Enhanced tolerance to drought stress resulting from Caragana korshinskii CkWRKY33 in transgenic Arabidopsis thaliana

Multiple functions and regulatory networks of WRKY33 and its orthologs

Arabidopsis thaliana WRKY33 is currently one of the most studied members of the Group I WRKY transcription factor family. Research has confirmed that WRKY33 is involved in the regulation of various biological and abiotic stresses and occupies a central position in the regulatory network. The functional studies of orthologous genes of WRKY33 from other species are also receiving increasing attention. In this article, we summarized thirty-eight orthologous genes of AtWKRY33 from twenty-five different species. Their phylogenetic relationship and conserved WRKY domain were analyzed and compared. Similar to AtWKRY33, the well-studied orthologous gene members from rice and tomato also have multiple functions. In addition to playing important regulatory roles in responding to their specific pathogens, they are also involved in regulating various abiotic stresses and development. AtWKRY33 exerts its multiple functions through a complex regulatory network. Upstream transcription factors or other regulatory factors activate or inhibit the expression of AtWKRY33 at the chromatin and transcriptional levels. Interacting proteins affect the transcriptional activity of AtWKRY33 through phosphorylation, ubiquitination, SUMOylation, competition, or cooperation. The downstream genes are diverse and include three major categories: transcription factors, synthesis, metabolism, and signal transduction of various hormones, and disease resistance genes. In the regulatory network of AtWRKY33 orthologs, many conserved regulatory characteristics have been discovered, such as self-activation and phosphorylation by MAP kinases. This can provide a comparative reference for further studying the functions of other orthologous genes of AtWKRY33.

Genome-Wide Analysis of WRKY Transcription Factors Involved in Abiotic Stress and ABA Response in Caragana korshinskii

The WRKY transcription factor family plays a vital role in plant development and environmental response. However, the information of WRKY genes at the genome-wide level is rarely reported in Caragana korshinskii. In this study, we identified and renamed 86 CkWRKY genes, which were further classified into three groups through phylogenetic analysis. Most of these WRKY genes were clustered and distributed on eight chromosomes. Multiple sequence alignment revealed that the conserved domain (WRKYGQK) of the CkWRKYs was basically consistent, but there were also six variation types (WRKYGKK, GRKYGQK, WRMYGQK, WRKYGHK, WKKYEEK and RRKYGQK) that appeared. The motif composition of the CkWRKYs was quite conservative in each group. In general, the number of WRKY genes gradually increased from lower to higher plant species in the evolutionary analysis of 28 species, with some exceptions. Transcriptomics data and RT-qPCR analysis showed that the CkWRKYs in different groups were involved in abiotic stresses and ABA response. Our results provided a basis for the functional characterization of the CkWRKYs involved in stress resistance in C. korshinskii.

Transcriptome analysis of auxin transcription factor OsARF17-mediated rice stripe mosaic virus response in rice

Introduction

Plant auxin response factors (ARFs) play an irreplaceable role in regulating the expression of auxin response genes. Our previous studies have indicated that auxin response factor OsARF17 plays a crucial role in plant defense against diverse rice viruses.

Methods

Utilizing a comparative transcriptome analysis of Rice stripe mosaic virus (RSMV)-inoculated OsARF17 mutant rice plants, to further elucidate the molecular mechanism of OsARF17 in antiviral defense pathway.

Results

KEGG enrichment analyses showed that the down-regulated differentially expressed genes (DEGs) belonged to plant-pathogen interaction and plant hormone signal transduction pathways were markedly enriched in OsARF17 mutants under RSMV inoculation. Furthermore, Gene ontology (GO) analyses revealed that these genes were enriched in a variety of hormone biosynthetic process, including jasmonic acid (JA), auxin, and abscisic acid (ABA). RT-qPCR assays showed that the induction of plant defense-related genes, such as WRKY transcription factors, OsAHT2 and OsDR8, and JA-related genes, were significantly suppressed in OsARF17 mutants in response to RSMV.

