The sucrose non-fermentation-related protein kinase (SnRK) is a kind of Ser/Thr protein kinase, which plays a crucial role in plant stress response by phosphorylating the target protein to regulate the interconnection of various signaling pathways. However, little is known about the SnRK family in Eucalyptus grandis. Thirty-four putative SnRK sequences were identified in E. grandis and divided into three subgroups (SnRK1, SnRK2 and SnRK3) based on phylogenetic analysis and the type of domain. Chromosome localization showed that SnRK family members are unevenly distributed in the remaining 10 chromosomes, with the notable exception of chromosome 11. Gene structure analysis reveal that 10 of the 24 SnRK3 genes contained no introns. Moreover, conserved motif analyses showed that SnRK sequences belonged to the same subgroup that contained the same motif type of motif. The Ka/Ks ratio of 17 paralogues suggested that the EgrSnRK gene family underwent a purifying selection. The upstream region of EgrSnRK genes enriched with different type and numbers of cis-elements indicated that EgrSnRK genes are likely to play a role in the response to diverse stresses. Quantitative real-time PCR showed that the majority of the SnRK genes were induced by salt treatment. Genome-wide analyses and expression pattern analyses provided further understanding on the function of the SnRK family in the stress response to different environmental salt concentrations.

Brassinosteroids (BRs) are a group of plant hormones which play a pivotal role in modulating cell elongation, stress responses, vascular differentiation and senescence. In response to BRs, BRASSINAZOLE-RESISTANT (BZR) transcription factors (TFs) accumulate in the nucleus, where they modulate thousands of target genes and coordinate many biological processes, especially in regulating defense against biotic and abiotic stresses. In this study, 6 BZR TFs of () from a genome-wide survey were characterized by sequence analysis and expression profiling against several abiotic stresses. The results showed that BZR gene family in was slightly smaller compared to and , but all phylogenetic groups were represented. Various systematic in silico analysis of these TFs validated the basic properties of BZRs, whereas comparative studies showed a high degree of similarity with recognized BZRs of other plant species. In the organ-specific expression analyses, 4 were expressed in vascular tissue indicating their possible functions in wood formation. Meanwhile, almost all genes showed differential transcript abundance levels in response to exogenously applied BR, MeJA, and SA, and salt and cold stresses. Besides, protein interaction analysis showed that all genes were associated with BR signaling directly or indirectly. These TFs were proposed as transcriptional activators or repressors of abiotic stress response and growth and development pathways of by participating in BR signaling processes. These findings would be helpful in resolving the regulatory mechanism of in stress resistance conditions but require further functional study of these potential TFs in .

Gibberellins (GAs) play a key role in plant growth and development including cell elongation, cell expansion, and xylem differentiation. Eucalyptus are the world's most widely planted hardwood trees providing fiber and energy. However, the roles of GAs in Eucalyptus remain unclear and their effects on xylem development remain to be determined. In this study, E. grandis plants were treated with 0.10 mg L GA and/or paclobutrazol (PAC, a GA inhibitor). The growth of shoot and root were recorded, transverse sections of roots and stems were stained using toluidine blue, and expression levels of genes related to hormone response and secondary cell wall biosynthesis were analyzed by quantitative real-time PCR. The results showed that GA dramatically promoted the length of shoot and root, but decreased the diameter of root and stem. Exogenous GA application also significantly promoted xylem development in both stem and root. Expression analysis revealed that exogenous GA application altered the transcript levels of genes related to the GA biosynthetic pathway and GA signaling, as well as genes related to auxin, cytokinin, and secondary cell wall. These findings suggest that GAs may interact with other hormones (such as auxin and cytokinin) to regulate the expression of secondary cell wall biosynthesis genes and trigger xylogenesis in Eucalyptus plants.

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Real time quantitative PCR (qPCR) is widely used in gene expression analysis for its accuracy and sensitivity. Reference genes serving as endogenous controls are necessary for gene normalization. In order to select an appropriate reference gene to normalize gene expression in Casuarina equisetifolia under salt stress, 10 potential reference genes were evaluated using real time qPCR in the leaves and roots of plants grown under different NaCl concentrations and treatment durations. GeNorm, NormFinder, and BestKeeper analyses reveal that elongation factor 1-alpha (EF1α) and ubiquitin-conjugating enzyme E2 (UBC) were the most appropriate reference genes for real time qPCR under salt stress. However, β-tubulin (βTUB) and actin 7, which were widely used as reference genes in other plant species, were not always stably expressed. The combination of EF1α, UBC, uncharacterized protein 2, DNAJ homolog subfamily A member 2, and glyceraldehyde-3-phosphate dehydrogenase should be ideal reference genes for normalizing gene expression data in all samples under salt stress. It indicates the need for reference gene selection for normalizing gene expression in C. equisetifolia. In addition, the suitability of reference genes selected was confirmed by validating the expression of WRKY29-like and expansin-like B1. The results enable analysis of salt response mechanism and gene expression in C. equisetifolia.

