Expression analysis of the BpARF genes in Betula platyphylla under drought stress

Enigmatic role of auxin response factors in plant growth and stress tolerance

Abiotic and biotic stresses globally constrain plant growth and impede the optimization of crop productivity. The phytohormone auxin is involved in nearly every aspect of plant development. Auxin acts as a chemical messenger that influences gene expression through a short nuclear pathway, mediated by a family of specific DNA-binding transcription factors known as Auxin Response Factors (ARFs). ARFs thus act as effectors of auxin response and translate chemical signals into the regulation of auxin responsive genes. Since the initial discovery of the first ARF in Arabidopsis, advancements in genetics, biochemistry, genomics, and structural biology have facilitated the development of models elucidating ARF action and their contributions to generating specific auxin responses. Yet, significant gaps persist in our understanding of ARF transcription factors despite these endeavors. Unraveling the functional roles of ARFs in regulating stress response, alongside elucidating their genetic and molecular mechanisms, is still in its nascent phase. Here, we review recent research outcomes on ARFs, detailing their involvement in regulating leaf, flower, and root organogenesis and development, as well as stress responses and their corresponding regulatory mechanisms: including gene expression patterns, functional characterization, transcriptional, post-transcriptional and post- translational regulation across diverse stress conditions. Furthermore, we delineate unresolved questions and forthcoming challenges in ARF research.

Genome-wide identification and expression analysis of ARF gene family in embryonic development of Korean pine (Pinus koraiensis)

BACKGROUND

The Auxin Responsive Factor (ARF) family plays a crucial role in mediating auxin signal transduction and is vital for plant growth and development. However, the function of ARF genes in Korean pine (Pinus koraiensis), a conifer species of significant economic value, remains unclear.

RESULTS

This study utilized the whole genome of Korean pine to conduct bioinformatics analysis, resulting in the identification of 13 ARF genes. A phylogenetic analysis revealed that these 13 PkorARF genes can be classified into 4 subfamilies, indicating the presence of conserved structural characteristics within each subfamily. Protein interaction prediction indicated that Pkor01G00962.1 and Pkor07G00704.1 may have a significant role in regulating plant growth and development as core components of the PkorARFs family. Additionally, the analysis of RNA-seq and RT-qPCR expression patterns suggested that PkorARF genes play a crucial role in the development process of Korean pine.

CONCLUSION

Pkor01G00962.1 and Pkor07G00704.1, which are core genes of the PkorARFs family, play a potentially crucial role in regulating the fertilization and developmental process of Korean pine. This study provides a valuable reference for investigating the molecular mechanism of embryonic development in Korean pine and establishes a foundation for cultivating high-quality Korean pine.

An efficient screening system of disease-resistant genes from wild apple, Malus sieversii in response to Valsa mali pathogenic fungus

For molecular breeding of future apples, wild apple (Malus sieversii), the primary progenitor of domesticated apples, provides abundant genetic diversity and disease-resistance traits. Valsa canker (caused by the fungal pathogen Valsa mali) poses a major threat to wild apple population as well as to cultivated apple production in China. In the present study, we developed an efficient system for screening disease-resistant genes of M. sieversii in response to V. mali. An optimal agrobacterium-mediated transient transformation of M. sieversii was first used to manipulate in situ the expression of candidate genes. After that, the pathogen V. mali was inoculated on transformed leaves and stems, and 3 additional methods for slower disease courses were developed for V. mali inoculation. To identify the resistant genes, a series of experiments were performed including morphological (incidence, lesion area/length, fungal biomass), physiological (H2O2 content, malondialdehyde content), and molecular (Real-time quantitative Polymerase Chain Reaction) approaches. Using the optimized system, we identified two transcription factors with high resistance to V. mali, MsbHLH41 and MsEIL3. Furthermore, 35 and 45 downstream genes of MsbHLH41 and MsEIL3 were identified by screening the V. mali response gene database in M. sieversii, respectively. Overall, these results indicate that the disease-resistant gene screening system has a wide range of applications for identifying resistant genes and exploring their immune regulatory networks.

Effects of PmaIAA27 and PmaARF15 genes on drought stress tolerance in pinus massoniana

BACKGROUND

Auxin plays an important role in plant resistance to abiotic stress. The modulation of gene expression by Auxin response factors (ARFs) and the inhibition of auxin/indole-3-acetic acid (Aux/IAA) proteins play crucial regulatory roles in plant auxin signal transduction. However, whether the stress resistance of Masson pine (Pinus massoniana), as a representative pioneer species, is related to Aux/IAA and ARF genes has not been thoroughly studied and explored.