Discussion

Our study reveals that OsARF17-mediated antiviral immunity may be achieved through affecting the interaction between different phytohormones and regulating defense gene expression in rice. This study provides new insights into the molecular mechanisms of auxin signaling in the rice-virus interaction.

The bacterial consortia promote plant growth and secondary metabolite accumulation in Astragalus mongholicus under drought stress

Astragalus mongholicus is a widely used Traditional Chinese Medicine. However, cultivated A. mongholicus is often threatened by water shortage at all growth stage, and the content of medicinal compounds of cultivated A. mongholicus is much lower than that of wild plants. To alleviate drought stress on A. mongholicus and improve the accumulation of medicinal components in roots of A. mongholicus, we combined different bacteria with plant growth promotion or abiotic stress resistance characteristics and evaluated the role of bacterial consortium in helping plants tolerate drought stress and improving medicinal component content in roots simultaneously. Through the determination of 429 bacterial strains, it was found that 97 isolates had phosphate solubilizing ability, 63 isolates could release potassium from potash feldspar, 123 isolates could produce IAA, 58 isolates could synthesize ACC deaminase, and 21 isolates could secret siderophore. Eight bacterial consortia were constructed with 25 bacterial isolates with more than three functions or strong growth promoting ability, and six out of eight bacterial consortia significantly improved the root dry weight. However, only consortium 6 could increase the root biomass, astragaloside IV and calycosin-7-glucoside content in roots simultaneously. Under drought challenge, the consortium 6 could still perform these functions. Compared with non-inoculated plants, the root dry weight of consortium inoculated-plants increased by 120.0% and 78.8% under mild and moderate drought stress, the total content of astragaloside IV increased by 183.83% and 164.97% under moderate and severe drought stress, calycosin-7-glucoside content increased by 86.60%, 148.56% and 111.45% under mild, moderate and severe drought stress, respectively. Meanwhile, consortium inoculation resulted in a decrease in MDA level, while soluble protein and proline content and SOD, POD and CAT activities increased. These findings provide novel insights about multiple bacterial combinations to improve drought stress responses and contribute to accumulate more medicinal compounds.

Drought-responsive WRKY transcription factor genes IgWRKY50 and IgWRKY32 from Iris germanica enhance drought resistance in transgenic Arabidopsis

Drought greatly affects the growth and development of garden plants and affects their ornamental value. WRKY transcription factors make up one of the largest transcription factor families in plants and they play an important role in the plant response to drought stress. However, the function of the WRKY gene in response to drought stress in Iris germanica, which is commonly used in landscaping, has not been studied. In this study, we isolated two WRKY transcription factor genes from Iris germanica, IgWRKY50 and IgWRKY32, which belong to Group II and Group III of the WRKY family, respectively. IgWRKY50 and IgWRKY32 could be induced by PEG-6000, high temperature and ABA in Iris germanica. IgWRKY50 and IgWRKY32 could quickly respond to drought and they peaked at 3 h after PEG-6000 treatment (19.93- and 23.32-fold). The fusion proteins IgWRKY50-GFP and IgWRKY32-GFP were located in the nucleus of mesophyll protoplasts of Arabidopsis. The overexpression of the IgWRKY50 and IgWRKY32 genes improved the osmotic tolerance of transgenic Arabidopsis, mainly exhibited by the transgenic plants having a higher germination rate and a longer total root length on 1/2 MS medium containing mannitol. Under PEG-6000 stress, the transgenic plants had higher stomatal closure than the wild type (WT). Under natural drought stress, the water loss rate of the isolated leaves of transgenic Arabidopsis was lower than that of WT, the contents of proline (Pro) and soluble protein (SP) and the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the transgenic plants were higher, but the content of malondialdehyde (MDA) was lower. Furthermore, the expression of several stress-related genes (RD29A, DREB2A, PP2CA, and ABA2) was significantly increased in IgWRKY50- and IgWRKY32- overexpressing transgenic Arabidposis plants after drought treatment. These results suggest that IgWRKY50 and IgWRKY32, as two positive regulators, enhance the drought resistance of transgenic Arabidopsis by mediating the ABA signal transduction pathway. IgWRKY50 and IgWRKY32 can be used as candidate genes for molecular breeding of drought resistance in Iris.