VQ genes play important roles in plant development, growth, and stress responses. However, little information regarding the functions of VQ genes is available for Eucalyptus grandis. In our study, genome-wide characterization and identification of VQ genes were performed in E. grandis. Results showed that 27 VQ genes, which divided into seven sub-families (I–VII), were found, and all but two VQ genes showed no intron by gene structure and conserved motif analysis. To further identify the function of EgrVQ proteins, gene expression analyses were also developed under hormone treatments (brassinosteroids, methyl jasmonate, salicylic acid, and abscisic acid) and abiotic conditions (salt stress, cold 4 °C, and heat 42 °C). The results of a quantitative real-time PCR analysis indicated that the EgrVQs were variously expressed under different hormone treatments and abiotic stressors. Our study provides a comprehensive overview of VQ genes in E. grandis, which will be beneficial in the molecular breeding of E. grandis to promote its resistance to abiotic stressors; the results also provide a basis from which to conduct further investigation into the functions of VQ genes in E. grandis.

Background High soil salinity seriously affects plant growth and development. Excessive salt ions mainly cause damage by inducing osmotic stress, ion toxicity, and oxidation stress. Casuarina equisetifolia is a highly salt-tolerant plant, commonly grown as wind belts in coastal areas with sandy soils. However, little is known about its physiology and the molecular mechanism of its response to salt stress. Results Eight-week-old C. equisetifolia seedlings grown from rooted cuttings were exposed to salt stress for varying durations (0, 1, 6, 24, and 168 h under 200 mM NaCl) and their ion contents, cellular structure, and transcriptomes were analyzed. Potassium concentration decreased slowly between 1 h and 24 h after initiation of salt treatment, while the content of potassium was significantly lower after 168 h of salt treatment. Root epidermal cells were shed and a more compact layer of cells formed as the treatment duration increased. Salt stress led to deformation of cells and damage to mitochondria in the epidermis and endodermis, whereas stele cells suffered less damage. Transcriptome analysis identified 10,378 differentially expressed genes (DEGs), with more genes showing differential expression after 24 h and 168 h of exposure than after shorter durations of exposure to salinity. Signal transduction and ion transport genes such as HKT and CHX were enriched among DEGs in the early stages (1 h or 6 h) of salt stress, while expression of genes involved in programmed cell death was significantly upregulated at 168 h, corresponding to changes in ion contents and cell structure of roots. Oxidative stress and detoxification genes were also expressed differentially and were enriched among DEGs at different stages. Conclusions These results not only elucidate the mechanism and the molecular pathway governing salt tolerance, but also serve as a basis for identifying gene function related to salt stress in C. equisetifolia.

Casuarina equisetifolia is widely planted in coastal areas of tropical and subtropical regions as windbreaks or to stabilize dunes against wind erosion due to its high salt tolerance and nitrogen-fixing ability. To investigate the mechanisms responsible for its salt tolerance, we examined growth, mineral composition, expression of genes for sodium (Na +) and potassium (K +) transport proteins, and antioxidant responses under NaCl treatments. Increasing NaCl concentrations inhibited lateral root elongation and decreased plant height, length of internodes, and numbers of branches and twigs. The Na + content significantly increased whereas the K + content significantly decreased in both shoots and roots with increasing external NaCl concentration, resulting in a significant increase in Na + /K + ratio. Most of the Na + /H + antiporter genes (NHXs) were obviously upregulated in roots after 24 and 168 h of salt stress, and NHX7 was especially induced after 168 h. Almost all salt overly sensitive (SOS) genes were induced after 168-h treatment. Additionally, activities of superoxide dismutase, glutathione peroxidase, and catalase were significantly changed in shoots and roots under salt stress. Hence, we conclude that salinity tolerance of C. equisetifolia mainly relied on sequestering excess Na + into vacuoles and on induced expression of NHX and SOS genes in roots and thus the maintenance of sufficient K + content in shoots.