RESULTS

The present study provides preliminary evidence for the regulatory role of the PmaIAA27 gene in abiotic stress response in Masson pine. We investigated the effects of drought and hormone treatments on Masson pine by examining the expression patterns of PmaIAA27 and PmaARF15 genes. Subsequently, we conducted gene cloning, functional testing using transgenic tobacco, and explored gene interactions. Exogenous auxin irrigation significantly downregulated the expression of PmaIAA27 while upregulating PmaARF15 in Masson pine seedlings. Moreover, transgenic tobacco with the PmaIAA27 gene exhibited a significant decrease in auxin content compared to control plants, accompanied by an increase in proline content - a known indicator of plant drought resistance. These findings suggest that overexpression of the PmaIAA27 gene may enhance drought resistance in Masson pine. To further investigate the interaction between PmaIAA27 and PmaARF15 genes, we performed bioinformatics analysis and yeast two-hybrid experiments which revealed interactions between PB1 structural region of PmaARF15 and PmaIAA27.

CONCLUSION

The present study provides new insights into the regulatory functions of Aux/IAA and ARF genes in Masson pine. Overexpression of PmaIAA gene may have negative effects on the growth of Masson pine, but may improve the drought resistance. Therefore, this study has great application prospects.

Characterization of the gene expression profile response to drought stress in Haloxylon using PacBio single-molecule real-time and Illumina sequencing

Haloxylon ammodendron and Haloxylon persicum are important drought-tolerant plants in northwest China. The whole-genome sequencing of H. ammodendron and H. persicum grown in their natural environment is incomplete, and their transcriptional regulatory network in response to drought environment remains unclear. To reveal the transcriptional responses of H. ammodendron and H. persicum to an arid environment, we performed single-molecule real-time (SMRT) and Illumina RNA sequencing. In total, 20,246,576 and 908,053 subreads and 435,938 and 210,334 circular consensus sequencing (CCS) reads were identified by SMRT sequencing of H. ammodendron and H. persicum, and 15,238 and 10,135 unigenes, respectively, were successfully obtained. In addition, 9,794 and 7,330 simple sequence repeats (SSRs) and 838 and 71 long non-coding RNAs were identified. In an arid environment, the growth of H. ammodendron was restricted; plant height decreased significantly; basal and branch diameters became thinner and hydrogen peroxide (H₂O₂) content and peroxidase (POD) activity were increased. Under dry and wet conditions, 11,803 and 15,217 differentially expressed genes (DEGs) were identified in H. ammodendron and H. persicum, respectively. There were 319 and 415 DEGs in the signal transduction pathways related to drought stress signal perception and transmission, including the Ca²⁺ signal pathway, the ABA signal pathway, and the MAPK signal cascade. In addition, 217 transcription factors (TFs) and 398 TFs of H. ammodendron and H. persicum were differentially expressed, including FAR1, MYB, and AP2/ERF. Bioinformatic analysis showed that under drought stress, the expression patterns of genes related to active oxygen [reactive oxygen species (ROS)] scavenging, functional proteins, lignin biosynthesis, and glucose metabolism pathways were altered. Thisis the first full-length transcriptome report concerning the responses of H. ammodendron and H. persicum to drought stress. The results provide a foundation for further study of the adaptation to drought stress. The full-length transcriptome can be used in genetic engineering research.

Chinese Cherry (Cerasus pseudocerasus Lindl.) ARF7 Participates in Root Development and Responds to Drought and Low Phosphorus

In this paper, an auxin-responsive transcription factor, CpARF7, was isolated from the roots of Chinese cherry (Cerasus pseudocerasus Lindl. Cv. “Manao Hong”). CpARF7 is highly homologous to AtARF7 or AtARF19 in Arabidopsis, and PavARF1 or PavARF14 in sweet cherry. However, in the phenotype of transgenic tomatoes, the root morphology changed, the main root elongated, and the lateral root increased. Both drought treatment and low-phosphorus conditions can elongate the roots of transgenic tomatoes. In addition, the drought resistance and low-phosphorus tolerance of the transgenic lines are improved, and the POD, SOD, and CAT activities under drought and low-phosphorus environments are increased. There is an effect on the tomato somatotropin suppressor gene, SlIAAs, in which SlIAA1/14/19/29 are up-regulated and SlIAA2/11/12/16 are down-regulated. These results indicate that CpARF7 plays an essential regulatory role in root formation and abiotic stress response, and deepens the understanding of auxin-responsive genes in root growth and abiotic stress.

Functional roles of the birch BpRAV1 transcription factor in salt and osmotic stress response

RAV (Related to ABI3/VP1) transcription factors play vital roles in regulating plant response to abiotic stresses; however, the regulatory mechanisms underlying stress response are still poorly understood for most of the RAVgenes. In this study, a novel gene BpRAV1 was cloned from white birch (Betula platyphylla). BpRAV1 protein is localized in the nucleus and serves as a transcriptional activator. The expression of BpRAV1 was induced by salt and osmotic stress treatments. BpRAV1-overexpression birch seedlings exhibited dramatically less ROS accumulation and reduced cell death in response to salt and osmotic stresses. BpRAV1 can specifically bind to the known RAV1A element. In addition, a novel cis-acting element (termed RBS1) bound by BpRAV1 was identified by transcription factor (TF)- centered Y1H assay. BpRAV1 activated the RAV1A and RBS1 elements to induce the expression of SOD and POD genes, resulting in increased SOD and POD activities to enhance ROS scavenging ability, thus improving salt and osmotic stress tolerance. These results indicate that BpRAV1 is a positive regulator governing abiotic stress response.