Identification of WRKY transcription factor family genes in Pinus massoniana Lamb. and their expression patterns and functions in response to drought stress

BACKGROUND

Pinus massoniana Lamb. is the timber species with the widest distribution and the largest afforestation area in China, providing a large amount of timber, turpentine and ecological products. Seasonal drought caused by climate warming severely constrains the quality and growth of P. massoniana forests. WRKY transcription factors play an important role in plant responses to abiotic stress. In this study, the molecular mechanisms by which P. massoniana responds to drought stress were analysed based on the P. massoniana WRKY (PmWRKY) family of genes.

RESULTS

Forty-three PmWRKYs are divided into three major families, 7 sub-families, and the conserved motifs are essentially the same. Among these 43 PmWRKYs express under drought stress but with different expression patterns in response to stress. PmWRKYs respond to drought stress induced by exogenous hormones of SA, ABA, and MeJA. The expression of PmWRKY6, PmWRKY10, and PmWRKY30 up-regulate in different families and tissues under drought stress, while PmWRKY22 down-regulate. Transgenetic tobaccos of PmWRKY31 are with lower malondialdehyde (MDA) content and higher proline (Pro) content than wild type (WT) tobaccos. In transgenic tobaccos of PmWRKY31, expression levels of related genes significantly improve, and drought tolerance enhance.

CONCLUSIONS

This study analysed the molecular biological characteristics of PmWRKYs and investigated the expression patterns and functions of PmWRKYs in response to drought stress in P. massoniana. The results of this study provide a basis for in-depth research of the molecular functions of PmWRKYs in response to drought stress.

Identification of drought responsive Elaeis guineensis WRKY transcription factors with sensitivity to other abiotic stresses and hormone treatments

BACKGROUND

The ability of plants to withstand and thrive in an adverse environment is crucial to ensure their survivability and yield performance. The WRKY transcription factors (TFs) have crucial roles in plant growth, development and stress response, particularly drought stress. In oil palm, drought is recognized as one of the major yield limiting factors. However, the roles of WRKY TFs in the drought response of oil palm is unclear.

RESULTS

Herein, we studied the transcriptome of drought treated oil palm leaf and identified 40 differentially expressed genes (DEGs) of WRKY TFs, of which 32 DEGs were upregulated and 8 DEGs were downregulated in response to drought stress in oil palm. They were categorized into Groups I to IV based on the numbers of WRKY domain and the structural difference in the zinc finger domain. Multiple stress- and hormone-responsive cis-regulatory elements were detected in the drought responsive oil palm EgWRKY (Dro-EgWRKY) genes. Fourteen of the 15 selected oil palm WRKY (EgWRKY) genes demonstrated a tissue-specific expression profile except for EgWRKY28 (Group I), which was expressed in all tissues tested. The expression levels of 15 candidate EgWRKYs were upregulated upon salinity and heat treatments, while several genes were also inducible by abscisic acid, methyl jasmonate, salicylic acid and hydrogen peroxide treatments. Members of the Group III WRKY TFs including EgWRKY07, 26, 40, 52, 59, 73 and 81 displayed multiple roles in drought- and salinity-response under the modulation of phytohormones.

CONCLUSIONS

EgWRKY TFs of oil palm are involved in phytohormones and abiotic stress responses including drought, salinity and heat. EgWRKY07, 26, 59 and 81 from Group III maybe important regulators in modulating responses of different abiotic stresses. Further functional analysis is required to understand the underlying mechanism of WRKY TFs in the regulatory network of drought stress.