qRT-PCR were applied to analyze the gene structure, phylogeny, chromosomal localization, gene replication, Cis-elements, and expression patterns of PtrNF-X1genes. Sequence analysis revealed that one-quarter of the PtrNF-X1 genes did not contain introns. Phylogenetic analysis revealed that all NF-X1 genes were split into three subfamilies. The number of two pairs of segmented replication genes were detected in poplars. Cis-acting element analysis identified a large number of elements of growth and development and stress-related elements on the promoters of different NF-X1 members. In addition, some PtrNF-X1 could be significantly induced by polyethylene glycol (PEG) and abscisic acid (ABA), thus revealing their potential role in regulating stress response. Comprehensive analysis is helpful in selecting candidate NF-X1 genes for the follow-up study of the biological function, and molecular genetic progress of stress resistance in forest trees provides genetic resources.

Transcriptional Regulation of Drought Response in Arabidopsis and Woody Plants

Within the context of global warming, long-living plants such as perennial woody species endure adverse conditions. Among all of the abiotic stresses, drought stress is one of the most detrimental stresses that inhibit plant growth and productivity. Plants have evolved multiple mechanisms to respond to drought stress, among which transcriptional regulation is one of the key mechanisms. In this review, we summarize recent progress on the regulation of drought response by transcription factor (TF) families, which include abscisic acid (ABA)-dependent ABA-responsive element/ABRE-binding factors (ABRE/ABF), WRKY, and Nuclear Factor Y families, as well as ABA-independent AP2/ERF and NAC families, in the model plant Arabidopsis. We also review what is known in woody species, particularly Populus, due to its importance and relevance in economic and ecological processes. We discuss opportunities for a deeper understanding of drought response in woody plants with the development of high-throughput omics analyses and advanced genome editing techniques.