PopW enhances drought stress tolerance of alfalfa via activating antioxidative enzymes, endogenous hormones, drought related genes and inhibiting senescence genes

Alfalfa (Medicago sativa L.) has the advantages of high yield and nutritional value as a perennial forage. However, one of the drawbacks of alfalfa is its susceptibility to drought conditions, which is a global problem in agriculture. The purpose of this study was to reveal the effects of exogenous PopW, a harpin protein from Ralstonia solanacearum, treatment on growth parameters, physiological and biochemical mechanism of alfalfa under drought-stress conditions. Growth parameters, relative water content, free proline, leaf area, total chlorophyll, antioxidative enzymes, endogenous hormones including ABA, CTK, GA, JA, SA and IAA were determined in response to exogenous PopW treatment under drought stress in alfalfa cultivar (Victoria). Moreover, relative gene expressions of drought-related and leaf senescence genes were determined. Under drought stress, alfalfa plants had lower shoot dry weight, shoot length, relative water content, leaf area, and total chlorophyll content, compared to control (non-stressed). However, Exogenous PopW treatment significantly increased growth values, relative water content, free proline, leaf area, total chlorophyll content, catalase, glutathione reductase and superoxide dismutase under drought conditions, compared to control and drought stress alone. Moreover, exogenous PopW treatment significantly increased ABA, GA, JA, SA, IAA contents, up-regulated auxin- and drought-responsive genes, down-regulated leaf senescence genes. Exogenous PopW treatment enhanced drought stress tolerance of alfalfa due to changes of endogenous hormone contents and expression levels of drought stress and leaf senescence genes. The results of the study show that PopW treatment could be used to increase the forage yield of alfalfa on areas having drought problem.

Heterotrimeric G-protein γ subunits regulate ABA signaling in response to drought through interacting with PP2Cs and SnRK2s in mulberry (Morus alba L.)

ABA signaling plays a central role in regulating plants respond to drought. Although much progress has been made in understanding the functions of ABA signaling in drought response, very little information is available regarding woody plants. In this study, the components of ABA signaling pathway were identified in mulberry which has excellent adaptation to drought, including three PYLs, two PP2Cs, two SnRK2s, four ABFs, and an ABA responsive gene MaRD29B. The gene expression of ABA signaling components exhibited significant response to ABA and drought, and their roles in drought response were revealed using a transient transformation system in mulberry seedlings. We discovered the ABA signaling components, MaABI1/2 and MaSnRK2.1/2.4, could directly interact with G-protein γ subunits, MaGγ1 and MaGγ2, which indicated that G-protein γ subunits may mediate the signal crosstalk between G-proteins and ABA signaling. Transient activation assay in tobacco and RNAi silencing assay in mulberry further demonstrated that MaGγ1 and MaGγ2 regulated drought response by enhancing ABA signaling. This study expands the repertoire of ABA signaling controlling drought responses in plants and provides the direct evidence about the crosstalk between ABA signaling and G-proteins for the first time.

Characterization and analysis of the transcriptome response to drought in Larix kaempferi using PacBio full-length cDNA sequencing integrated with de novo RNA-seq reads

A hypothetical model of drought tolerance mechanism of Larix kaempferi was established through SMRT-seq and Illumina HiSeq. Larix kaempferi is an important economic and ecological species and a major afforestation species in north-eastern China. To date, no information has been reliably derived regarding full-length cDNA sequencing information on L. kaempferi. By single-molecule long-read isoform sequencing (SMRT-seq), here we report a total of 26,153,342 subreads (21.24 Gb) and 330,371 circular consensus sequence (CCS) reads after the modification of site mismatch, and 35,414 unigenes were successfully collected. To gain deeper insights into the molecular mechanisms of L. kaempferi response to drought stress, we combined Illumina HiSeq with SMRT-seq to decode full-length transcripts. In this study, we report 27 differentially expressed genes (DEGs) involved in the perception and transmission of drought stress signals in L. kaempferi. A large number of DEGs responding to drought stress were detected in L. kaempferi, especially DEGs involved in the reactive oxygen species (ROS) scavenging, lignin biosynthesis, and sugar metabolism, and DEGs encoding drought stress proteins. We detected 73 transcription factors (TFs) under drought stress, including AP2/ERF, bZIP, TCP, and MYB. This study provides basic full sequence resources for L. kaempferi research and will help us to better understand the functions of drought-resistance genes in L. kaempferi.