Overexpression of PpSnRK1α in tomato enhanced salt tolerance by regulating ABA signaling pathway and reactive oxygen metabolism

Abstract

Background: SNF-related Kinase 1 (SnRK1) is a key component of the cell signaling network. SnRK1 is known to respond to a wide variety of stresses, but its exact role in salt stress response and tolerance is still largely unknown.

Results: In this study, we reported that overexpression of the gene encoding the α subunit of Prunus persica SnRK1 (PpSnRK1α) in tomato could improve salt stress tolerance. The increase in salt stress tolerance in PpSnRK1α-overexpressing plants was found to correlate with increased PpSnRK1α expression level and SnRK1 kinase activity. And PpSnRK1α overexpression lines exhibited a lower level of leaf damage as well as increased proline content and reduced malondialdehyde (MDA) compared with wild-type (WT) lines under salt stress. Furthermore, PpSnRK1α enhanced reactive oxygen species (ROS) metabolism by increasing the expression level of antioxidase genes and antioxidant enzyme activities. We further sequenced the transcriptomes of the WT and three PpSnRK1α overexpression lines using RNA-seq and identified about 1000 PpSnRK1α-regulated genes, including many antioxidant enzymes, and these genes were clearly enriched in the MAPK signaling pathway (plant), plant-pathogen interactions and plant hormone signaling transduction and can respond to stimuli, metabolic processes, and biological regulation. Furthermore, we identified the transcriptional levels of several salt stress-responsive genes, SlPP2C37, SlPYL4, SlPYL8, SlNAC022, SlNAC042, and SlSnRK2 family were altered significantly by PpSnRK1α, signifying that SnRK1α may be involved in the ABA signaling pathway to improve tomato salt tolerance. Overall, these findings provided new evidence for the underlying mechanism of SnRK1α conferment in plant salt tolerance phenotypes.

Conclusions: Our findings demonstrated that plant salt stress resistance can be affected by the regulation of the SnRK1α. Further molecular and genetic approaches will accelerate our knowledge of PpSnRK1α functions, and inform the genetic improvement of salt tolerance in tomato through genetic engineering and other related strategies.

Keywords: ABA signaling; PpSnRK1α; ROS metabolism; Salt tolerance.

Fig. 1

PpSnRK1α overexpression lines had higher SnRK1 activity and increased salt tolerance. a Relative expression level of SnRK1 (PCR was performed using homologous and specific fragments of PpSnRK1 (Prunus persica) and SlSnRK1 (Solanum lycopersicum) between WT plants and PpSnRK1α overexpressing plants). This picture was cropped for simplicity and intuitiveness, the original pictures were in Additional file 1b Determination of SnRK1 activity c REC of the WT and PpSnRK1α overexpression lines d Evans blue stain. Note: in b and c, the data are represented as means ± standard error (S.E.) of three biological replicates

Fig. 2

MDA, soluble sugar and proline contents in the WT and PpSnRK1α overexpression lines with and without the salt treatment. a MDA content b proline content c soluble sugar content. Three biological replicates were analyzed for each sample, and the data are represented as means ± S.E. of three technical repeats

Fig. 3

Antioxidant enzyme activities and the contents of O²⁻ in WT and PpSnRK1α overexpression lines. a Comparison of the O²⁻ content between the WT and PpSnRK1α overexpression lines, b NBT staining for superoxide in the leaves c Comparison of the CAT activity between the WT and PpSnRK1α overexpression lines d DAB staining for H₂O₂ in the leaves e, f Comparison of the SOD (e) and POD (f) activity between the WT and PpSnRK1α overexpression lines. Note: in a, c, e and f, each sample has three biological replicates. The data are shown as means ± S.E. of three technical repeats

Fig. 4

qRT-PCR analysis of the relative expression levels of SlSOD, SlPOD, SlCAT1 and SlSnRK2 genes (SlSnRK2.1- SlSnRK2.7) in the WT and PpSnRK1α overexpression lines

Fig. 5

Identification and functional annotation of the DEGs. a DEG identification. b KEGG classification analysis of the DEGs c GO classification analysis of the DEGs

Fig. 6

IGV (Integrative Genomics Viewer) visualization of genes by RNA-seq and results of RT-qPCR analysis of related genes a, c, e, g and i IGV visualization of SlPP2C37 (a), SlPYL4 (c), SlPYL8(e), SlNAC022 (g)and SlNAC042(i) b, d, f, h and j Results of RT-qPCR analysis of SlPP2C37 (b), SlPYL4 (d), SlPYL8(f), SlNAC022 (h)and SlNAC042(j). Note: in b, d, f, h and j, error bars indicate SEs (n = 3, 3 biological replicates). All values for WT and PpSnRK1α overexpression plants are statistically significantly different from each other (Student’s t-test; p-value < 0.05)

Fig. 7

The working model of PpSnRK1α regulating salt tolerance through the ABA signal transduction pathway and ROS mechanism. In the current working model, PpSnRK1α-overexpression improves the transcription levels of SOD, POD, and CAT1 as well as SOD, POD and CAT activity, reduces ROS production in plant cells. PpSnRK1α is involved in the ABA signaling pathway by altering the transcription levels of ABA receptors (SlPYL4, SlPYL8), PP2C (SlPP2C37) and SlSnRK2s, and thereby leads to an increase in tolerance to salt stress in tomato. Additionally, PpSnRK1α-overexpression increases the expression of SlNAC022, which has been proved to participate in ABA signaling transcription